Re: [PATCH v7] posix: Deprecate group_member for Linux

[Joe Simmons-Talbott <josimmon@redhat.com>]

Ping.

On Wed, Dec 13, 2023 at 10:29:25AM -0500, Joe Simmons-Talbott wrote:
> The alloca usage in group_member could lead to stack overflow on Linux.
> Removing the alloca usage would require group_member to handle the error
> condition where memory could not be allocated and that cannot be done
> since group_member returns a boolean value.  Thus deprecate group_member.
> Add an internal only implementation of __group_member2 using a
> scratch_buffer and return -1 for memory allocation errors.  Use
> __group_member2 for in place of __group_member internally.  Add testcases
> for both group_member and __group_member2.
> ---
> Changes to v6:
> * Use the intial scratch_buffer size as the starting point for
>   determining how much space is needed to store the group list.
> * Call getgroups() with a zero size and set the scratch_buffer size
>   based on the returned number of groups.
> 
> Changes to v5:
> * Add __group_member2 and use it internally in the place of the now
>   deprecated group_member.
> * Add a testcase for __group_member2.
> 
> Changes to v4:
> * Rebase onto latest commit.
> 
> Changes to v3:
> * Fix include guards to match file location _BITS_GROUP_MEMBER_H
> * Fix indentation of preprocessor directives
> 
> Changes to v2:
> * Move the linux group_member.h to the bits directory
> * Include the correct group_member.h in posix/unistd.h
> 
> Changes to v1:
> * Add NEWS entry
> * Move group_member.h to bits/group_member.h
> * Include bits/group_member.h in installed headers
> * Add tests to group_member.h files to only be included from unistd.h
>  NEWS                                        |  4 ++
>  bits/group_member.h                         | 31 +++++++++++++++
>  include/unistd.h                            |  1 +
>  posix/Makefile                              |  8 ++++
>  posix/group_member.c                        | 35 +++++++++++++++++
>  posix/tst-group_member.c                    | 41 ++++++++++++++++++++
>  posix/tst-group_member2.c                   | 43 +++++++++++++++++++++
>  posix/unistd.h                              |  6 +--
>  sysdeps/posix/euidaccess.c                  |  9 ++++-
>  sysdeps/unix/sysv/linux/bits/group_member.h | 32 +++++++++++++++
>  sysdeps/unix/sysv/linux/faccessat.c         |  8 +++-
>  11 files changed, 212 insertions(+), 6 deletions(-)
>  create mode 100644 bits/group_member.h
>  create mode 100644 posix/tst-group_member.c
>  create mode 100644 posix/tst-group_member2.c
>  create mode 100644 sysdeps/unix/sysv/linux/bits/group_member.h
> 
> diff --git a/NEWS b/NEWS
> index 3f0dee4fcc..032c5ff83d 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -68,6 +68,10 @@ Deprecated and removed features, and other changes affecting compatibility:
>    of GNU libc are advised to check whether their build processes can be
>    simplified.
>  
> +* Deprecated group_member on Linux as it uses alloca to allocate a large
> +  buffer and has no capability for indicating failure for other memory
> +  allocations.
> +
>  Changes to build and runtime requirements:
>  
>  * Building on LoongArch requires at a minimum binutils 2.41 for vector
> diff --git a/