[PATCH v2 0/3] Fixes for CVE-2021-3998 and CVE-2021-3999

[PATCH v2 0/3] Fixes for CVE-2021-3998 and CVE-2021-3999

[Siddhesh Poyarekar]

Add functions to make directory trees with paths longer than PATH_MAX
and use them to test fixes for CVE-2021-3998 and CVE-2021-3999.

Tested on x86_64 and i686.

Changes from v1:
- Try reducing directory name size to meet lower limits of some fuse
  filesystems
- Fixed review comments
- Credited Qualys in NEWS
- Use x* functions wherever possible
- Drop size check in linux getcwd implementation and rely only on the
  posix one to flag the error
- Fix formatting issues I had missed before.

Siddhesh Poyarekar (3):
  support: Add helpers to create paths longer than PATH_MAX
  realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX
    [BZ #28770]
  getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

 NEWS                                          |  10 +
 stdlib/Makefile                               |   1 +
 stdlib/canonicalize.c                         |  12 +-
 stdlib/tst-realpath-toolong.c                 |  49 ++++
 support/temp_file.c                           | 173 ++++++++++++-
 support/temp_file.h                           |   9 +
 sysdeps/posix/getcwd.c                        |   7 +
 sysdeps/unix/sysv/linux/Makefile              |   7 +-
 .../unix/sysv/linux/tst-getcwd-smallbuff.c    | 245 ++++++++++++++++++
 9 files changed, 501 insertions(+), 12 deletions(-)
 create mode 100644 stdlib/tst-realpath-toolong.c
 create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c

-- 
2.34.1

[PATCH v2 1/3] support: Add helpers to create paths longer than PATH_MAX

[Siddhesh Poyarekar]

Add new helpers support_create_and_chdir_toolong_temp_directory and
support_chdir_toolong_temp_directory to create and descend into
directory trees longer than PATH_MAX.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 support/temp_file.c | 173 +++++++++++++++++++++++++++++++++++++++++---
 support/temp_file.h |   9 +++
 2 files changed, 173 insertions(+), 9 deletions(-)

diff --git a/support/temp_file.c b/support/temp_file.c
index e7bb8aadb9..59060e573f 100644
--- a/support/temp_file.c
+++ b/support/temp_file.c
@@ -1,5 +1,6 @@
 /* Temporary file handling for tests.
    Copyright (C) 1998-2022 Free Software Foundation, Inc.
+   Copyright The GNU Tools Authors.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -20,15 +21,17 @@
    some 32-bit platforms. */
 #define _FILE_OFFSET_BITS 64
 
+#include <support/check.h>
 #include <support/temp_file.h>
 #include <support/temp_file-internal.h>
 #include <support/support.h>
 
+#include <errno.h>
 #include <paths.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <unistd.h>
+#include <xunistd.h>
 
 /* List of temporary files.  */
 static struct temp_name_list
@@ -36,14 +39,32 @@ static struct temp_name_list
   struct temp_name_list *next;
   char *name;
   pid_t owner;
+  bool toolong;
 } *temp_name_list;
 
 /* Location of the temporary files.  Set by the test skeleton via
    support_set_test_dir.  The string is not be freed.  */
 static const char *test_dir = _PATH_TMP;
 
-void
-add_temp_file (const char *name)
+/* Name of subdirectories in a too long temporary directory tree.  */
+static char *toolong_subdir;
+static bool toolong_subdir_initialized;
+
+/* Return the maximum size of path on the target.  */
+static inline size_t
+get_path_max (void)
+{
+#ifdef PATH_MAX
+  return PATH_MAX;
+#else
+  size_t path_max = pathconf ("/", _PC_PATH_MAX);
+  return (path_max < 0 ? 1024
+	  : path_max <= PTRDIFF_MAX ? path_max : PTRDIFF_MAX);
+#endif
+}
+
+static void
+add_temp_file_internal (const char *name, bool toolong)
 {
   struct temp_name_list *newp
     = (struct temp_name_list *) xcalloc (sizeof (*newp), 1);
@@ -53,12 +74,19 @@ add_temp_file (const char *name)
       newp->name = newname;
       newp->next = temp_name_list;
       newp->owner = getpid ();
+      newp->toolong = toolong;
       temp_name_list = newp;
     }
   else
     free (newp);
 }
 
+void
+add_temp_file (const char *name)
+{
+  add_temp_file_internal (name, false);
+}
+
 int
 create_temp_file_in_dir (const char *base, const char *dir, char **filename)
 {
@@ -90,8 +118,8 @@ create_temp_file (const char *base, char **filename)
   return create_temp_file_in_dir (base, test_dir, filename);
 }
 
-char *
-support_create_temp_directory (const char *base)
+static char *
+create_temp_directory_internal (const char *base, bool toolong)
 {
   char *path = xasprintf ("%s/%sXXXXXX", test_dir, base);
   if (mkdtemp (path) == NULL)
@@ -99,16 +127,132 @@ support_create_temp_directory (const char *base)
       printf ("error: mkdtemp (\"%s\"): %m", path);
       exit (1);
     }
-  add_temp_file (path);
+  add_temp_file_internal (path, toolong);
   return path;
 }
 
-/* Helper functions called by the test skeleton follow.  */
+char *
+support_create_temp_directory (const char *base)
+{
+  return create_temp_directory_internal (base, false);
+}
+
+static void
+ensure_toolong_subdir_initialized (void)
+{
+  if (!toolong_subdir_initialized)
+    FAIL_EXIT1 ("uninitialized toolong directory tree\n");
+}
+
+static void
+initialize_toolong_subdir (void)
+{
+  size_t sz = NAME_MAX;
+  char testname[NAME_MAX];
+  int ret;
+
+  if (toolong_subdir_initialized)
+    return;
+
+  memset (testname, 'X', sz - 1);
+
+  /* Explore the name limit on the file system.  This should typically be
+     NAME_MAX, but it could be less on some fuse filesystems.  */
+  do
+    {
+      struct stat statbuf;
+
+      testname[sz - 1] = '\0';
+      ret = stat (testname, &statbuf);
+    }
+  while (ret != 0 && errno == ENAMETOOLONG && (sz = sz / 2) > 0);
+
+  if (ret != 0 && errno == ENAMETOOLONG)
+    FAIL_EXIT1 ("stat (%s) failed with ENAMETOOLONG\n", testname);
+
+  toolong_subdir = xmalloc (sz);
+  strcpy (toolong_subdir, testname);
+  toolong_subdir_initialized = true;
+}
+
+char *
+support_create_and_chdir_toolong_temp_directory (const char *basename)
+{
+  size_t path_max = get_path_max ();
+
+  char *base = create_temp_directory_internal (basename, true);
+
+  xchdir (base);
+
+  initialize_toolong_subdir ();
+
+  size_t sz = strlen (toolong_subdir);
+
+  /* Create directories and descend into them so that the final path is larger
+     than PATH_MAX.  */
+  for (size_t i = 0; i <= path_max / sz; i++)
+    {
+      xmkdir (toolong_subdir, S_IRWXU);
+      xchdir (toolong_subdir);
+    }
+  return base;
+}
 
 void
-support_set_test_dir (const char *path)
+support_chdir_toolong_temp_directory (const char *base)
 {
-  test_dir = path;
+  size_t path_max = get_path_max ();
+  ensure_toolong_subdir_initialized ();
+
+  xchdir (base);
+
+  size_t sz = strlen (toolong_subdir);
+  for (size_t i = 0; i <= path_max / sz; i++)
+    xchdir (toolong_subdir);
+}
+
+/* Helper functions called by the test skeleton follow.  */
+
+static void
+remove_toolong_subdirs (const char *base)
+{
+  size_t path_max = get_path_max ();
+
+  ensure_toolong_subdir_initialized ();
+
+  if (chdir (base) != 0)
+    {
+      printf ("warning: toolong cleanup base failed: chdir (\"%s\"): %m\n",
+	      base);
+      return;
+    }
+
+  /* Descend.  */
+  int levels = 0;
+  size_t sz = strlen (toolong_subdir);
+  for (levels = 0; levels <= path_max / sz; levels++)
+    if (chdir (toolong_subdir) != 0)
+      {
+	printf ("warning: toolong cleanup failed: chdir (\"%s\"): %m\n",
+		toolong_subdir);
+	return;
+      }
+
+  /* Ascend and remove.  */
+  while (--levels >= 0)
+    {
+      if (chdir ("..") != 0)
+	{
+	  printf ("warning: toolong cleanup failed: chdir (\"..\"): %m\n");
+	  return;
+	}
+      if (remove (toolong_subdir) != 0)
+	{
+	  printf ("warning: could not remove subdirectory: %s: %m\n",
+		  toolong_subdir);
+	  return;
+	}
+    }
 }
 
 void
@@ -123,6 +267,9 @@ support_delete_temp_files (void)
 	 around, to prevent PID reuse.)  */
       if (temp_name_list->owner == pid)
 	{
+	  if (temp_name_list->toolong)
+	    remove_toolong_subdirs (temp_name_list->name);
+
 	  if (remove (temp_name_list->name) != 0)
 	    printf ("warning: could not remove temporary file: %s: %m\n",
 		    temp_name_list->name);
@@ -133,6 +280,8 @@ support_delete_temp_files (void)
       free (temp_name_list);
       temp_name_list = next;
     }
+
+  free (toolong_subdir);
 }
 
 void
@@ -147,3 +296,9 @@ support_print_temp_files (FILE *f)
       fprintf (f, ")\n");
     }
 }
+
+void
+support_set_test_dir (const char *path)
+{
+  test_dir = path;
+}
diff --git a/support/temp_file.h b/support/temp_file.h
index 50a443abe4..8459ddda72 100644
--- a/support/temp_file.h
+++ b/support/temp_file.h
@@ -44,6 +44,15 @@ int create_temp_file_in_dir (const char *base, const char *dir,
    returns.  The caller should free this string.  */
 char *support_create_temp_directory (const char *base);
 
+/* Create a temporary directory tree that is longer than PATH_MAX and schedule
+   it for deletion.  BASENAME is used as a prefix for the unique directory
+   name, which the function returns.  The caller should free this string.  */
+char *support_create_and_chdir_toolong_temp_directory (const char *basename);
+
+/* Change into the innermost directory of the directory tree BASE, which was
+   created using support_create_and_chdir_toolong_temp_directory.  */
+void support_chdir_toolong_temp_directory (const char *base);
+
 __END_DECLS
 
 #endif /* SUPPORT_TEMP_FILE_H */
-- 
2.34.1

Re: [PATCH v2 1/3] support: Add helpers to create paths longer than PATH_MAX

[Siddhesh Poyarekar]

On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
> Add new helpers support_create_and_chdir_toolong_temp_directory and
> support_chdir_toolong_temp_directory to create and descend into
> directory trees longer than PATH_MAX.
> 
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
> ---
>   support/temp_file.c | 173 +++++++++++++++++++++++++++++++++++++++++---
>   support/temp_file.h |   9 +++
>   2 files changed, 173 insertions(+), 9 deletions(-)
> 
> diff --git a/support/temp_file.c b/support/temp_file.c
> index e7bb8aadb9..59060e573f 100644
> --- a/support/temp_file.c
> +++ b/support/temp_file.c
> @@ -1,5 +1,6 @@
>   /* Temporary file handling for tests.
>      Copyright (C) 1998-2022 Free Software Foundation, Inc.
> +   Copyright The GNU Tools Authors.
>      This file is part of the GNU C Library.
>   
>      The GNU C Library is free software; you can redistribute it and/or
> @@ -20,15 +21,17 @@
>      some 32-bit platforms. */
>   #define _FILE_OFFSET_BITS 64
>   
> +#include <support/check.h>
>   #include <support/temp_file.h>
>   #include <support/temp_file-internal.h>
>   #include <support/support.h>
>   
> +#include <errno.h>
>   #include <paths.h>
>   #include <stdio.h>
>   #include <stdlib.h>
>   #include <string.h>
> -#include <unistd.h>
> +#include <xunistd.h>
>   
>   /* List of temporary files.  */
>   static struct temp_name_list
> @@ -36,14 +39,32 @@ static struct temp_name_list
>     struct temp_name_list *next;
>     char *name;
>     pid_t owner;
> +  bool toolong;
>   } *temp_name_list;
>   
>   /* Location of the temporary files.  Set by the test skeleton via
>      support_set_test_dir.  The string is not be freed.  */
>   static const char *test_dir = _PATH_TMP;
>   
> -void
> -add_temp_file (const char *name)
> +/* Name of subdirectories in a too long temporary directory tree.  */
> +static char *toolong_subdir;
> +static bool toolong_subdir_initialized;
> +
> +/* Return the maximum size of path on the target.  */
> +static inline size_t
> +get_path_max (void)
> +{
> +#ifdef PATH_MAX
> +  return PATH_MAX;
> +#else
> +  size_t path_max = pathconf ("/", _PC_PATH_MAX);
> +  return (path_max < 0 ? 1024
> +	  : path_max <= PTRDIFF_MAX ? path_max : PTRDIFF_MAX);
> +#endif
> +}
> +
> +static void
> +add_temp_file_internal (const char *name, bool toolong)
>   {
>     struct temp_name_list *newp
>       = (struct temp_name_list *) xcalloc (sizeof (*newp), 1);
> @@ -53,12 +74,19 @@ add_temp_file (const char *name)
>         newp->name = newname;
>         newp->next = temp_name_list;
>         newp->owner = getpid ();
> +      newp->toolong = toolong;
>         temp_name_list = newp;
>       }
>     else
>       free (newp);
>   }
>   
> +void
> +add_temp_file (const char *name)
> +{
> +  add_temp_file_internal (name, false);
> +}
> +
>   int
>   create_temp_file_in_dir (const char *base, const char *dir, char **filename)
>   {
> @@ -90,8 +118,8 @@ create_temp_file (const char *base, char **filename)
>     return create_temp_file_in_dir (base, test_dir, filename);
>   }
>   
> -char *
> -support_create_temp_directory (const char *base)
> +static char *
> +create_temp_directory_internal (const char *base, bool toolong)
>   {
>     char *path = xasprintf ("%s/%sXXXXXX", test_dir, base);
>     if (mkdtemp (path) == NULL)
> @@ -99,16 +127,132 @@ support_create_temp_directory (const char *base)
>         printf ("error: mkdtemp (\"%s\"): %m", path);
>         exit (1);
>       }
> -  add_temp_file (path);
> +  add_temp_file_internal (path, toolong);
>     return path;
>   }
>   
> -/* Helper functions called by the test skeleton follow.  */
> +char *
> +support_create_temp_directory (const char *base)
> +{
> +  return create_temp_directory_internal (base, false);
> +}
> +
> +static void
> +ensure_toolong_subdir_initialized (void)
> +{
> +  if (!toolong_subdir_initialized)
> +    FAIL_EXIT1 ("uninitialized toolong directory tree\n");
> +}
> +
> +static void
> +initialize_toolong_subdir (void)
> +{
> +  size_t sz = NAME_MAX;
> +  char testname[NAME_MAX];
> +  int ret;
> +
> +  if (toolong_subdir_initialized)
> +    return;
> +
> +  memset (testname, 'X', sz - 1);
> +
> +  /* Explore the name limit on the file system.  This should typically be
> +     NAME_MAX, but it could be less on some fuse filesystems.  */
> +  do
> +    {
> +      struct stat statbuf;
> +
> +      testname[sz - 1] = '\0';
> +      ret = stat (testname, &statbuf);
> +    }
> +  while (ret != 0 && errno == ENAMETOOLONG && (sz = sz / 2) > 0);
> +
> +  if (ret != 0 && errno == ENAMETOOLONG)
> +    FAIL_EXIT1 ("stat (%s) failed with ENAMETOOLONG\n", testname);
> +
> +  toolong_subdir = xmalloc (sz);
> +  strcpy (toolong_subdir, testname);
> +  toolong_subdir_initialized = true;
> +}
> +
> +char *
> +support_create_and_chdir_toolong_temp_directory (const char *basename)
> +{
> +  size_t path_max = get_path_max ();
> +
> +  char *base = create_temp_directory_internal (basename, true);
> +
> +  xchdir (base);
> +
> +  initialize_toolong_subdir ();
> +
> +  size_t sz = strlen (toolong_subdir);
> +
> +  /* Create directories and descend into them so that the final path is larger
> +     than PATH_MAX.  */
> +  for (size_t i = 0; i <= path_max / sz; i++)
> +    {
> +      xmkdir (toolong_subdir, S_IRWXU);

This still doesn't work on the trybot, which somehow fails with 
ENAMETOOLONG even though stat() on that length worked in 
initialize_toolong_subdir.  I'm going to need to reproduce the 
environment properly to figure out what's going on.

Siddhesh

> +      xchdir (toolong_subdir);
> +    }
> +  return base;
> +}
>   
>   void
> -support_set_test_dir (const char *path)
> +support_chdir_toolong_temp_directory (const char *base)
>   {
> -  test_dir = path;
> +  size_t path_max = get_path_max ();
> +  ensure_toolong_subdir_initialized ();
> +
> +  xchdir (base);
> +
> +  size_t sz = strlen (toolong_subdir);
> +  for (size_t i = 0; i <= path_max / sz; i++)
> +    xchdir (toolong_subdir);
> +}
> +
> +/* Helper functions called by the test skeleton follow.  */
> +
> +static void
> +remove_toolong_subdirs (const char *base)
> +{
> +  size_t path_max = get_path_max ();
> +
> +  ensure_toolong_subdir_initialized ();
> +
> +  if (chdir (base) != 0)
> +    {
> +      printf ("warning: toolong cleanup base failed: chdir (\"%s\"): %m\n",
> +	      base);
> +      return;
> +    }
> +
> +  /* Descend.  */
> +  int levels = 0;
> +  size_t sz = strlen (toolong_subdir);
> +  for (levels = 0; levels <= path_max / sz; levels++)
> +    if (chdir (toolong_subdir) != 0)
> +      {
> +	printf ("warning: toolong cleanup failed: chdir (\"%s\"): %m\n",
> +		toolong_subdir);
> +	return;
> +      }
> +
> +  /* Ascend and remove.  */
> +  while (--levels >= 0)
> +    {
> +      if (chdir ("..") != 0)
> +	{
> +	  printf ("warning: toolong cleanup failed: chdir (\"..\"): %m\n");
> +	  return;
> +	}
> +      if (remove (toolong_subdir) != 0)
> +	{
> +	  printf ("warning: could not remove subdirectory: %s: %m\n",
> +		  toolong_subdir);
> +	  return;
> +	}
> +    }
>   }
>   
>   void
> @@ -123,6 +267,9 @@ support_delete_temp_files (void)
>   	 around, to prevent PID reuse.)  */
>         if (temp_name_list->owner == pid)
>   	{
> +	  if (temp_name_list->toolong)
> +	    remove_toolong_subdirs (temp_name_list->name);
> +
>   	  if (remove (temp_name_list->name) != 0)
>   	    printf ("warning: could not remove temporary file: %s: %m\n",
>   		    temp_name_list->name);
> @@ -133,6 +280,8 @@ support_delete_temp_files (void)
>         free (temp_name_list);
>         temp_name_list = next;
>       }
> +
> +  free (toolong_subdir);
>   }
>   
>   void
> @@ -147,3 +296,9 @@ support_print_temp_files (FILE *f)
>         fprintf (f, ")\n");
>       }
>   }
> +
> +void
> +support_set_test_dir (const char *path)
> +{
> +  test_dir = path;
> +}
> diff --git a/support/temp_file.h b/support/temp_file.h
> index 50a443abe4..8459ddda72 100644
> --- a/support/temp_file.h
> +++ b/support/temp_file.h
> @@ -44,6 +44,15 @@ int create_temp_file_in_dir (const char *base, const char *dir,
>      returns.  The caller should free this string.  */
>   char *support_create_temp_directory (const char *base);
>   
> +/* Create a temporary directory tree that is longer than PATH_MAX and schedule
> +   it for deletion.  BASENAME is used as a prefix for the unique directory
> +   name, which the function returns.  The caller should free this string.  */
> +char *support_create_and_chdir_toolong_temp_directory (const char *basename);
> +
> +/* Change into the innermost directory of the directory tree BASE, which was
> +   created using support_create_and_chdir_toolong_temp_directory.  */
> +void support_chdir_toolong_temp_directory (const char *base);
> +
>   __END_DECLS
>   
>   #endif /* SUPPORT_TEMP_FILE_H */

Re: [PATCH v2 1/3] support: Add helpers to create paths longer than PATH_MAX

[Cristian Rodríguez]

On Wed, Jan 19, 2022 at 7:21 AM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>
> On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
> > Add new helpers support_create_and_chdir_toolong_temp_directory and
> > support_chdir_toolong_temp_directory to create and descend into
> > directory trees longer than PATH_MAX.

Note that recentish linux kernel versions do not allow d_name 's
larger than kernel 's PATH_MAX definition, in that case getdents
returns EIO, this behavior is since kernel 5.5.

Re: [PATCH v2 1/3] support: Add helpers to create paths longer than PATH_MAX

[Florian Weimer]

* Cristian Rodríguez:

> On Wed, Jan 19, 2022 at 7:21 AM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>>
>> On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
>> > Add new helpers support_create_and_chdir_toolong_temp_directory and
>> > support_chdir_toolong_temp_directory to create and descend into
>> > directory trees longer than PATH_MAX.
>
> Note that recentish linux kernel versions do not allow d_name 's
> larger than kernel 's PATH_MAX definition, in that case getdents
> returns EIO, this behavior is since kernel 5.5.

NAME_MAX or PATH_MAX?  d_name should be capped by NAME_MAX, but
historically it is not.

Thanks,
Florian

Re: [PATCH v2 1/3] support: Add helpers to create paths longer than PATH_MAX

[Cristian Rodríguez]

On Thu, Jan 20, 2022 at 11:56 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Cristian Rodríguez:
>
> > On Wed, Jan 19, 2022 at 7:21 AM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
> >>
> >> On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
> >> > Add new helpers support_create_and_chdir_toolong_temp_directory and
> >> > support_chdir_toolong_temp_directory to create and descend into
> >> > directory trees longer than PATH_MAX.
> >
> > Note that recentish linux kernel versions do not allow d_name 's
> > larger than kernel 's PATH_MAX definition, in that case getdents
> > returns EIO, this behavior is since kernel 5.5.
>
> NAME_MAX or PATH_MAX?  d_name should be capped by NAME_MAX, but
> historically it is not.

PATH_MAX.. I wrote that correctly,  see
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2c6b7bcd747201441923a0d3062577a8d1fbd8f8

Re: [PATCH v2 1/3] support: Add helpers to create paths longer than PATH_MAX

[Siddhesh Poyarekar]

On 20/01/2022 20:17, Cristian Rodríguez wrote:
> On Wed, Jan 19, 2022 at 7:21 AM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>>
>> On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
>>> Add new helpers support_create_and_chdir_toolong_temp_directory and
>>> support_chdir_toolong_temp_directory to create and descend into
>>> directory trees longer than PATH_MAX.
> 
> Note that recentish linux kernel versions do not allow d_name 's
> larger than kernel 's PATH_MAX definition, in that case getdents
> returns EIO, this behavior is since kernel 5.5.
> 

The d_name in these helpers is limited to _PC_NAME_MAX so AFAICT we 
shouldn't run into issues with that.

Thanks,
Siddhesh

[PATCH v2 2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX (CVE-2021-3998)

[Siddhesh Poyarekar]

realpath returns an allocated string when the result exceeds PATH_MAX,
which is unexpected when its second argument is not NULL.  This results
in the second argument (resolved) being uninitialized and also results
in a memory leak since the caller expects resolved to be the same as the
returned value.

Return NULL and set errno to ENAMETOOLONG if the result exceeds
PATH_MAX.  This fixes BZ #28770, which is CVE-2021-3998.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 NEWS                          |  4 +++
 stdlib/Makefile               |  1 +
 stdlib/canonicalize.c         | 12 +++++++--
 stdlib/tst-realpath-toolong.c | 49 +++++++++++++++++++++++++++++++++++
 4 files changed, 64 insertions(+), 2 deletions(-)
 create mode 100644 stdlib/tst-realpath-toolong.c

diff --git a/NEWS b/NEWS
index 6ed9fa9787..4c392a445e 100644
--- a/NEWS
+++ b/NEWS
@@ -166,6 +166,10 @@ Security related changes:
   CVE-2022-23218: Passing an overlong file name to the svcunix_create
   legacy function could result in a stack-based buffer overflow.
 
+  CVE-2021-3998: Passing a path longer than PATH_MAX to the realpath
+  function could result in a memory leak and potential access of
+  uninitialized memory.  Reported by Qualys.
+
 The following bugs are resolved with this release:
 
   [The release manager will add the list generated by
diff --git a/stdlib/Makefile b/stdlib/Makefile
index 1e81f98fac..8236741984 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -109,6 +109,7 @@ tests := \
   tst-random \
   tst-random2 \
   tst-realpath \
+  tst-realpath-toolong \
   tst-secure-getenv \
   tst-setcontext \
   tst-setcontext2 \
diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
index f36bdf4c76..732dc7ea46 100644
--- a/stdlib/canonicalize.c
+++ b/stdlib/canonicalize.c
@@ -400,8 +400,16 @@ realpath_stk (const char *name, char *resolved,
 
 error:
   *dest++ = '\0';
-  if (resolved != NULL && dest - rname <= get_path_max ())
-    rname = strcpy (resolved, rname);
+  if (resolved != NULL)
+    {
+      if (dest - rname <= get_path_max ())
+	rname = strcpy (resolved, rname);
+      else
+	{
+	  failed = true;
+	  __set_errno (ENAMETOOLONG);
+	}
+    }
 
 error_nomem:
   scratch_buffer_free (&extra_buffer);
diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c
new file mode 100644
index 0000000000..8bed772460
--- /dev/null
+++ b/stdlib/tst-realpath-toolong.c
@@ -0,0 +1,49 @@
+/* Verify that realpath returns NULL with ENAMETOOLONG if the result exceeds
+   NAME_MAX.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#define BASENAME "tst-realpath-toolong."
+
+int
+do_test (void)
+{
+  char *base = support_create_and_chdir_toolong_temp_directory (BASENAME);
+
+  char buf[PATH_MAX + 1];
+  const char *res = realpath (".", buf);
+
+  /* canonicalize.c states that if the real path is >= PATH_MAX, then
+     realpath returns NULL and sets ENAMETOOLONG.  */
+  TEST_VERIFY (res == NULL);
+  TEST_VERIFY (errno == ENAMETOOLONG);
+
+  free (base);
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.34.1

[PATCH v2 3/3] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Siddhesh Poyarekar]

No valid path returned by getcwd would fit into 1 byte, so reject the
size early and return NULL with errno set to ERANGE.  This change is
prompted by CVE-2021-3999, which describes a single byte buffer
underflow and overflow when all of the following conditions are met:

- The buffer size (i.e. the second argument of getcwd) is 1 byte
- The current working directory is too long
- '/' is also mounted on the current working directory

Sequence of events:

- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
  because the linux kernel checks for name length before it checks
  buffer size

- The code falls back to the generic getcwd in sysdeps/posix

- In the generic func, the buf[0] is set to '\0' on line 250

- this while loop on line 262 is bypassed:

    while (!(thisdev == rootdev && thisino == rootino))

  since the rootfs (/) is bind mounted onto the directory and the flow
  goes on to line 449, where it puts a '/' in the byte before the
  buffer.

- Finally on line 458, it moves 2 bytes (the underflowed byte and the
  '\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.

- buf is returned on line 469 and errno is not set.

This resolves BZ #28769.

Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 NEWS                                          |   6 +
 sysdeps/posix/getcwd.c                        |   7 +
 sysdeps/unix/sysv/linux/Makefile              |   7 +-
 .../unix/sysv/linux/tst-getcwd-smallbuff.c    | 245 ++++++++++++++++++
 4 files changed, 264 insertions(+), 1 deletion(-)
 create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c

diff --git a/NEWS b/NEWS
index 4c392a445e..07e9eac52d 100644
--- a/NEWS
+++ b/NEWS
@@ -170,6 +170,12 @@ Security related changes:
   function could result in a memory leak and potential access of
   uninitialized memory.  Reported by Qualys.
 
+  CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
+  function may result in an off-by-one buffer underflow and overflow
+  when the current working directory is longer than PATH_MAX and also
+  corresponds to the / directory through an unprivileged mount
+  namespace.  Reported by Qualys.
+
 The following bugs are resolved with this release:
 
   [The release manager will add the list generated by
diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
index e147a31a81..9d5787b6f4 100644
--- a/sysdeps/posix/getcwd.c
+++ b/sysdeps/posix/getcwd.c
@@ -187,6 +187,13 @@ __getcwd_generic (char *buf, size_t size)
   size_t allocated = size;
   size_t used;
 
+  /* A size of 1 byte is never useful.  */
+  if (allocated == 1)
+    {
+      __set_errno (ERANGE);
+      return NULL;
+    }
+
 #if HAVE_MINIMALLY_WORKING_GETCWD
   /* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
      this is much slower than the system getcwd (at least on
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 85fc8cbf75..7ca9350c99 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
 
 sysdep_headers += bits/fcntl-linux.h
 
-tests += tst-fallocate tst-fallocate64 tst-o_path-locks
+tests += \
+  tst-fallocate \
+  tst-fallocate64 \
+  tst-getcwd-smallbuff \
+  tst-o_path-locks \
+# tests
 endif
 
 ifeq ($(subdir),elf)
diff --git a/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
new file mode 100644
index 0000000000..791dfe4d02
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
@@ -0,0 +1,245 @@
+/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
+   buffer when the CWD is too long and is also a mount target of /.  See bug
+   #28769 or CVE-2021-3999 for more context.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <support/xsched.h>
+#include <support/xunistd.h>
+
+#ifndef PATH_MAX
+# define PATH_MAX 1024
+#endif
+
+static char *base;
+#define BASENAME "tst-getcwd-smallbuff"
+#define MOUNT_NAME "mpoint"
+static int sockfd[2];
+
+static void
+do_cleanup (void)
+{
+  support_chdir_toolong_temp_directory (base);
+  TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
+  free (base);
+}
+
+static void
+send_fd (const int sock, const int fd)
+{
+  struct msghdr msg;
+  union
+    {
+      struct cmsghdr hdr;
+      char buf[CMSG_SPACE (sizeof (int))];
+    } cmsgbuf;
+  struct cmsghdr *cmsg;
+  struct iovec vec;
+  char ch = 'A';
+  ssize_t n;
+
+  memset (&msg, 0, sizeof (msg));
+  memset (&cmsgbuf, 0, sizeof (cmsgbuf));
+  msg.msg_control = &cmsgbuf.buf;
+  msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+  cmsg = CMSG_FIRSTHDR (&msg);
+  cmsg->cmsg_len = CMSG_LEN (sizeof (int));
+  cmsg->cmsg_level = SOL_SOCKET;
+  cmsg->cmsg_type = SCM_RIGHTS;
+  *(int *) CMSG_DATA (cmsg) = fd;
+
+  vec.iov_base = &ch;
+  vec.iov_len = 1;
+  msg.msg_iov = &vec;
+  msg.msg_iovlen = 1;
+
+  while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+
+  TEST_VERIFY_EXIT (n == 1);
+}
+
+static int
+recv_fd (const int sock)
+{
+  struct msghdr msg;
+  union
+    {
+      struct cmsghdr hdr;
+      char buf[CMSG_SPACE(sizeof(int))];
+    } cmsgbuf;
+  struct cmsghdr *cmsg;
+  struct iovec vec;
+  ssize_t n;
+  char ch = '\0';
+  int fd = -1;
+
+  memset (&msg, 0, sizeof (msg));
+  vec.iov_base = &ch;
+  vec.iov_len = 1;
+  msg.msg_iov = &vec;
+  msg.msg_iovlen = 1;
+
+  memset (&cmsgbuf, 0, sizeof (cmsgbuf));
+  msg.msg_control = &cmsgbuf.buf;
+  msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+  while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+  if (n != 1 || ch != 'A')
+    return -1;
+
+  cmsg = CMSG_FIRSTHDR (&msg);
+  if (cmsg == NULL)
+    return -1;
+  if (cmsg->cmsg_type != SCM_RIGHTS)
+    return -1;
+  fd = *(const int *) CMSG_DATA (cmsg);
+  if (fd < 0)
+    return -1;
+  return fd;
+}
+
+static int
+child_func (void * const arg)
+{
+  xclose (sockfd[0]);
+  const int sock = sockfd[1];
+  char ch;
+
+  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+  TEST_VERIFY_EXIT (ch == '1');
+
+  if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
+    FAIL_EXIT1 ("mount failed: %m\n");
+  const int fd = xopen ("mpoint",
+			O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
+
+  send_fd (sock, fd);
+  xclose (fd);
+
+  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+  TEST_VERIFY_EXIT (ch == 'a');
+
+  xclose (sock);
+  return 0;
+}
+
+static void
+update_map (char * const mapping, const char * const map_file)
+{
+  const size_t map_len = strlen (mapping);
+
+  const int fd = xopen (map_file, O_WRONLY, 0);
+  xwrite (fd, mapping, map_len);
+  xclose (fd);
+}
+
+static void
+proc_setgroups_write (const long child_pid, const char * const str)
+{
+  const size_t str_len = strlen(str);
+
+  char setgroups_path[64];
+  snprintf (setgroups_path, sizeof (setgroups_path),
+	    "/proc/%ld/setgroups", child_pid);
+
+  const int fd = open (setgroups_path, O_WRONLY);
+
+  if (fd < 0)
+    {
+      TEST_VERIFY_EXIT (errno == ENOENT);
+      FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
+    }
+
+  xwrite (fd, str, str_len);
+  xclose(fd);
+}
+
+static char child_stack[1024 * 1024];
+
+int
+do_test (void)
+{
+  base = support_create_and_chdir_toolong_temp_directory (BASENAME);
+
+  xmkdir (MOUNT_NAME, S_IRWXU);
+  atexit (do_cleanup);
+
+  TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
+  pid_t child_pid = xclone (child_func, NULL, child_stack,
+			    sizeof (child_stack),
+			    CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
+
+  xclose (sockfd[1]);
+  const int sock = sockfd[0];
+
+  char map_path[64], map_buf[64];
+  snprintf (map_path, sizeof (map_path), "/proc/%ld/uid_map",
+	    (long) child_pid);
+  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
+  update_map (map_buf, map_path);
+
+  proc_setgroups_write ((long) child_pid, "deny");
+  snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
+	    (long) child_pid);
+  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
+  update_map (map_buf, map_path);
+
+  TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
+  const int fd = recv_fd (sock);
+  TEST_VERIFY_EXIT (fd >= 0);
+  TEST_VERIFY_EXIT (fchdir (fd) == 0);
+
+  static char buf[2 * 10 + 1];
+  memset (buf, 'A', sizeof(buf));
+
+  /* Finally, call getcwd and check if it resulted in a buffer underflow.  */
+  char * cwd = getcwd (buf + sizeof(buf) / 2, 1);
+  TEST_VERIFY (cwd == NULL);
+  TEST_VERIFY (errno == ERANGE);
+
+  for (int i = 0; i < sizeof (buf); i++)
+    if (buf[i] != 'A')
+      {
+	printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
+	support_record_failure ();
+      }
+
+  TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
+  xclose (sock);
+  TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
+
+  return 0;
+}
+
+#define CLEANUP_HANDLER do_cleanup
+#include <support/test-driver.c>
-- 
2.34.1

[PATCH v3 0/3] Fixes for CVE-2021-3998 and CVE-2021-3999

[Siddhesh Poyarekar]

Add functions to make directory trees with paths longer than PATH_MAX
and use them to test fixes for CVE-2021-3998 and CVE-2021-3999.

Tested on x86_64 and i686.

Changes from v2:
- Adjusted test infrastructure to bail out if the filesystem does not support
  creating directory trees greater than PATH_MAX.

Changes from v1:
- Try reducing directory name size to meet lower limits of some fuse
  filesystems
- Fixed review comments
- Credited Qualys in NEWS
- Use x* functions wherever possible
- Drop size check in linux getcwd implementation and rely only on the
  posix one to flag the error
- Fix formatting issues I had missed before.

Siddhesh Poyarekar (3):
  support: Add helpers to create paths longer than PATH_MAX
  realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX
    [BZ #28770]
  getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

 NEWS                                          |  10 +
 stdlib/Makefile                               |   1 +
 stdlib/canonicalize.c                         |  12 +-
 stdlib/tst-realpath-toolong.c                 |  49 ++++
 support/temp_file.c                           | 159 +++++++++++-
 support/temp_file.h                           |   9 +
 sysdeps/posix/getcwd.c                        |   7 +
 sysdeps/unix/sysv/linux/Makefile              |   7 +-
 .../unix/sysv/linux/tst-getcwd-smallbuff.c    | 245 ++++++++++++++++++
 9 files changed, 487 insertions(+), 12 deletions(-)
 create mode 100644 stdlib/tst-realpath-toolong.c
 create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c

-- 
2.34.1

[PATCH v3 1/3] support: Add helpers to create paths longer than PATH_MAX

[Siddhesh Poyarekar]

Add new helpers support_create_and_chdir_toolong_temp_directory and
support_chdir_toolong_temp_directory to create and descend into
directory trees longer than PATH_MAX.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 support/temp_file.c | 159 +++++++++++++++++++++++++++++++++++++++++---
 support/temp_file.h |   9 +++
 2 files changed, 159 insertions(+), 9 deletions(-)

diff --git a/support/temp_file.c b/support/temp_file.c
index e7bb8aadb9..e41128c2d4 100644
--- a/support/temp_file.c
+++ b/support/temp_file.c
@@ -1,5 +1,6 @@
 /* Temporary file handling for tests.
    Copyright (C) 1998-2022 Free Software Foundation, Inc.
+   Copyright The GNU Tools Authors.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -20,15 +21,17 @@
    some 32-bit platforms. */
 #define _FILE_OFFSET_BITS 64
 
+#include <support/check.h>
 #include <support/temp_file.h>
 #include <support/temp_file-internal.h>
 #include <support/support.h>
 
+#include <errno.h>
 #include <paths.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <unistd.h>
+#include <xunistd.h>
 
 /* List of temporary files.  */
 static struct temp_name_list
@@ -36,14 +39,20 @@ static struct temp_name_list
   struct temp_name_list *next;
   char *name;
   pid_t owner;
+  bool toolong;
 } *temp_name_list;
 
 /* Location of the temporary files.  Set by the test skeleton via
    support_set_test_dir.  The string is not be freed.  */
 static const char *test_dir = _PATH_TMP;
 
-void
-add_temp_file (const char *name)
+/* Name of subdirectories in a too long temporary directory tree.  */
+static char toolong_subdir[NAME_MAX + 1];
+static bool toolong_initialized;
+static size_t toolong_path_max;
+
+static void
+add_temp_file_internal (const char *name, bool toolong)
 {
   struct temp_name_list *newp
     = (struct temp_name_list *) xcalloc (sizeof (*newp), 1);
@@ -53,12 +62,19 @@ add_temp_file (const char *name)
       newp->name = newname;
       newp->next = temp_name_list;
       newp->owner = getpid ();
+      newp->toolong = toolong;
       temp_name_list = newp;
     }
   else
     free (newp);
 }
 
+void
+add_temp_file (const char *name)
+{
+  add_temp_file_internal (name, false);
+}
+
 int
 create_temp_file_in_dir (const char *base, const char *dir, char **filename)
 {
@@ -90,8 +106,8 @@ create_temp_file (const char *base, char **filename)
   return create_temp_file_in_dir (base, test_dir, filename);
 }
 
-char *
-support_create_temp_directory (const char *base)
+static char *
+create_temp_directory_internal (const char *base, bool toolong)
 {
   char *path = xasprintf ("%s/%sXXXXXX", test_dir, base);
   if (mkdtemp (path) == NULL)
@@ -99,16 +115,132 @@ support_create_temp_directory (const char *base)
       printf ("error: mkdtemp (\"%s\"): %m", path);
       exit (1);
     }
-  add_temp_file (path);
+  add_temp_file_internal (path, toolong);
   return path;
 }
 
-/* Helper functions called by the test skeleton follow.  */
+char *
+support_create_temp_directory (const char *base)
+{
+  return create_temp_directory_internal (base, false);
+}
+
+static void
+ensure_toolong_initialized (void)
+{
+  if (!toolong_initialized)
+    FAIL_EXIT1 ("uninitialized toolong directory tree\n");
+}
+
+static void
+initialize_toolong (const char *base)
+{
+  long name_max = pathconf (base, _PC_NAME_MAX);
+  name_max = (name_max < 0 ? 64
+	      : (name_max < sizeof (toolong_subdir) ? name_max
+		 : sizeof (toolong_subdir) - 1));
+
+  long path_max = pathconf (base, _PC_PATH_MAX);
+  path_max = (path_max < 0 ? 1024
+	      : path_max <= PTRDIFF_MAX ? path_max : PTRDIFF_MAX);
+
+  /* Sanity check to ensure that the test does not create temporary directories
+     in different filesystems because this API doesn't support it.  */
+  if (toolong_initialized)
+    {
+      if (name_max != strlen (toolong_subdir))
+	FAIL_UNSUPPORTED ("name_max: Temporary directories in different"
+			  " filesystems not supported yet\n");
+      if (path_max != toolong_path_max)
+	FAIL_UNSUPPORTED ("path_max: Temporary directories in different"
+			  " filesystems not supported yet\n");
+      return;
+    }
+
+  toolong_path_max = path_max;
+
+  size_t len = name_max;
+  memset (toolong_subdir, 'X', len);
+  toolong_initialized = true;
+}
+
+char *
+support_create_and_chdir_toolong_temp_directory (const char *basename)
+{
+  char *base = create_temp_directory_internal (basename, true);
+  xchdir (base);
+
+  initialize_toolong (base);
+
+  size_t sz = strlen (toolong_subdir);
+
+  /* Create directories and descend into them so that the final path is larger
+     than PATH_MAX.  */
+  for (size_t i = 0; i <= toolong_path_max / sz; i++)
+    {
+      int ret = mkdir (toolong_subdir, S_IRWXU);
+      if (ret != 0 && errno == ENAMETOOLONG)
+	FAIL_UNSUPPORTED ("Filesystem does not support creating too long "
+			  "directory trees\n");
+      else if (ret != 0)
+	FAIL_EXIT1 ("Failed to create directory tree: %m\n");
+      xchdir (toolong_subdir);
+    }
+  return base;
+}
 
 void
-support_set_test_dir (const char *path)
+support_chdir_toolong_temp_directory (const char *base)
 {
-  test_dir = path;
+  ensure_toolong_initialized ();
+
+  xchdir (base);
+
+  size_t sz = strlen (toolong_subdir);
+  for (size_t i = 0; i <= toolong_path_max / sz; i++)
+    xchdir (toolong_subdir);
+}
+
+/* Helper functions called by the test skeleton follow.  */
+
+static void
+remove_toolong_subdirs (const char *base)
+{
+  ensure_toolong_initialized ();
+
+  if (chdir (base) != 0)
+    {
+      printf ("warning: toolong cleanup base failed: chdir (\"%s\"): %m\n",
+	      base);
+      return;
+    }
+
+  /* Descend.  */
+  int levels = 0;
+  size_t sz = strlen (toolong_subdir);
+  for (levels = 0; levels <= toolong_path_max / sz; levels++)
+    if (chdir (toolong_subdir) != 0)
+      {
+	printf ("warning: toolong cleanup failed: chdir (\"%s\"): %m\n",
+		toolong_subdir);
+	break;
+      }
+
+  /* Ascend and remove.  */
+  while (--levels >= 0)
+    {
+      if (chdir ("..") != 0)
+	{
+	  printf ("warning: toolong cleanup failed: chdir (\"..\"): %m\n");
+	  return;
+	}
+      if (remove (toolong_subdir) != 0)
+	{
+	  printf ("warning: could not remove subdirectory: %s: %m\n",
+		  toolong_subdir);
+	  return;
+	}
+    }
 }
 
 void
@@ -123,6 +255,9 @@ support_delete_temp_files (void)
 	 around, to prevent PID reuse.)  */
       if (temp_name_list->owner == pid)
 	{
+	  if (temp_name_list->toolong)
+	    remove_toolong_subdirs (temp_name_list->name);
+
 	  if (remove (temp_name_list->name) != 0)
 	    printf ("warning: could not remove temporary file: %s: %m\n",
 		    temp_name_list->name);
@@ -147,3 +282,9 @@ support_print_temp_files (FILE *f)
       fprintf (f, ")\n");
     }
 }
+
+void
+support_set_test_dir (const char *path)
+{
+  test_dir = path;
+}
diff --git a/support/temp_file.h b/support/temp_file.h
index 50a443abe4..8459ddda72 100644
--- a/support/temp_file.h
+++ b/support/temp_file.h
@@ -44,6 +44,15 @@ int create_temp_file_in_dir (const char *base, const char *dir,
    returns.  The caller should free this string.  */
 char *support_create_temp_directory (const char *base);
 
+/* Create a temporary directory tree that is longer than PATH_MAX and schedule
+   it for deletion.  BASENAME is used as a prefix for the unique directory
+   name, which the function returns.  The caller should free this string.  */
+char *support_create_and_chdir_toolong_temp_directory (const char *basename);
+
+/* Change into the innermost directory of the directory tree BASE, which was
+   created using support_create_and_chdir_toolong_temp_directory.  */
+void support_chdir_toolong_temp_directory (const char *base);
+
 __END_DECLS
 
 #endif /* SUPPORT_TEMP_FILE_H */
-- 
2.34.1

Re: [PATCH v3 1/3] support: Add helpers to create paths longer than PATH_MAX

[Adhemerval Zanella]

On 20/01/2022 06:32, Siddhesh Poyarekar wrote:
> Add new helpers support_create_and_chdir_toolong_temp_directory and
> support_chdir_toolong_temp_directory to create and descend into
> directory trees longer than PATH_MAX.
> 
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  support/temp_file.c | 159 +++++++++++++++++++++++++++++++++++++++++---
>  support/temp_file.h |   9 +++
>  2 files changed, 159 insertions(+), 9 deletions(-)
> 
> diff --git a/support/temp_file.c b/support/temp_file.c
> index e7bb8aadb9..e41128c2d4 100644
> --- a/support/temp_file.c
> +++ b/support/temp_file.c
> @@ -1,5 +1,6 @@
>  /* Temporary file handling for tests.
>     Copyright (C) 1998-2022 Free Software Foundation, Inc.
> +   Copyright The GNU Tools Authors.
>     This file is part of the GNU C Library.
>  
>     The GNU C Library is free software; you can redistribute it and/or
> @@ -20,15 +21,17 @@
>     some 32-bit platforms. */
>  #define _FILE_OFFSET_BITS 64
>  
> +#include <support/check.h>
>  #include <support/temp_file.h>
>  #include <support/temp_file-internal.h>
>  #include <support/support.h>
>  
> +#include <errno.h>
>  #include <paths.h>
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <string.h>
> -#include <unistd.h>
> +#include <xunistd.h>
>  
>  /* List of temporary files.  */
>  static struct temp_name_list
> @@ -36,14 +39,20 @@ static struct temp_name_list
>    struct temp_name_list *next;
>    char *name;
>    pid_t owner;
> +  bool toolong;
>  } *temp_name_list;
>  
>  /* Location of the temporary files.  Set by the test skeleton via
>     support_set_test_dir.  The string is not be freed.  */
>  static const char *test_dir = _PATH_TMP;
>  
> -void
> -add_temp_file (const char *name)
> +/* Name of subdirectories in a too long temporary directory tree.  */
> +static char toolong_subdir[NAME_MAX + 1];
> +static bool toolong_initialized;
> +static size_t toolong_path_max;
> +

I think it is suffice for current tests, although it would need to change
if any tests requires more than one large path.

> +static void
> +add_temp_file_internal (const char *name, bool toolong)
>  {
>    struct temp_name_list *newp
>      = (struct temp_name_list *) xcalloc (sizeof (*newp), 1);
> @@ -53,12 +62,19 @@ add_temp_file (const char *name)
>        newp->name = newname;
>        newp->next = temp_name_list;
>        newp->owner = getpid ();
> +      newp->toolong = toolong;
>        temp_name_list = newp;
>      }
>    else
>      free (newp);
>  }
>  
> +void
> +add_temp_file (const char *name)
> +{
> +  add_temp_file_internal (name, false);
> +}
> +
>  int
>  create_temp_file_in_dir (const char *base, const char *dir, char **filename)
>  {
> @@ -90,8 +106,8 @@ create_temp_file (const char *base, char **filename)
>    return create_temp_file_in_dir (base, test_dir, filename);
>  }
>  
> -char *
> -support_create_temp_directory (const char *base)
> +static char *
> +create_temp_directory_internal (const char *base, bool toolong)
>  {
>    char *path = xasprintf ("%s/%sXXXXXX", test_dir, base);
>    if (mkdtemp (path) == NULL)
> @@ -99,16 +115,132 @@ support_create_temp_directory (const char *base)
>        printf ("error: mkdtemp (\"%s\"): %m", path);
>        exit (1);
>      }
> -  add_temp_file (path);
> +  add_temp_file_internal (path, toolong);
>    return path;
>  }
>  
> -/* Helper functions called by the test skeleton follow.  */
> +char *
> +support_create_temp_directory (const char *base)
> +{
> +  return create_temp_directory_internal (base, false);
> +}
> +
> +static void
> +ensure_toolong_initialized (void)
> +{
> +  if (!toolong_initialized)
> +    FAIL_EXIT1 ("uninitialized toolong directory tree\n");
> +}
> +
> +static void
> +initialize_toolong (const char *base)
> +{
> +  long name_max = pathconf (base, _PC_NAME_MAX);
> +  name_max = (name_max < 0 ? 64
> +	      : (name_max < sizeof (toolong_subdir) ? name_max
> +		 : sizeof (toolong_subdir) - 1));
> +
> +  long path_max = pathconf (base, _PC_PATH_MAX);
> +  path_max = (path_max < 0 ? 1024
> +	      : path_max <= PTRDIFF_MAX ? path_max : PTRDIFF_MAX);
> +
> +  /* Sanity check to ensure that the test does not create temporary directories
> +     in different filesystems because this API doesn't support it.  */
> +  if (toolong_initialized)
> +    {
> +      if (name_max != strlen (toolong_subdir))
> +	FAIL_UNSUPPORTED ("name_max: Temporary directories in different"
> +			  " filesystems not supported yet\n");
> +      if (path_max != toolong_path_max)
> +	FAIL_UNSUPPORTED ("path_max: Temporary directories in different"
> +			  " filesystems not supported yet\n");
> +      return;
> +    }
> +
> +  toolong_path_max = path_max;
> +
> +  size_t len = name_max;
> +  memset (toolong_subdir, 'X', len);
> +  toolong_initialized = true;
> +}
> +

Ok.

> +char *
> +support_create_and_chdir_toolong_temp_directory (const char *basename)
> +{> +  char *base = create_temp_directory_internal (basename, true);
> +  xchdir (base);
> +
> +  initialize_toolong (base);
> +
> +  size_t sz = strlen (toolong_subdir);
> +
> +  /* Create directories and descend into them so that the final path is larger
> +     than PATH_MAX.  */
> +  for (size_t i = 0; i <= toolong_path_max / sz; i++)
> +    {
> +      int ret = mkdir (toolong_subdir, S_IRWXU);
> +      if (ret != 0 && errno == ENAMETOOLONG)
> +	FAIL_UNSUPPORTED ("Filesystem does not support creating too long "
> +			  "directory trees\n");
> +      else if (ret != 0)
> +	FAIL_EXIT1 ("Failed to create directory tree: %m\n");
> +      xchdir (toolong_subdir);
> +    }
> +  return base;
> +}
>  
>  void
> -support_set_test_dir (const char *path)
> +support_chdir_toolong_temp_directory (const char *base)
>  {
> -  test_dir = path;
> +  ensure_toolong_initialized ();
> +
> +  xchdir (base);
> +
> +  size_t sz = strlen (toolong_subdir);
> +  for (size_t i = 0; i <= toolong_path_max / sz; i++)
> +    xchdir (toolong_subdir);
> +}
> +
> +/* Helper functions called by the test skeleton follow.  */
> +
> +static void
> +remove_toolong_subdirs (const char *base)
> +{
> +  ensure_toolong_initialized ();
> +
> +  if (chdir (base) != 0)
> +    {
> +      printf ("warning: toolong cleanup base failed: chdir (\"%s\"): %m\n",
> +	      base);
> +      return;
> +    }

I think there is no much we co in such case.

> +
> +  /* Descend.  */
> +  int levels = 0;
> +  size_t sz = strlen (toolong_subdir);
> +  for (levels = 0; levels <= toolong_path_max / sz; levels++)
> +    if (chdir (toolong_subdir) != 0)
> +      {
> +	printf ("warning: toolong cleanup failed: chdir (\"%s\"): %m\n",
> +		toolong_subdir);
> +	break;
> +      }
> +
> +  /* Ascend and remove.  */
> +  while (--levels >= 0)
> +    {
> +      if (chdir ("..") != 0)
> +	{
> +	  printf ("warning: toolong cleanup failed: chdir (\"..\"): %m\n");
> +	  return;
> +	}
> +      if (remove (toolong_subdir) != 0)
> +	{
> +	  printf ("warning: could not remove subdirectory: %s: %m\n",
> +		  toolong_subdir);
> +	  return;
> +	}
> +    }
>  }
>  
>  void
> @@ -123,6 +255,9 @@ support_delete_temp_files (void)
>  	 around, to prevent PID reuse.)  */
>        if (temp_name_list->owner == pid)
>  	{
> +	  if (temp_name_list->toolong)
> +	    remove_toolong_subdirs (temp_name_list->name);
> +
>  	  if (remove (temp_name_list->name) != 0)
>  	    printf ("warning: could not remove temporary file: %s: %m\n",
>  		    temp_name_list->name);
> @@ -147,3 +282,9 @@ support_print_temp_files (FILE *f)
>        fprintf (f, ")\n");
>      }
>  }
> +
> +void
> +support_set_test_dir (const char *path)
> +{
> +  test_dir = path;
> +}
> diff --git a/support/temp_file.h b/support/temp_file.h
> index 50a443abe4..8459ddda72 100644
> --- a/support/temp_file.h
> +++ b/support/temp_file.h
> @@ -44,6 +44,15 @@ int create_temp_file_in_dir (const char *base, const char *dir,
>     returns.  The caller should free this string.  */
>  char *support_create_temp_directory (const char *base);
>  
> +/* Create a temporary directory tree that is longer than PATH_MAX and schedule
> +   it for deletion.  BASENAME is used as a prefix for the unique directory
> +   name, which the function returns.  The caller should free this string.  */
> +char *support_create_and_chdir_toolong_temp_directory (const char *basename);
> +
> +/* Change into the innermost directory of the directory tree BASE, which was
> +   created using support_create_and_chdir_toolong_temp_directory.  */
> +void support_chdir_toolong_temp_directory (const char *base);
> +
>  __END_DECLS
>  
>  #endif /* SUPPORT_TEMP_FILE_H */

[PATCH v3 2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]

[Siddhesh Poyarekar]

realpath returns an allocated string when the result exceeds PATH_MAX,
which is unexpected when its second argument is not NULL.  This results
in the second argument (resolved) being uninitialized and also results
in a memory leak since the caller expects resolved to be the same as the
returned value.

Return NULL and set errno to ENAMETOOLONG if the result exceeds
PATH_MAX.  This fixes [BZ #28770], which is CVE-2021-3998.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 NEWS                          |  4 +++
 stdlib/Makefile               |  1 +
 stdlib/canonicalize.c         | 12 +++++++--
 stdlib/tst-realpath-toolong.c | 49 +++++++++++++++++++++++++++++++++++
 4 files changed, 64 insertions(+), 2 deletions(-)
 create mode 100644 stdlib/tst-realpath-toolong.c

diff --git a/NEWS b/NEWS
index 6ed9fa9787..4c392a445e 100644
--- a/NEWS
+++ b/NEWS
@@ -166,6 +166,10 @@ Security related changes:
   CVE-2022-23218: Passing an overlong file name to the svcunix_create
   legacy function could result in a stack-based buffer overflow.
 
+  CVE-2021-3998: Passing a path longer than PATH_MAX to the realpath
+  function could result in a memory leak and potential access of
+  uninitialized memory.  Reported by Qualys.
+
 The following bugs are resolved with this release:
 
   [The release manager will add the list generated by
diff --git a/stdlib/Makefile b/stdlib/Makefile
index 1e81f98fac..8236741984 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -109,6 +109,7 @@ tests := \
   tst-random \
   tst-random2 \
   tst-realpath \
+  tst-realpath-toolong \
   tst-secure-getenv \
   tst-setcontext \
   tst-setcontext2 \
diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
index f36bdf4c76..732dc7ea46 100644
--- a/stdlib/canonicalize.c
+++ b/stdlib/canonicalize.c
@@ -400,8 +400,16 @@ realpath_stk (const char *name, char *resolved,
 
 error:
   *dest++ = '\0';
-  if (resolved != NULL && dest - rname <= get_path_max ())
-    rname = strcpy (resolved, rname);
+  if (resolved != NULL)
+    {
+      if (dest - rname <= get_path_max ())
+	rname = strcpy (resolved, rname);
+      else
+	{
+	  failed = true;
+	  __set_errno (ENAMETOOLONG);
+	}
+    }
 
 error_nomem:
   scratch_buffer_free (&extra_buffer);
diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c
new file mode 100644
index 0000000000..8bed772460
--- /dev/null
+++ b/stdlib/tst-realpath-toolong.c
@@ -0,0 +1,49 @@
+/* Verify that realpath returns NULL with ENAMETOOLONG if the result exceeds
+   NAME_MAX.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#define BASENAME "tst-realpath-toolong."
+
+int
+do_test (void)
+{
+  char *base = support_create_and_chdir_toolong_temp_directory (BASENAME);
+
+  char buf[PATH_MAX + 1];
+  const char *res = realpath (".", buf);
+
+  /* canonicalize.c states that if the real path is >= PATH_MAX, then
+     realpath returns NULL and sets ENAMETOOLONG.  */
+  TEST_VERIFY (res == NULL);
+  TEST_VERIFY (errno == ENAMETOOLONG);
+
+  free (base);
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.34.1

Re: [PATCH v3 2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]

[Joseph Myers]

On Thu, 20 Jan 2022, Siddhesh Poyarekar via Libc-alpha wrote:

> diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c

> +  char buf[PATH_MAX + 1];

This has broken the testsuite build for Hurd.

tst-realpath-toolong.c: In function 'do_test':
tst-realpath-toolong.c:37:12: error: 'PATH_MAX' undeclared (first use in this function)

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [PATCH v3 2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]

[Siddhesh Poyarekar]

On 22/01/2022 04:52, Joseph Myers wrote:
> On Thu, 20 Jan 2022, Siddhesh Poyarekar via Libc-alpha wrote:
> 
>> diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c
> 
>> +  char buf[PATH_MAX + 1];
> 
> This has broken the testsuite build for Hurd.
> 
> tst-realpath-toolong.c: In function 'do_test':
> tst-realpath-toolong.c:37:12: error: 'PATH_MAX' undeclared (first use in this function)
> 

Sorry I missed that, I'll post a fix.  I was getting a different build 
error on hurd which prevented me from seeing this.  I'm rebuilding my 
build-many-glibcs to see if that fixes it.

Thanks,
Siddhesh

[PATCH] tst-realpath-toolong: Fix hurd build

[Siddhesh Poyarekar]

We don't really need a bigger buffer for realpath since it should fail
and return NULL.  In the bug too, the buffer itself is not accessed; it
is in fact left untouched.  Drop the PATH_MAX use and pass a single char
address.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 stdlib/tst-realpath-toolong.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c
index 8bed772460..ed84787a32 100644
--- a/stdlib/tst-realpath-toolong.c
+++ b/stdlib/tst-realpath-toolong.c
@@ -34,8 +34,8 @@ do_test (void)
 {
   char *base = support_create_and_chdir_toolong_temp_directory (BASENAME);
 
-  char buf[PATH_MAX + 1];
-  const char *res = realpath (".", buf);
+  char buf;
+  const char *res = realpath (".", &buf);
 
   /* canonicalize.c states that if the real path is >= PATH_MAX, then
      realpath returns NULL and sets ENAMETOOLONG.  */
-- 
2.34.1

Re: [PATCH] tst-realpath-toolong: Fix hurd build

[Samuel Thibault]

Siddhesh Poyarekar via Libc-alpha, le sam. 22 janv. 2022 20:15:23 +0530, a ecrit:
> We don't really need a bigger buffer for realpath since it should fail
> and return NULL.  In the bug too, the buffer itself is not accessed; it
> is in fact left untouched.  Drop the PATH_MAX use and pass a single char
> address.

? realpath assumes that the passed buffer is PATH_MAX-long. When
PATH_MAX is not defined, calling it with a buffer is essentially
undefined. Better just pass NULL.

> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
> ---
>  stdlib/tst-realpath-toolong.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c
> index 8bed772460..ed84787a32 100644
> --- a/stdlib/tst-realpath-toolong.c
> +++ b/stdlib/tst-realpath-toolong.c
> @@ -34,8 +34,8 @@ do_test (void)
>  {
>    char *base = support_create_and_chdir_toolong_temp_directory (BASENAME);
>  
> -  char buf[PATH_MAX + 1];
> -  const char *res = realpath (".", buf);
> +  char buf;
> +  const char *res = realpath (".", &buf);
>  
>    /* canonicalize.c states that if the real path is >= PATH_MAX, then
>       realpath returns NULL and sets ENAMETOOLONG.  */
> -- 
> 2.34.1
> 

Re: [PATCH] tst-realpath-toolong: Fix hurd build

[Siddhesh Poyarekar]

On 23/01/2022 06:06, Samuel Thibault wrote:
> Siddhesh Poyarekar via Libc-alpha, le sam. 22 janv. 2022 20:15:23 +0530, a ecrit:
>> We don't really need a bigger buffer for realpath since it should fail
>> and return NULL.  In the bug too, the buffer itself is not accessed; it
>> is in fact left untouched.  Drop the PATH_MAX use and pass a single char
>> address.
> 
> ? realpath assumes that the passed buffer is PATH_MAX-long. When
> PATH_MAX is not defined, calling it with a buffer is essentially
> undefined. Better just pass NULL.

Passing NULL doesn't reproduce the problem because realpath just 
allocates enough to accommodate the return, even when it exceeds 
PATH_MAX.  It only applies when a non-NULL buffer is supplied.

Would you prefer it if I defined PATH_MAX on hurd then, something like:

#ifndef PATH_MAX
# define PATH_MAX 1024
#endif

or do you prefer a more accurate path_max value using pathconf()?

The former will be a simpler fix, the latter will be best served by a 
get_path_max support function, which will be more elaborate but 
accurate.  I'm happy to do either.

Thanks,
Siddhesh

Re: [PATCH] tst-realpath-toolong: Fix hurd build

[Samuel Thibault]

Siddhesh Poyarekar, le dim. 23 janv. 2022 20:49:48 +0530, a ecrit:
> On 23/01/2022 06:06, Samuel Thibault wrote:
> > Siddhesh Poyarekar via Libc-alpha, le sam. 22 janv. 2022 20:15:23 +0530, a ecrit:
> > > We don't really need a bigger buffer for realpath since it should fail
> > > and return NULL.  In the bug too, the buffer itself is not accessed; it
> > > is in fact left untouched.  Drop the PATH_MAX use and pass a single char
> > > address.
> > 
> > ? realpath assumes that the passed buffer is PATH_MAX-long. When
> > PATH_MAX is not defined, calling it with a buffer is essentially
> > undefined. Better just pass NULL.
> 
> Passing NULL doesn't reproduce the problem because realpath just allocates
> enough to accommodate the return, even when it exceeds PATH_MAX.

Ah, ok, sorry I didn't check the whole story.

> Would you prefer it if I defined PATH_MAX on hurd then, something like:
> 
> #ifndef PATH_MAX
> # define PATH_MAX 1024
> #endif
> 
> or do you prefer a more accurate path_max value using pathconf()?

Better use the accurate from pathconf() ; that being said it will return
-1 on the ext2fs filesystem, so we'll have to resort to a hardcoded
limit in that case anyway. I'm fine with just setting PATH_MAX by hand
here.

Samuel

[committed v2] tst-realpath-toolong: Fix hurd build

[Siddhesh Poyarekar]

Thanks, I've committed this after confirming that build-many-glibcs
works for i686-gnu.

-->8--

Define PATH_MAX to a constant if it isn't already defined, like in hurd.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 stdlib/tst-realpath-toolong.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c
index 8bed772460..4388890294 100644
--- a/stdlib/tst-realpath-toolong.c
+++ b/stdlib/tst-realpath-toolong.c
@@ -29,6 +29,10 @@
 
 #define BASENAME "tst-realpath-toolong."
 
+#ifndef PATH_MAX
+# define PATH_MAX 1024
+#endif
+
 int
 do_test (void)
 {
-- 
2.34.1

Re: [PATCH v3 2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]

[Andreas Schwab]

On Jan 20 2022, Siddhesh Poyarekar via Libc-alpha wrote:

> diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
> index f36bdf4c76..732dc7ea46 100644
> --- a/stdlib/canonicalize.c
> +++ b/stdlib/canonicalize.c
> @@ -400,8 +400,16 @@ realpath_stk (const char *name, char *resolved,
>  
>  error:
>    *dest++ = '\0';
> -  if (resolved != NULL && dest - rname <= get_path_max ())
> -    rname = strcpy (resolved, rname);
> +  if (resolved != NULL)
> +    {
> +      if (dest - rname <= get_path_max ())
> +	rname = strcpy (resolved, rname);
> +      else
> +	{
> +	  failed = true;
> +	  __set_errno (ENAMETOOLONG);
> +	}
> +    }

Shouldn't that preserve any preexisting error?  I think the result
should only be copied if !failed.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: [PATCH v3 2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]

[Siddhesh Poyarekar]

On 24/01/2022 19:15, Andreas Schwab wrote:
> On Jan 20 2022, Siddhesh Poyarekar via Libc-alpha wrote:
> 
>> diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
>> index f36bdf4c76..732dc7ea46 100644
>> --- a/stdlib/canonicalize.c
>> +++ b/stdlib/canonicalize.c
>> @@ -400,8 +400,16 @@ realpath_stk (const char *name, char *resolved,
>>   
>>   error:
>>     *dest++ = '\0';
>> -  if (resolved != NULL && dest - rname <= get_path_max ())
>> -    rname = strcpy (resolved, rname);
>> +  if (resolved != NULL)
>> +    {
>> +      if (dest - rname <= get_path_max ())
>> +	rname = strcpy (resolved, rname);
>> +      else
>> +	{
>> +	  failed = true;
>> +	  __set_errno (ENAMETOOLONG);
>> +	}
>> +    }
> 
> Shouldn't that preserve any preexisting error?  

like this?

diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
index 732dc7ea46..6caed9e70e 100644
--- a/stdlib/canonicalize.c
+++ b/stdlib/canonicalize.c
@@ -404,7 +404,7 @@ error:
      {
        if (dest - rname <= get_path_max ())
  	rname = strcpy (resolved, rname);
-      else
+      else if (!failed)
  	{
  	  failed = true;
  	  __set_errno (ENAMETOOLONG);

> I think the result
> should only be copied if !failed.
> 

Looks like tests in test-canon.c depend on buf contents having being 
copied in despite failure.

Siddhesh

Re: [PATCH v3 2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]

[Andreas Schwab]

On Jan 24 2022, Siddhesh Poyarekar wrote:

> Looks like tests in test-canon.c depend on buf contents having being
> copied in despite failure.

That is not supported by POSIX.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: [PATCH v3 2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]

[Siddhesh Poyarekar]

On 24/01/2022 20:18, Andreas Schwab wrote:
> On Jan 24 2022, Siddhesh Poyarekar wrote:
> 
>> Looks like tests in test-canon.c depend on buf contents having being
>> copied in despite failure.
> 
> That is not supported by POSIX.
> 

OK, I'll file a separate bug and fix for it then.  Is the fix I posted 
sufficient for your other concern, i.e. not overriding preexisting error?

Thanks,
Siddhesh

Re: [PATCH v3 2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]

[Andreas Schwab]

On Jan 24 2022, Siddhesh Poyarekar wrote:

> Is the fix I posted sufficient for your other concern, i.e. not
> overriding preexisting error?

Yes.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

[committed] realpath: Avoid overwriting preexisting error (CVE-2021-3998)

[Siddhesh Poyarekar]

Set errno and failure for paths that are too long only if no other error
occurred earlier.

Related: BZ #28770

Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 stdlib/canonicalize.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
index 732dc7ea46..6caed9e70e 100644
--- a/stdlib/canonicalize.c
+++ b/stdlib/canonicalize.c
@@ -404,7 +404,7 @@ error:
     {
       if (dest - rname <= get_path_max ())
 	rname = strcpy (resolved, rname);
-      else
+      else if (!failed)
 	{
 	  failed = true;
 	  __set_errno (ENAMETOOLONG);
-- 
2.34.1

[PATCH v3 3/3] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Siddhesh Poyarekar]

No valid path returned by getcwd would fit into 1 byte, so reject the
size early and return NULL with errno set to ERANGE.  This change is
prompted by CVE-2021-3999, which describes a single byte buffer
underflow and overflow when all of the following conditions are met:

- The buffer size (i.e. the second argument of getcwd) is 1 byte
- The current working directory is too long
- '/' is also mounted on the current working directory

Sequence of events:

- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
  because the linux kernel checks for name length before it checks
  buffer size

- The code falls back to the generic getcwd in sysdeps/posix

- In the generic func, the buf[0] is set to '\0' on line 250

- this while loop on line 262 is bypassed:

    while (!(thisdev == rootdev && thisino == rootino))

  since the rootfs (/) is bind mounted onto the directory and the flow
  goes on to line 449, where it puts a '/' in the byte before the
  buffer.

- Finally on line 458, it moves 2 bytes (the underflowed byte and the
  '\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.

- buf is returned on line 469 and errno is not set.

This resolves BZ #28769.

Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 NEWS                                          |   6 +
 sysdeps/posix/getcwd.c                        |   7 +
 sysdeps/unix/sysv/linux/Makefile              |   7 +-
 .../unix/sysv/linux/tst-getcwd-smallbuff.c    | 245 ++++++++++++++++++
 4 files changed, 264 insertions(+), 1 deletion(-)
 create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c

diff --git a/NEWS b/NEWS
index 4c392a445e..07e9eac52d 100644
--- a/NEWS
+++ b/NEWS
@@ -170,6 +170,12 @@ Security related changes:
   function could result in a memory leak and potential access of
   uninitialized memory.  Reported by Qualys.
 
+  CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
+  function may result in an off-by-one buffer underflow and overflow
+  when the current working directory is longer than PATH_MAX and also
+  corresponds to the / directory through an unprivileged mount
+  namespace.  Reported by Qualys.
+
 The following bugs are resolved with this release:
 
   [The release manager will add the list generated by
diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
index e147a31a81..9d5787b6f4 100644
--- a/sysdeps/posix/getcwd.c
+++ b/sysdeps/posix/getcwd.c
@@ -187,6 +187,13 @@ __getcwd_generic (char *buf, size_t size)
   size_t allocated = size;
   size_t used;
 
+  /* A size of 1 byte is never useful.  */
+  if (allocated == 1)
+    {
+      __set_errno (ERANGE);
+      return NULL;
+    }
+
 #if HAVE_MINIMALLY_WORKING_GETCWD
   /* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
      this is much slower than the system getcwd (at least on
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 85fc8cbf75..7ca9350c99 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
 
 sysdep_headers += bits/fcntl-linux.h
 
-tests += tst-fallocate tst-fallocate64 tst-o_path-locks
+tests += \
+  tst-fallocate \
+  tst-fallocate64 \
+  tst-getcwd-smallbuff \
+  tst-o_path-locks \
+# tests
 endif
 
 ifeq ($(subdir),elf)
diff --git a/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
new file mode 100644
index 0000000000..791dfe4d02
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
@@ -0,0 +1,245 @@
+/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
+   buffer when the CWD is too long and is also a mount target of /.  See bug
+   #28769 or CVE-2021-3999 for more context.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <support/xsched.h>
+#include <support/xunistd.h>
+
+#ifndef PATH_MAX
+# define PATH_MAX 1024
+#endif
+
+static char *base;
+#define BASENAME "tst-getcwd-smallbuff"
+#define MOUNT_NAME "mpoint"
+static int sockfd[2];
+
+static void
+do_cleanup (void)
+{
+  support_chdir_toolong_temp_directory (base);
+  TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
+  free (base);
+}
+
+static void
+send_fd (const int sock, const int fd)
+{
+  struct msghdr msg;
+  union
+    {
+      struct cmsghdr hdr;
+      char buf[CMSG_SPACE (sizeof (int))];
+    } cmsgbuf;
+  struct cmsghdr *cmsg;
+  struct iovec vec;
+  char ch = 'A';
+  ssize_t n;
+
+  memset (&msg, 0, sizeof (msg));
+  memset (&cmsgbuf, 0, sizeof (cmsgbuf));
+  msg.msg_control = &cmsgbuf.buf;
+  msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+  cmsg = CMSG_FIRSTHDR (&msg);
+  cmsg->cmsg_len = CMSG_LEN (sizeof (int));
+  cmsg->cmsg_level = SOL_SOCKET;
+  cmsg->cmsg_type = SCM_RIGHTS;
+  *(int *) CMSG_DATA (cmsg) = fd;
+
+  vec.iov_base = &ch;
+  vec.iov_len = 1;
+  msg.msg_iov = &vec;
+  msg.msg_iovlen = 1;
+
+  while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+
+  TEST_VERIFY_EXIT (n == 1);
+}
+
+static int
+recv_fd (const int sock)
+{
+  struct msghdr msg;
+  union
+    {
+      struct cmsghdr hdr;
+      char buf[CMSG_SPACE(sizeof(int))];
+    } cmsgbuf;
+  struct cmsghdr *cmsg;
+  struct iovec vec;
+  ssize_t n;
+  char ch = '\0';
+  int fd = -1;
+
+  memset (&msg, 0, sizeof (msg));
+  vec.iov_base = &ch;
+  vec.iov_len = 1;
+  msg.msg_iov = &vec;
+  msg.msg_iovlen = 1;
+
+  memset (&cmsgbuf, 0, sizeof (cmsgbuf));
+  msg.msg_control = &cmsgbuf.buf;
+  msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+  while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+  if (n != 1 || ch != 'A')
+    return -1;
+
+  cmsg = CMSG_FIRSTHDR (&msg);
+  if (cmsg == NULL)
+    return -1;
+  if (cmsg->cmsg_type != SCM_RIGHTS)
+    return -1;
+  fd = *(const int *) CMSG_DATA (cmsg);
+  if (fd < 0)
+    return -1;
+  return fd;
+}
+
+static int
+child_func (void * const arg)
+{
+  xclose (sockfd[0]);
+  const int sock = sockfd[1];
+  char ch;
+
+  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+  TEST_VERIFY_EXIT (ch == '1');
+
+  if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
+    FAIL_EXIT1 ("mount failed: %m\n");
+  const int fd = xopen ("mpoint",
+			O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
+
+  send_fd (sock, fd);
+  xclose (fd);
+
+  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+  TEST_VERIFY_EXIT (ch == 'a');
+
+  xclose (sock);
+  return 0;
+}
+
+static void
+update_map (char * const mapping, const char * const map_file)
+{
+  const size_t map_len = strlen (mapping);
+
+  const int fd = xopen (map_file, O_WRONLY, 0);
+  xwrite (fd, mapping, map_len);
+  xclose (fd);
+}
+
+static void
+proc_setgroups_write (const long child_pid, const char * const str)
+{
+  const size_t str_len = strlen(str);
+
+  char setgroups_path[64];
+  snprintf (setgroups_path, sizeof (setgroups_path),
+	    "/proc/%ld/setgroups", child_pid);
+
+  const int fd = open (setgroups_path, O_WRONLY);
+
+  if (fd < 0)
+    {
+      TEST_VERIFY_EXIT (errno == ENOENT);
+      FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
+    }
+
+  xwrite (fd, str, str_len);
+  xclose(fd);
+}
+
+static char child_stack[1024 * 1024];
+
+int
+do_test (void)
+{
+  base = support_create_and_chdir_toolong_temp_directory (BASENAME);
+
+  xmkdir (MOUNT_NAME, S_IRWXU);
+  atexit (do_cleanup);
+
+  TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
+  pid_t child_pid = xclone (child_func, NULL, child_stack,
+			    sizeof (child_stack),
+			    CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
+
+  xclose (sockfd[1]);
+  const int sock = sockfd[0];
+
+  char map_path[64], map_buf[64];
+  snprintf (map_path, sizeof (map_path), "/proc/%ld/uid_map",
+	    (long) child_pid);
+  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
+  update_map (map_buf, map_path);
+
+  proc_setgroups_write ((long) child_pid, "deny");
+  snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
+	    (long) child_pid);
+  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
+  update_map (map_buf, map_path);
+
+  TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
+  const int fd = recv_fd (sock);
+  TEST_VERIFY_EXIT (fd >= 0);
+  TEST_VERIFY_EXIT (fchdir (fd) == 0);
+
+  static char buf[2 * 10 + 1];
+  memset (buf, 'A', sizeof(buf));
+
+  /* Finally, call getcwd and check if it resulted in a buffer underflow.  */
+  char * cwd = getcwd (buf + sizeof(buf) / 2, 1);
+  TEST_VERIFY (cwd == NULL);
+  TEST_VERIFY (errno == ERANGE);
+
+  for (int i = 0; i < sizeof (buf); i++)
+    if (buf[i] != 'A')
+      {
+	printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
+	support_record_failure ();
+      }
+
+  TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
+  xclose (sock);
+  TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
+
+  return 0;
+}
+
+#define CLEANUP_HANDLER do_cleanup
+#include <support/test-driver.c>
-- 
2.34.1

Re: [PATCH v3 3/3] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Andreas Schwab]

Ok.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: [PATCH v3 3/3] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Adhemerval Zanella]

On 20/01/2022 06:32, Siddhesh Poyarekar wrote:
> No valid path returned by getcwd would fit into 1 byte, so reject the
> size early and return NULL with errno set to ERANGE.  This change is
> prompted by CVE-2021-3999, which describes a single byte buffer
> underflow and overflow when all of the following conditions are met:
> 
> - The buffer size (i.e. the second argument of getcwd) is 1 byte
> - The current working directory is too long
> - '/' is also mounted on the current working directory
> 
> Sequence of events:
> 
> - In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
>   because the linux kernel checks for name length before it checks
>   buffer size
> 
> - The code falls back to the generic getcwd in sysdeps/posix
> 
> - In the generic func, the buf[0] is set to '\0' on line 250
> 
> - this while loop on line 262 is bypassed:
> 
>     while (!(thisdev == rootdev && thisino == rootino))
> 
>   since the rootfs (/) is bind mounted onto the directory and the flow
>   goes on to line 449, where it puts a '/' in the byte before the
>   buffer.
> 
> - Finally on line 458, it moves 2 bytes (the underflowed byte and the
>   '\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
> 
> - buf is returned on line 469 and errno is not set.
> 
> This resolves BZ #28769.
> 
> Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

Look good with just two fixed below for CMSG_DATA and a couple of comments.
Ok with the fixes, the comments would be good but it is a blocker.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  NEWS                                          |   6 +
>  sysdeps/posix/getcwd.c                        |   7 +
>  sysdeps/unix/sysv/linux/Makefile              |   7 +-
>  .../unix/sysv/linux/tst-getcwd-smallbuff.c    | 245 ++++++++++++++++++
>  4 files changed, 264 insertions(+), 1 deletion(-)
>  create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
> 
> diff --git a/NEWS b/NEWS
> index 4c392a445e..07e9eac52d 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -170,6 +170,12 @@ Security related changes:
>    function could result in a memory leak and potential access of
>    uninitialized memory.  Reported by Qualys.
>  
> +  CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
> +  function may result in an off-by-one buffer underflow and overflow
> +  when the current working directory is longer than PATH_MAX and also
> +  corresponds to the / directory through an unprivileged mount
> +  namespace.  Reported by Qualys.
> +
>  The following bugs are resolved with this release:
>  
>    [The release manager will add the list generated by
> diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
> index e147a31a81..9d5787b6f4 100644
> --- a/sysdeps/posix/getcwd.c
> +++ b/sysdeps/posix/getcwd.c
> @@ -187,6 +187,13 @@ __getcwd_generic (char *buf, size_t size)
>    size_t allocated = size;
>    size_t used;
>  
> +  /* A size of 1 byte is never useful.  */
> +  if (allocated == 1)
> +    {
> +      __set_errno (ERANGE);
> +      return NULL;
> +    }
> +
>  #if HAVE_MINIMALLY_WORKING_GETCWD
>    /* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
>       this is much slower than the system getcwd (at least on
> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> index 85fc8cbf75..7ca9350c99 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
>  
>  sysdep_headers += bits/fcntl-linux.h
>  
> -tests += tst-fallocate tst-fallocate64 tst-o_path-locks
> +tests += \
> +  tst-fallocate \
> +  tst-fallocate64 \
> +  tst-getcwd-smallbuff \
> +  tst-o_path-locks \
> +# tests
>  endif
>  
>  ifeq ($(subdir),elf)
> diff --git a/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
> new file mode 100644
> index 0000000000..791dfe4d02
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
> @@ -0,0 +1,245 @@
> +/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
> +   buffer when the CWD is too long and is also a mount target of /.  See bug
> +   #28769 or CVE-2021-3999 for more context.
> +   Copyright The GNU Toolchain Authors.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <limits.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/mount.h>
> +#include <sys/stat.h>
> +#include <sys/types.h>
> +#include <sys/wait.h>
> +
> +#include <sys/socket.h>
> +#include <sys/un.h>
> +#include <support/check.h>
> +#include <support/temp_file.h>
> +#include <support/xsched.h>
> +#include <support/xunistd.h>
> +
> +#ifndef PATH_MAX
> +# define PATH_MAX 1024
> +#endif

No need since it is a Linux only test and PATH_MAX is always defined.

> +
> +static char *base;
> +#define BASENAME "tst-getcwd-smallbuff"
> +#define MOUNT_NAME "mpoint"
> +static int sockfd[2];
> +
> +static void
> +do_cleanup (void)
> +{
> +  support_chdir_toolong_temp_directory (base);
> +  TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
> +  free (base);
> +}
> +
> +static void
> +send_fd (const int sock, const int fd)
> +{
> +  struct msghdr msg;
> +  union
> +    {
> +      struct cmsghdr hdr;
> +      char buf[CMSG_SPACE (sizeof (int))];
> +    } cmsgbuf;

Maybe zero-initialize both first to avoid the memset below?

> +  struct cmsghdr *cmsg;
> +  struct iovec vec;
> +  char ch = 'A';
> +  ssize_t n;
> +
> +  memset (&msg, 0, sizeof (msg));
> +  memset (&cmsgbuf, 0, sizeof (cmsgbuf));
> +  msg.msg_control = &cmsgbuf.buf;
> +  msg.msg_controllen = sizeof (cmsgbuf.buf);
> +
> +  cmsg = CMSG_FIRSTHDR (&msg);
> +  cmsg->cmsg_len = CMSG_LEN (sizeof (int));
> +  cmsg->cmsg_level = SOL_SOCKET;
> +  cmsg->cmsg_type = SCM_RIGHTS;
> +  *(int *) CMSG_DATA (cmsg) = fd;

I think CMSG_DATA does not guarantee the alignment, so I think it would be 
safe to use memcpy here:

  memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));

> +
> +  vec.iov_base = &ch;
> +  vec.iov_len = 1;
> +  msg.msg_iov = &vec;
> +  msg.msg_iovlen = 1;
> +
> +  while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
> +
> +  TEST_VERIFY_EXIT (n == 1);
> +}
> +

Ok.

> +static int
> +recv_fd (const int sock)
> +{
> +  struct msghdr msg;

Maybe also zero-initialize here.

> +  union
> +    {
> +      struct cmsghdr hdr;
> +      char buf[CMSG_SPACE(sizeof(int))];
> +    } cmsgbuf;
> +  struct cmsghdr *cmsg;
> +  struct iovec vec;
> +  ssize_t n;
> +  char ch = '\0';
> +  int fd = -1;
> +
> +  memset (&msg, 0, sizeof (msg));
> +  vec.iov_base = &ch;
> +  vec.iov_len = 1;
> +  msg.msg_iov = &vec;
> +  msg.msg_iovlen = 1;
> +
> +  memset (&cmsgbuf, 0, sizeof (cmsgbuf));
> +  msg.msg_control = &cmsgbuf.buf;
> +  msg.msg_controllen = sizeof (cmsgbuf.buf);
> +
> +  while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
> +  if (n != 1 || ch != 'A')
> +    return -1;
> +
> +  cmsg = CMSG_FIRSTHDR (&msg);
> +  if (cmsg == NULL)
> +    return -1;
> +  if (cmsg->cmsg_type != SCM_RIGHTS)
> +    return -1;
> +  fd = *(const int *) CMSG_DATA (cmsg);

Same as before, I think you will need to copy to a temporary using memcpy.

> +  if (fd < 0)
> +    return -1;
> +  return fd;
> +}
> +
> +static int
> +child_func (void * const arg)
> +{
> +  xclose (sockfd[0]);
> +  const int sock = sockfd[1];
> +  char ch;
> +
> +  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
> +  TEST_VERIFY_EXIT (ch == '1');
> +
> +  if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
> +    FAIL_EXIT1 ("mount failed: %m\n");
> +  const int fd = xopen ("mpoint",
> +			O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
> +
> +  send_fd (sock, fd);
> +  xclose (fd);
> +
> +  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
> +  TEST_VERIFY_EXIT (ch == 'a');
> +
> +  xclose (sock);
> +  return 0;
> +}
> +
> +static void
> +update_map (char * const mapping, const char * const map_file)
> +{
> +  const size_t map_len = strlen (mapping);
> +
> +  const int fd = xopen (map_file, O_WRONLY, 0);
> +  xwrite (fd, mapping, map_len);
> +  xclose (fd);
> +}
> +
> +static void
> +proc_setgroups_write (const long child_pid, const char * const str)
> +{
> +  const size_t str_len = strlen(str);
> +
> +  char setgroups_path[64];


Maybe define the size as:

  /* The path is the form /proc/%ld/setgroups.  */
  char map_path[sizeof("/proc/setgroups") + INT_STRLEN_BOUND (long int)];


> +  snprintf (setgroups_path, sizeof (setgroups_path),
> +	    "/proc/%ld/setgroups", child_pid);
> +
> +  const int fd = open (setgroups_path, O_WRONLY);
> +
> +  if (fd < 0)
> +    {
> +      TEST_VERIFY_EXIT (errno == ENOENT);
> +      FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
> +    }
> +
> +  xwrite (fd, str, str_len);
> +  xclose(fd);
> +}
> +
> +static char child_stack[1024 * 1024];
> +
> +int
> +do_test (void)
> +{
> +  base = support_create_and_chdir_toolong_temp_directory (BASENAME);
> +
> +  xmkdir (MOUNT_NAME, S_IRWXU);
> +  atexit (do_cleanup);
> +
> +  TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
> +  pid_t child_pid = xclone (child_func, NULL, child_stack,
> +			    sizeof (child_stack),
> +			    CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
> +
> +  xclose (sockfd[1]);
> +  const int sock = sockfd[0];
> +
> +  char map_path[64], map_buf[64];

Same comment as for setgroups_path.

> +  snprintf (map_path, sizeof (map_path),  ,
> +	    (long) child_pid);
> +  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
> +  update_map (map_buf, map_path);
> +
> +  proc_setgroups_write ((long) child_pid, "deny");
> +  snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
> +	    (long) child_pid);
> +  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
> +  update_map (map_buf, map_path);
> +
> +  TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
> +  const int fd = recv_fd (sock);
> +  TEST_VERIFY_EXIT (fd >= 0);
> +  TEST_VERIFY_EXIT (fchdir (fd) == 0);
> +
> +  static char buf[2 * 10 + 1];
> +  memset (buf, 'A', sizeof(buf));


Space before (.

> +
> +  /* Finally, call getcwd and check if it resulted in a buffer underflow.  */
> +  char * cwd = getcwd (buf + sizeof(buf) / 2, 1);
> +  TEST_VERIFY (cwd == NULL);
> +  TEST_VERIFY (errno == ERANGE);
> +
> +  for (int i = 0; i < sizeof (buf); i++)
> +    if (buf[i] != 'A')
> +      {
> +	printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
> +	support_record_failure ();
> +      }
> +
> +  TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
> +  xclose (sock);
> +  TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
> +
> +  return 0;
> +}
> +
> +#define CLEANUP_HANDLER do_cleanup
> +#include <support/test-driver.c>

Re: [PATCH v3 3/3] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Siddhesh Poyarekar]

On 21/01/2022 22:11, Adhemerval Zanella wrote:
> 
> 
> On 20/01/2022 06:32, Siddhesh Poyarekar wrote:
>> No valid path returned by getcwd would fit into 1 byte, so reject the
>> size early and return NULL with errno set to ERANGE.  This change is
>> prompted by CVE-2021-3999, which describes a single byte buffer
>> underflow and overflow when all of the following conditions are met:
>>
>> - The buffer size (i.e. the second argument of getcwd) is 1 byte
>> - The current working directory is too long
>> - '/' is also mounted on the current working directory
>>
>> Sequence of events:
>>
>> - In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
>>    because the linux kernel checks for name length before it checks
>>    buffer size
>>
>> - The code falls back to the generic getcwd in sysdeps/posix
>>
>> - In the generic func, the buf[0] is set to '\0' on line 250
>>
>> - this while loop on line 262 is bypassed:
>>
>>      while (!(thisdev == rootdev && thisino == rootino))
>>
>>    since the rootfs (/) is bind mounted onto the directory and the flow
>>    goes on to line 449, where it puts a '/' in the byte before the
>>    buffer.
>>
>> - Finally on line 458, it moves 2 bytes (the underflowed byte and the
>>    '\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
>>
>> - buf is returned on line 469 and errno is not set.
>>
>> This resolves BZ #28769.
>>
>> Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
>> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
> 
> Look good with just two fixed below for CMSG_DATA and a couple of comments.
> Ok with the fixes, the comments would be good but it is a blocker.
> 
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
> 
>> ---
>>   NEWS                                          |   6 +
>>   sysdeps/posix/getcwd.c                        |   7 +
>>   sysdeps/unix/sysv/linux/Makefile              |   7 +-
>>   .../unix/sysv/linux/tst-getcwd-smallbuff.c    | 245 ++++++++++++++++++
>>   4 files changed, 264 insertions(+), 1 deletion(-)
>>   create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
>>
>> diff --git a/NEWS b/NEWS
>> index 4c392a445e..07e9eac52d 100644
>> --- a/NEWS
>> +++ b/NEWS
>> @@ -170,6 +170,12 @@ Security related changes:
>>     function could result in a memory leak and potential access of
>>     uninitialized memory.  Reported by Qualys.
>>   
>> +  CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
>> +  function may result in an off-by-one buffer underflow and overflow
>> +  when the current working directory is longer than PATH_MAX and also
>> +  corresponds to the / directory through an unprivileged mount
>> +  namespace.  Reported by Qualys.
>> +
>>   The following bugs are resolved with this release:
>>   
>>     [The release manager will add the list generated by
>> diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
>> index e147a31a81..9d5787b6f4 100644
>> --- a/sysdeps/posix/getcwd.c
>> +++ b/sysdeps/posix/getcwd.c
>> @@ -187,6 +187,13 @@ __getcwd_generic (char *buf, size_t size)
>>     size_t allocated = size;
>>     size_t used;
>>   
>> +  /* A size of 1 byte is never useful.  */
>> +  if (allocated == 1)
>> +    {
>> +      __set_errno (ERANGE);
>> +      return NULL;
>> +    }
>> +
>>   #if HAVE_MINIMALLY_WORKING_GETCWD
>>     /* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
>>        this is much slower than the system getcwd (at least on
>> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
>> index 85fc8cbf75..7ca9350c99 100644
>> --- a/sysdeps/unix/sysv/linux/Makefile
>> +++ b/sysdeps/unix/sysv/linux/Makefile
>> @@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
>>   
>>   sysdep_headers += bits/fcntl-linux.h
>>   
>> -tests += tst-fallocate tst-fallocate64 tst-o_path-locks
>> +tests += \
>> +  tst-fallocate \
>> +  tst-fallocate64 \
>> +  tst-getcwd-smallbuff \
>> +  tst-o_path-locks \
>> +# tests
>>   endif
>>   
>>   ifeq ($(subdir),elf)
>> diff --git a/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
>> new file mode 100644
>> index 0000000000..791dfe4d02
>> --- /dev/null
>> +++ b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
>> @@ -0,0 +1,245 @@
>> +/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
>> +   buffer when the CWD is too long and is also a mount target of /.  See bug
>> +   #28769 or CVE-2021-3999 for more context.
>> +   Copyright The GNU Toolchain Authors.
>> +   This file is part of the GNU C Library.
>> +
>> +   The GNU C Library is free software; you can redistribute it and/or
>> +   modify it under the terms of the GNU Lesser General Public
>> +   License as published by the Free Software Foundation; either
>> +   version 2.1 of the License, or (at your option) any later version.
>> +
>> +   The GNU C Library is distributed in the hope that it will be useful,
>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> +   Lesser General Public License for more details.
>> +
>> +   You should have received a copy of the GNU Lesser General Public
>> +   License along with the GNU C Library; if not, see
>> +   <https://www.gnu.org/licenses/>.  */
>> +
>> +#include <errno.h>
>> +#include <fcntl.h>
>> +#include <limits.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <string.h>
>> +#include <sys/mount.h>
>> +#include <sys/stat.h>
>> +#include <sys/types.h>
>> +#include <sys/wait.h>
>> +
>> +#include <sys/socket.h>
>> +#include <sys/un.h>
>> +#include <support/check.h>
>> +#include <support/temp_file.h>
>> +#include <support/xsched.h>
>> +#include <support/xunistd.h>
>> +
>> +#ifndef PATH_MAX
>> +# define PATH_MAX 1024
>> +#endif
> 
> No need since it is a Linux only test and PATH_MAX is always defined.

Ahh, I didn't actually need it anyway, leftover from a previous 
iteration.  I'll remove it.

> 
>> +
>> +static char *base;
>> +#define BASENAME "tst-getcwd-smallbuff"
>> +#define MOUNT_NAME "mpoint"
>> +static int sockfd[2];
>> +
>> +static void
>> +do_cleanup (void)
>> +{
>> +  support_chdir_toolong_temp_directory (base);
>> +  TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
>> +  free (base);
>> +}
>> +
>> +static void
>> +send_fd (const int sock, const int fd)
>> +{
>> +  struct msghdr msg;
>> +  union
>> +    {
>> +      struct cmsghdr hdr;
>> +      char buf[CMSG_SPACE (sizeof (int))];
>> +    } cmsgbuf;
> 
> Maybe zero-initialize both first to avoid the memset below?

OK.

> 
>> +  struct cmsghdr *cmsg;
>> +  struct iovec vec;
>> +  char ch = 'A';
>> +  ssize_t n;
>> +
>> +  memset (&msg, 0, sizeof (msg));
>> +  memset (&cmsgbuf, 0, sizeof (cmsgbuf));
>> +  msg.msg_control = &cmsgbuf.buf;
>> +  msg.msg_controllen = sizeof (cmsgbuf.buf);
>> +
>> +  cmsg = CMSG_FIRSTHDR (&msg);
>> +  cmsg->cmsg_len = CMSG_LEN (sizeof (int));
>> +  cmsg->cmsg_level = SOL_SOCKET;
>> +  cmsg->cmsg_type = SCM_RIGHTS;
>> +  *(int *) CMSG_DATA (cmsg) = fd;
> 
> I think CMSG_DATA does not guarantee the alignment, so I think it would be
> safe to use memcpy here:
> 
>    memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));

OK.

> 
>> +
>> +  vec.iov_base = &ch;
>> +  vec.iov_len = 1;
>> +  msg.msg_iov = &vec;
>> +  msg.msg_iovlen = 1;
>> +
>> +  while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
>> +
>> +  TEST_VERIFY_EXIT (n == 1);
>> +}
>> +
> 
> Ok.
> 
>> +static int
>> +recv_fd (const int sock)
>> +{
>> +  struct msghdr msg;
> 
> Maybe also zero-initialize here.
> 
>> +  union
>> +    {
>> +      struct cmsghdr hdr;
>> +      char buf[CMSG_SPACE(sizeof(int))];
>> +    } cmsgbuf;
>> +  struct cmsghdr *cmsg;
>> +  struct iovec vec;
>> +  ssize_t n;
>> +  char ch = '\0';
>> +  int fd = -1;
>> +
>> +  memset (&msg, 0, sizeof (msg));
>> +  vec.iov_base = &ch;
>> +  vec.iov_len = 1;
>> +  msg.msg_iov = &vec;
>> +  msg.msg_iovlen = 1;
>> +
>> +  memset (&cmsgbuf, 0, sizeof (cmsgbuf));
>> +  msg.msg_control = &cmsgbuf.buf;
>> +  msg.msg_controllen = sizeof (cmsgbuf.buf);
>> +
>> +  while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
>> +  if (n != 1 || ch != 'A')
>> +    return -1;
>> +
>> +  cmsg = CMSG_FIRSTHDR (&msg);
>> +  if (cmsg == NULL)
>> +    return -1;
>> +  if (cmsg->cmsg_type != SCM_RIGHTS)
>> +    return -1;
>> +  fd = *(const int *) CMSG_DATA (cmsg);
> 
> Same as before, I think you will need to copy to a temporary using memcpy.

Why not just:

     memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));

i.e., is a temporary necessary?

> 
>> +  if (fd < 0)
>> +    return -1;
>> +  return fd;
>> +}
>> +
>> +static int
>> +child_func (void * const arg)
>> +{
>> +  xclose (sockfd[0]);
>> +  const int sock = sockfd[1];
>> +  char ch;
>> +
>> +  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
>> +  TEST_VERIFY_EXIT (ch == '1');
>> +
>> +  if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
>> +    FAIL_EXIT1 ("mount failed: %m\n");
>> +  const int fd = xopen ("mpoint",
>> +			O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
>> +
>> +  send_fd (sock, fd);
>> +  xclose (fd);
>> +
>> +  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
>> +  TEST_VERIFY_EXIT (ch == 'a');
>> +
>> +  xclose (sock);
>> +  return 0;
>> +}
>> +
>> +static void
>> +update_map (char * const mapping, const char * const map_file)
>> +{
>> +  const size_t map_len = strlen (mapping);
>> +
>> +  const int fd = xopen (map_file, O_WRONLY, 0);
>> +  xwrite (fd, mapping, map_len);
>> +  xclose (fd);
>> +}
>> +
>> +static void
>> +proc_setgroups_write (const long child_pid, const char * const str)
>> +{
>> +  const size_t str_len = strlen(str);
>> +
>> +  char setgroups_path[64];
> 
> 
> Maybe define the size as:
> 
>    /* The path is the form /proc/%ld/setgroups.  */
>    char map_path[sizeof("/proc/setgroups") + INT_STRLEN_BOUND (long int)];
> 

OK.

>> +  snprintf (setgroups_path, sizeof (setgroups_path),
>> +	    "/proc/%ld/setgroups", child_pid);
>> +
>> +  const int fd = open (setgroups_path, O_WRONLY);
>> +
>> +  if (fd < 0)
>> +    {
>> +      TEST_VERIFY_EXIT (errno == ENOENT);
>> +      FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
>> +    }
>> +
>> +  xwrite (fd, str, str_len);
>> +  xclose(fd);
>> +}
>> +
>> +static char child_stack[1024 * 1024];
>> +
>> +int
>> +do_test (void)
>> +{
>> +  base = support_create_and_chdir_toolong_temp_directory (BASENAME);
>> +
>> +  xmkdir (MOUNT_NAME, S_IRWXU);
>> +  atexit (do_cleanup);
>> +
>> +  TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
>> +  pid_t child_pid = xclone (child_func, NULL, child_stack,
>> +			    sizeof (child_stack),
>> +			    CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
>> +
>> +  xclose (sockfd[1]);
>> +  const int sock = sockfd[0];
>> +
>> +  char map_path[64], map_buf[64];
> 
> Same comment as for setgroups_path.
> 
>> +  snprintf (map_path, sizeof (map_path),  ,
>> +	    (long) child_pid);
>> +  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
>> +  update_map (map_buf, map_path);
>> +
>> +  proc_setgroups_write ((long) child_pid, "deny");
>> +  snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
>> +	    (long) child_pid);
>> +  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
>> +  update_map (map_buf, map_path);
>> +
>> +  TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
>> +  const int fd = recv_fd (sock);
>> +  TEST_VERIFY_EXIT (fd >= 0);
>> +  TEST_VERIFY_EXIT (fchdir (fd) == 0);
>> +
>> +  static char buf[2 * 10 + 1];
>> +  memset (buf, 'A', sizeof(buf));
> 
> 
> Space before (.
> 
>> +
>> +  /* Finally, call getcwd and check if it resulted in a buffer underflow.  */
>> +  char * cwd = getcwd (buf + sizeof(buf) / 2, 1);
>> +  TEST_VERIFY (cwd == NULL);
>> +  TEST_VERIFY (errno == ERANGE);
>> +
>> +  for (int i = 0; i < sizeof (buf); i++)
>> +    if (buf[i] != 'A')
>> +      {
>> +	printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
>> +	support_record_failure ();
>> +      }
>> +
>> +  TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
>> +  xclose (sock);
>> +  TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
>> +
>> +  return 0;
>> +}
>> +
>> +#define CLEANUP_HANDLER do_cleanup
>> +#include <support/test-driver.c>
> 

Re: [PATCH v3 3/3] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Adhemerval Zanella]

On 21/01/2022 14:26, Siddhesh Poyarekar wrote:
> On 21/01/2022 22:11, Adhemerval Zanella wrote:
>>
>>
>> On 20/01/2022 06:32, Siddhesh Poyarekar wrote:
>>> +  cmsg = CMSG_FIRSTHDR (&msg);
>>> +  if (cmsg == NULL)
>>> +    return -1;
>>> +  if (cmsg->cmsg_type != SCM_RIGHTS)
>>> +    return -1;
>>> +  fd = *(const int *) CMSG_DATA (cmsg);
>>
>> Same as before, I think you will need to copy to a temporary using memcpy.
> 
> Why not just:
> 
>     memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
> 
> i.e., is a temporary necessary?

Not really, the above works just fine.

[PATCH v4] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Siddhesh Poyarekar]

Fixed up, I'll push this if there are no further issues.

Thanks,
Siddhesh

-->8--

No valid path returned by getcwd would fit into 1 byte, so reject the
size early and return NULL with errno set to ERANGE.  This change is
prompted by CVE-2021-3999, which describes a single byte buffer
underflow and overflow when all of the following conditions are met:

- The buffer size (i.e. the second argument of getcwd) is 1 byte
- The current working directory is too long
- '/' is also mounted on the current working directory

Sequence of events:

- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
  because the linux kernel checks for name length before it checks
  buffer size

- The code falls back to the generic getcwd in sysdeps/posix

- In the generic func, the buf[0] is set to '\0' on line 250

- this while loop on line 262 is bypassed:

    while (!(thisdev == rootdev && thisino == rootino))

  since the rootfs (/) is bind mounted onto the directory and the flow
  goes on to line 449, where it puts a '/' in the byte before the
  buffer.

- Finally on line 458, it moves 2 bytes (the underflowed byte and the
  '\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.

- buf is returned on line 469 and errno is not set.

This resolves BZ #28769.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 NEWS                                          |   6 +
 sysdeps/posix/getcwd.c                        |   7 +
 sysdeps/unix/sysv/linux/Makefile              |   7 +-
 .../unix/sysv/linux/tst-getcwd-smallbuff.c    | 243 ++++++++++++++++++
 4 files changed, 262 insertions(+), 1 deletion(-)
 create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c

diff --git a/NEWS b/NEWS
index 4c392a445e..07e9eac52d 100644
--- a/NEWS
+++ b/NEWS
@@ -170,6 +170,12 @@ Security related changes:
   function could result in a memory leak and potential access of
   uninitialized memory.  Reported by Qualys.
 
+  CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
+  function may result in an off-by-one buffer underflow and overflow
+  when the current working directory is longer than PATH_MAX and also
+  corresponds to the / directory through an unprivileged mount
+  namespace.  Reported by Qualys.
+
 The following bugs are resolved with this release:
 
   [The release manager will add the list generated by
diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
index e147a31a81..9d5787b6f4 100644
--- a/sysdeps/posix/getcwd.c
+++ b/sysdeps/posix/getcwd.c
@@ -187,6 +187,13 @@ __getcwd_generic (char *buf, size_t size)
   size_t allocated = size;
   size_t used;
 
+  /* A size of 1 byte is never useful.  */
+  if (allocated == 1)
+    {
+      __set_errno (ERANGE);
+      return NULL;
+    }
+
 #if HAVE_MINIMALLY_WORKING_GETCWD
   /* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
      this is much slower than the system getcwd (at least on
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 85fc8cbf75..7ca9350c99 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
 
 sysdep_headers += bits/fcntl-linux.h
 
-tests += tst-fallocate tst-fallocate64 tst-o_path-locks
+tests += \
+  tst-fallocate \
+  tst-fallocate64 \
+  tst-getcwd-smallbuff \
+  tst-o_path-locks \
+# tests
 endif
 
 ifeq ($(subdir),elf)
diff --git a/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
new file mode 100644
index 0000000000..212f9b94f3
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
@@ -0,0 +1,243 @@
+/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
+   buffer when the CWD is too long and is also a mount target of /.  See bug
+   #28769 or CVE-2021-3999 for more context.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <intprops.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <support/xsched.h>
+#include <support/xunistd.h>
+
+static char *base;
+#define BASENAME "tst-getcwd-smallbuff"
+#define MOUNT_NAME "mpoint"
+static int sockfd[2];
+
+static void
+do_cleanup (void)
+{
+  support_chdir_toolong_temp_directory (base);
+  TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
+  free (base);
+}
+
+static void
+send_fd (const int sock, const int fd)
+{
+  struct msghdr msg = {0};
+  union
+    {
+      struct cmsghdr hdr;
+      char buf[CMSG_SPACE (sizeof (int))];
+    } cmsgbuf = {0};
+  struct cmsghdr *cmsg;
+  struct iovec vec;
+  char ch = 'A';
+  ssize_t n;
+
+  msg.msg_control = &cmsgbuf.buf;
+  msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+  cmsg = CMSG_FIRSTHDR (&msg);
+  cmsg->cmsg_len = CMSG_LEN (sizeof (int));
+  cmsg->cmsg_level = SOL_SOCKET;
+  cmsg->cmsg_type = SCM_RIGHTS;
+  memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
+
+  vec.iov_base = &ch;
+  vec.iov_len = 1;
+  msg.msg_iov = &vec;
+  msg.msg_iovlen = 1;
+
+  while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+
+  TEST_VERIFY_EXIT (n == 1);
+}
+
+static int
+recv_fd (const int sock)
+{
+  struct msghdr msg;
+  union
+    {
+      struct cmsghdr hdr;
+      char buf[CMSG_SPACE(sizeof(int))];
+    } cmsgbuf;
+  struct cmsghdr *cmsg;
+  struct iovec vec;
+  ssize_t n;
+  char ch = '\0';
+  int fd = -1;
+
+  memset (&msg, 0, sizeof (msg));
+  vec.iov_base = &ch;
+  vec.iov_len = 1;
+  msg.msg_iov = &vec;
+  msg.msg_iovlen = 1;
+
+  memset (&cmsgbuf, 0, sizeof (cmsgbuf));
+  msg.msg_control = &cmsgbuf.buf;
+  msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+  while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+  if (n != 1 || ch != 'A')
+    return -1;
+
+  cmsg = CMSG_FIRSTHDR (&msg);
+  if (cmsg == NULL)
+    return -1;
+  if (cmsg->cmsg_type != SCM_RIGHTS)
+    return -1;
+  memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
+  if (fd < 0)
+    return -1;
+  return fd;
+}
+
+static int
+child_func (void * const arg)
+{
+  xclose (sockfd[0]);
+  const int sock = sockfd[1];
+  char ch;
+
+  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+  TEST_VERIFY_EXIT (ch == '1');
+
+  if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
+    FAIL_EXIT1 ("mount failed: %m\n");
+  const int fd = xopen ("mpoint",
+			O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
+
+  send_fd (sock, fd);
+  xclose (fd);
+
+  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+  TEST_VERIFY_EXIT (ch == 'a');
+
+  xclose (sock);
+  return 0;
+}
+
+static void
+update_map (char * const mapping, const char * const map_file)
+{
+  const size_t map_len = strlen (mapping);
+
+  const int fd = xopen (map_file, O_WRONLY, 0);
+  xwrite (fd, mapping, map_len);
+  xclose (fd);
+}
+
+static void
+proc_setgroups_write (const long child_pid, const char * const str)
+{
+  const size_t str_len = strlen(str);
+
+  char setgroups_path[sizeof ("/proc//setgroups") + INT_STRLEN_BOUND (long)];
+
+  snprintf (setgroups_path, sizeof (setgroups_path),
+	    "/proc/%ld/setgroups", child_pid);
+
+  const int fd = open (setgroups_path, O_WRONLY);
+
+  if (fd < 0)
+    {
+      TEST_VERIFY_EXIT (errno == ENOENT);
+      FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
+    }
+
+  xwrite (fd, str, str_len);
+  xclose(fd);
+}
+
+static char child_stack[1024 * 1024];
+
+int
+do_test (void)
+{
+  base = support_create_and_chdir_toolong_temp_directory (BASENAME);
+
+  xmkdir (MOUNT_NAME, S_IRWXU);
+  atexit (do_cleanup);
+
+  TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
+  pid_t child_pid = xclone (child_func, NULL, child_stack,
+			    sizeof (child_stack),
+			    CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
+
+  xclose (sockfd[1]);
+  const int sock = sockfd[0];
+
+  char map_path[sizeof ("/proc//uid_map") + INT_STRLEN_BOUND (long)];
+  char map_buf[sizeof ("0  1") + INT_STRLEN_BOUND (long)];
+
+  snprintf (map_path, sizeof (map_path), "/proc/%ld/uid_map",
+	    (long) child_pid);
+  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
+  update_map (map_buf, map_path);
+
+  proc_setgroups_write ((long) child_pid, "deny");
+  snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
+	    (long) child_pid);
+  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
+  update_map (map_buf, map_path);
+
+  TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
+  const int fd = recv_fd (sock);
+  TEST_VERIFY_EXIT (fd >= 0);
+  TEST_VERIFY_EXIT (fchdir (fd) == 0);
+
+  static char buf[2 * 10 + 1];
+  memset (buf, 'A', sizeof (buf));
+
+  /* Finally, call getcwd and check if it resulted in a buffer underflow.  */
+  char * cwd = getcwd (buf + sizeof (buf) / 2, 1);
+  TEST_VERIFY (cwd == NULL);
+  TEST_VERIFY (errno == ERANGE);
+
+  for (int i = 0; i < sizeof (buf); i++)
+    if (buf[i] != 'A')
+      {
+	printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
+	support_record_failure ();
+      }
+
+  TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
+  xclose (sock);
+  TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
+
+  return 0;
+}
+
+#define CLEANUP_HANDLER do_cleanup
+#include <support/test-driver.c>
-- 
2.34.1

Re: [PATCH v4] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Andreas Schwab]

On Jan 21 2022, Siddhesh Poyarekar via Libc-alpha wrote:

> +static int
> +recv_fd (const int sock)
> +{
> +  struct msghdr msg;
> +  union
> +    {
> +      struct cmsghdr hdr;
> +      char buf[CMSG_SPACE(sizeof(int))];
> +    } cmsgbuf;

Zero-init like in send_fd.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: [PATCH v4] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Siddhesh Poyarekar]

On 21/01/2022 23:29, Andreas Schwab wrote:
> On Jan 21 2022, Siddhesh Poyarekar via Libc-alpha wrote:
> 
>> +static int
>> +recv_fd (const int sock)
>> +{
>> +  struct msghdr msg;
>> +  union
>> +    {
>> +      struct cmsghdr hdr;
>> +      char buf[CMSG_SPACE(sizeof(int))];
>> +    } cmsgbuf;
> 
> Zero-init like in send_fd.
> 

Thanks, I missed that.  Sending v5.

Siddhesh

[PATCH v5] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Siddhesh Poyarekar]

No valid path returned by getcwd would fit into 1 byte, so reject the
size early and return NULL with errno set to ERANGE.  This change is
prompted by CVE-2021-3999, which describes a single byte buffer
underflow and overflow when all of the following conditions are met:

- The buffer size (i.e. the second argument of getcwd) is 1 byte
- The current working directory is too long
- '/' is also mounted on the current working directory

Sequence of events:

- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
  because the linux kernel checks for name length before it checks
  buffer size

- The code falls back to the generic getcwd in sysdeps/posix

- In the generic func, the buf[0] is set to '\0' on line 250

- this while loop on line 262 is bypassed:

    while (!(thisdev == rootdev && thisino == rootino))

  since the rootfs (/) is bind mounted onto the directory and the flow
  goes on to line 449, where it puts a '/' in the byte before the
  buffer.

- Finally on line 458, it moves 2 bytes (the underflowed byte and the
  '\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.

- buf is returned on line 469 and errno is not set.

This resolves BZ #28769.

Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 NEWS                                          |   6 +
 sysdeps/posix/getcwd.c                        |   7 +
 sysdeps/unix/sysv/linux/Makefile              |   7 +-
 .../unix/sysv/linux/tst-getcwd-smallbuff.c    | 241 ++++++++++++++++++
 4 files changed, 260 insertions(+), 1 deletion(-)
 create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c

diff --git a/NEWS b/NEWS
index 4c392a445e..07e9eac52d 100644
--- a/NEWS
+++ b/NEWS
@@ -170,6 +170,12 @@ Security related changes:
   function could result in a memory leak and potential access of
   uninitialized memory.  Reported by Qualys.
 
+  CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
+  function may result in an off-by-one buffer underflow and overflow
+  when the current working directory is longer than PATH_MAX and also
+  corresponds to the / directory through an unprivileged mount
+  namespace.  Reported by Qualys.
+
 The following bugs are resolved with this release:
 
   [The release manager will add the list generated by
diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
index e147a31a81..9d5787b6f4 100644
--- a/sysdeps/posix/getcwd.c
+++ b/sysdeps/posix/getcwd.c
@@ -187,6 +187,13 @@ __getcwd_generic (char *buf, size_t size)
   size_t allocated = size;
   size_t used;
 
+  /* A size of 1 byte is never useful.  */
+  if (allocated == 1)
+    {
+      __set_errno (ERANGE);
+      return NULL;
+    }
+
 #if HAVE_MINIMALLY_WORKING_GETCWD
   /* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
      this is much slower than the system getcwd (at least on
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 85fc8cbf75..7ca9350c99 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
 
 sysdep_headers += bits/fcntl-linux.h
 
-tests += tst-fallocate tst-fallocate64 tst-o_path-locks
+tests += \
+  tst-fallocate \
+  tst-fallocate64 \
+  tst-getcwd-smallbuff \
+  tst-o_path-locks \
+# tests
 endif
 
 ifeq ($(subdir),elf)
diff --git a/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
new file mode 100644
index 0000000000..d460d6e766
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
@@ -0,0 +1,241 @@
+/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
+   buffer when the CWD is too long and is also a mount target of /.  See bug
+   #28769 or CVE-2021-3999 for more context.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <intprops.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <support/xsched.h>
+#include <support/xunistd.h>
+
+static char *base;
+#define BASENAME "tst-getcwd-smallbuff"
+#define MOUNT_NAME "mpoint"
+static int sockfd[2];
+
+static void
+do_cleanup (void)
+{
+  support_chdir_toolong_temp_directory (base);
+  TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
+  free (base);
+}
+
+static void
+send_fd (const int sock, const int fd)
+{
+  struct msghdr msg = {0};
+  union
+    {
+      struct cmsghdr hdr;
+      char buf[CMSG_SPACE (sizeof (int))];
+    } cmsgbuf = {0};
+  struct cmsghdr *cmsg;
+  struct iovec vec;
+  char ch = 'A';
+  ssize_t n;
+
+  msg.msg_control = &cmsgbuf.buf;
+  msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+  cmsg = CMSG_FIRSTHDR (&msg);
+  cmsg->cmsg_len = CMSG_LEN (sizeof (int));
+  cmsg->cmsg_level = SOL_SOCKET;
+  cmsg->cmsg_type = SCM_RIGHTS;
+  memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
+
+  vec.iov_base = &ch;
+  vec.iov_len = 1;
+  msg.msg_iov = &vec;
+  msg.msg_iovlen = 1;
+
+  while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+
+  TEST_VERIFY_EXIT (n == 1);
+}
+
+static int
+recv_fd (const int sock)
+{
+  struct msghdr msg = {0};
+  union
+    {
+      struct cmsghdr hdr;
+      char buf[CMSG_SPACE(sizeof(int))];
+    } cmsgbuf = {0};
+  struct cmsghdr *cmsg;
+  struct iovec vec;
+  ssize_t n;
+  char ch = '\0';
+  int fd = -1;
+
+  vec.iov_base = &ch;
+  vec.iov_len = 1;
+  msg.msg_iov = &vec;
+  msg.msg_iovlen = 1;
+
+  msg.msg_control = &cmsgbuf.buf;
+  msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+  while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+  if (n != 1 || ch != 'A')
+    return -1;
+
+  cmsg = CMSG_FIRSTHDR (&msg);
+  if (cmsg == NULL)
+    return -1;
+  if (cmsg->cmsg_type != SCM_RIGHTS)
+    return -1;
+  memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
+  if (fd < 0)
+    return -1;
+  return fd;
+}
+
+static int
+child_func (void * const arg)
+{
+  xclose (sockfd[0]);
+  const int sock = sockfd[1];
+  char ch;
+
+  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+  TEST_VERIFY_EXIT (ch == '1');
+
+  if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
+    FAIL_EXIT1 ("mount failed: %m\n");
+  const int fd = xopen ("mpoint",
+			O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
+
+  send_fd (sock, fd);
+  xclose (fd);
+
+  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+  TEST_VERIFY_EXIT (ch == 'a');
+
+  xclose (sock);
+  return 0;
+}
+
+static void
+update_map (char * const mapping, const char * const map_file)
+{
+  const size_t map_len = strlen (mapping);
+
+  const int fd = xopen (map_file, O_WRONLY, 0);
+  xwrite (fd, mapping, map_len);
+  xclose (fd);
+}
+
+static void
+proc_setgroups_write (const long child_pid, const char * const str)
+{
+  const size_t str_len = strlen(str);
+
+  char setgroups_path[sizeof ("/proc//setgroups") + INT_STRLEN_BOUND (long)];
+
+  snprintf (setgroups_path, sizeof (setgroups_path),
+	    "/proc/%ld/setgroups", child_pid);
+
+  const int fd = open (setgroups_path, O_WRONLY);
+
+  if (fd < 0)
+    {
+      TEST_VERIFY_EXIT (errno == ENOENT);
+      FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
+    }
+
+  xwrite (fd, str, str_len);
+  xclose(fd);
+}
+
+static char child_stack[1024 * 1024];
+
+int
+do_test (void)
+{
+  base = support_create_and_chdir_toolong_temp_directory (BASENAME);
+
+  xmkdir (MOUNT_NAME, S_IRWXU);
+  atexit (do_cleanup);
+
+  TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
+  pid_t child_pid = xclone (child_func, NULL, child_stack,
+			    sizeof (child_stack),
+			    CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
+
+  xclose (sockfd[1]);
+  const int sock = sockfd[0];
+
+  char map_path[sizeof ("/proc//uid_map") + INT_STRLEN_BOUND (long)];
+  char map_buf[sizeof ("0  1") + INT_STRLEN_BOUND (long)];
+
+  snprintf (map_path, sizeof (map_path), "/proc/%ld/uid_map",
+	    (long) child_pid);
+  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
+  update_map (map_buf, map_path);
+
+  proc_setgroups_write ((long) child_pid, "deny");
+  snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
+	    (long) child_pid);
+  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
+  update_map (map_buf, map_path);
+
+  TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
+  const int fd = recv_fd (sock);
+  TEST_VERIFY_EXIT (fd >= 0);
+  TEST_VERIFY_EXIT (fchdir (fd) == 0);
+
+  static char buf[2 * 10 + 1];
+  memset (buf, 'A', sizeof (buf));
+
+  /* Finally, call getcwd and check if it resulted in a buffer underflow.  */
+  char * cwd = getcwd (buf + sizeof (buf) / 2, 1);
+  TEST_VERIFY (cwd == NULL);
+  TEST_VERIFY (errno == ERANGE);
+
+  for (int i = 0; i < sizeof (buf); i++)
+    if (buf[i] != 'A')
+      {
+	printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
+	support_record_failure ();
+      }
+
+  TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
+  xclose (sock);
+  TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
+
+  return 0;
+}
+
+#define CLEANUP_HANDLER do_cleanup
+#include <support/test-driver.c>
-- 
2.34.1

Re: [PATCH v5] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)

[Siddhesh Poyarekar]

On 21/01/2022 23:34, Siddhesh Poyarekar via Libc-alpha wrote:
> No valid path returned by getcwd would fit into 1 byte, so reject the
> size early and return NULL with errno set to ERANGE.  This change is
> prompted by CVE-2021-3999, which describes a single byte buffer
> underflow and overflow when all of the following conditions are met:
> 
> - The buffer size (i.e. the second argument of getcwd) is 1 byte
> - The current working directory is too long
> - '/' is also mounted on the current working directory
> 
> Sequence of events:
> 
> - In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
>    because the linux kernel checks for name length before it checks
>    buffer size
> 
> - The code falls back to the generic getcwd in sysdeps/posix
> 
> - In the generic func, the buf[0] is set to '\0' on line 250
> 
> - this while loop on line 262 is bypassed:
> 
>      while (!(thisdev == rootdev && thisino == rootino))
> 
>    since the rootfs (/) is bind mounted onto the directory and the flow
>    goes on to line 449, where it puts a '/' in the byte before the
>    buffer.
> 
> - Finally on line 458, it moves 2 bytes (the underflowed byte and the
>    '\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
> 
> - buf is returned on line 469 and errno is not set.
> 
> This resolves BZ #28769.
> 
> Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
> Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

Pushed now since updates were trivial and Adhemerval and Andreas had 
already acked the rest.

Thanks,
Siddhesh

> ---
>   NEWS                                          |   6 +
>   sysdeps/posix/getcwd.c                        |   7 +
>   sysdeps/unix/sysv/linux/Makefile              |   7 +-
>   .../unix/sysv/linux/tst-getcwd-smallbuff.c    | 241 ++++++++++++++++++
>   4 files changed, 260 insertions(+), 1 deletion(-)
>   create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
> 
> diff --git a/NEWS b/NEWS
> index 4c392a445e..07e9eac52d 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -170,6 +170,12 @@ Security related changes:
>     function could result in a memory leak and potential access of
>     uninitialized memory.  Reported by Qualys.
>   
> +  CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
> +  function may result in an off-by-one buffer underflow and overflow
> +  when the current working directory is longer than PATH_MAX and also
> +  corresponds to the / directory through an unprivileged mount
> +  namespace.  Reported by Qualys.
> +
>   The following bugs are resolved with this release:
>   
>     [The release manager will add the list generated by
> diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
> index e147a31a81..9d5787b6f4 100644
> --- a/sysdeps/posix/getcwd.c
> +++ b/sysdeps/posix/getcwd.c
> @@ -187,6 +187,13 @@ __getcwd_generic (char *buf, size_t size)
>     size_t allocated = size;
>     size_t used;
>   
> +  /* A size of 1 byte is never useful.  */
> +  if (allocated == 1)
> +    {
> +      __set_errno (ERANGE);
> +      return NULL;
> +    }
> +
>   #if HAVE_MINIMALLY_WORKING_GETCWD
>     /* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
>        this is much slower than the system getcwd (at least on
> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> index 85fc8cbf75..7ca9350c99 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
>   
>   sysdep_headers += bits/fcntl-linux.h
>   
> -tests += tst-fallocate tst-fallocate64 tst-o_path-locks
> +tests += \
> +  tst-fallocate \
> +  tst-fallocate64 \
> +  tst-getcwd-smallbuff \
> +  tst-o_path-locks \
> +# tests
>   endif
>   
>   ifeq ($(subdir),elf)
> diff --git a/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
> new file mode 100644
> index 0000000000..d460d6e766
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
> @@ -0,0 +1,241 @@
> +/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
> +   buffer when the CWD is too long and is also a mount target of /.  See bug
> +   #28769 or CVE-2021-3999 for more context.
> +   Copyright The GNU Toolchain Authors.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <intprops.h>
> +#include <limits.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/mount.h>
> +#include <sys/stat.h>
> +#include <sys/types.h>
> +#include <sys/wait.h>
> +
> +#include <sys/socket.h>
> +#include <sys/un.h>
> +#include <support/check.h>
> +#include <support/temp_file.h>
> +#include <support/xsched.h>
> +#include <support/xunistd.h>
> +
> +static char *base;
> +#define BASENAME "tst-getcwd-smallbuff"
> +#define MOUNT_NAME "mpoint"
> +static int sockfd[2];
> +
> +static void
> +do_cleanup (void)
> +{
> +  support_chdir_toolong_temp_directory (base);
> +  TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
> +  free (base);
> +}
> +
> +static void
> +send_fd (const int sock, const int fd)
> +{
> +  struct msghdr msg = {0};
> +  union
> +    {
> +      struct cmsghdr hdr;
> +      char buf[CMSG_SPACE (sizeof (int))];
> +    } cmsgbuf = {0};
> +  struct cmsghdr *cmsg;
> +  struct iovec vec;
> +  char ch = 'A';
> +  ssize_t n;
> +
> +  msg.msg_control = &cmsgbuf.buf;
> +  msg.msg_controllen = sizeof (cmsgbuf.buf);
> +
> +  cmsg = CMSG_FIRSTHDR (&msg);
> +  cmsg->cmsg_len = CMSG_LEN (sizeof (int));
> +  cmsg->cmsg_level = SOL_SOCKET;
> +  cmsg->cmsg_type = SCM_RIGHTS;
> +  memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
> +
> +  vec.iov_base = &ch;
> +  vec.iov_len = 1;
> +  msg.msg_iov = &vec;
> +  msg.msg_iovlen = 1;
> +
> +  while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
> +
> +  TEST_VERIFY_EXIT (n == 1);
> +}
> +
> +static int
> +recv_fd (const int sock)
> +{
> +  struct msghdr msg = {0};
> +  union
> +    {
> +      struct cmsghdr hdr;
> +      char buf[CMSG_SPACE(sizeof(int))];
> +    } cmsgbuf = {0};
> +  struct cmsghdr *cmsg;
> +  struct iovec vec;
> +  ssize_t n;
> +  char ch = '\0';
> +  int fd = -1;
> +
> +  vec.iov_base = &ch;
> +  vec.iov_len = 1;
> +  msg.msg_iov = &vec;
> +  msg.msg_iovlen = 1;
> +
> +  msg.msg_control = &cmsgbuf.buf;
> +  msg.msg_controllen = sizeof (cmsgbuf.buf);
> +
> +  while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
> +  if (n != 1 || ch != 'A')
> +    return -1;
> +
> +  cmsg = CMSG_FIRSTHDR (&msg);
> +  if (cmsg == NULL)
> +    return -1;
> +  if (cmsg->cmsg_type != SCM_RIGHTS)
> +    return -1;
> +  memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
> +  if (fd < 0)
> +    return -1;
> +  return fd;
> +}
> +
> +static int
> +child_func (void * const arg)
> +{
> +  xclose (sockfd[0]);
> +  const int sock = sockfd[1];
> +  char ch;
> +
> +  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
> +  TEST_VERIFY_EXIT (ch == '1');
> +
> +  if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
> +    FAIL_EXIT1 ("mount failed: %m\n");
> +  const int fd = xopen ("mpoint",
> +			O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
> +
> +  send_fd (sock, fd);
> +  xclose (fd);
> +
> +  TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
> +  TEST_VERIFY_EXIT (ch == 'a');
> +
> +  xclose (sock);
> +  return 0;
> +}
> +
> +static void
> +update_map (char * const mapping, const char * const map_file)
> +{
> +  const size_t map_len = strlen (mapping);
> +
> +  const int fd = xopen (map_file, O_WRONLY, 0);
> +  xwrite (fd, mapping, map_len);
> +  xclose (fd);
> +}
> +
> +static void
> +proc_setgroups_write (const long child_pid, const char * const str)
> +{
> +  const size_t str_len = strlen(str);
> +
> +  char setgroups_path[sizeof ("/proc//setgroups") + INT_STRLEN_BOUND (long)];
> +
> +  snprintf (setgroups_path, sizeof (setgroups_path),
> +	    "/proc/%ld/setgroups", child_pid);
> +
> +  const int fd = open (setgroups_path, O_WRONLY);
> +
> +  if (fd < 0)
> +    {
> +      TEST_VERIFY_EXIT (errno == ENOENT);
> +      FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
> +    }
> +
> +  xwrite (fd, str, str_len);
> +  xclose(fd);
> +}
> +
> +static char child_stack[1024 * 1024];
> +
> +int
> +do_test (void)
> +{
> +  base = support_create_and_chdir_toolong_temp_directory (BASENAME);
> +
> +  xmkdir (MOUNT_NAME, S_IRWXU);
> +  atexit (do_cleanup);
> +
> +  TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
> +  pid_t child_pid = xclone (child_func, NULL, child_stack,
> +			    sizeof (child_stack),
> +			    CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
> +
> +  xclose (sockfd[1]);
> +  const int sock = sockfd[0];
> +
> +  char map_path[sizeof ("/proc//uid_map") + INT_STRLEN_BOUND (long)];
> +  char map_buf[sizeof ("0  1") + INT_STRLEN_BOUND (long)];
> +
> +  snprintf (map_path, sizeof (map_path), "/proc/%ld/uid_map",
> +	    (long) child_pid);
> +  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
> +  update_map (map_buf, map_path);
> +
> +  proc_setgroups_write ((long) child_pid, "deny");
> +  snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
> +	    (long) child_pid);
> +  snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
> +  update_map (map_buf, map_path);
> +
> +  TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
> +  const int fd = recv_fd (sock);
> +  TEST_VERIFY_EXIT (fd >= 0);
> +  TEST_VERIFY_EXIT (fchdir (fd) == 0);
> +
> +  static char buf[2 * 10 + 1];
> +  memset (buf, 'A', sizeof (buf));
> +
> +  /* Finally, call getcwd and check if it resulted in a buffer underflow.  */
> +  char * cwd = getcwd (buf + sizeof (buf) / 2, 1);
> +  TEST_VERIFY (cwd == NULL);
> +  TEST_VERIFY (errno == ERANGE);
> +
> +  for (int i = 0; i < sizeof (buf); i++)
> +    if (buf[i] != 'A')
> +      {
> +	printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
> +	support_record_failure ();
> +      }
> +
> +  TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
> +  xclose (sock);
> +  TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
> +
> +  return 0;
> +}
> +
> +#define CLEANUP_HANDLER do_cleanup
> +#include <support/test-driver.c>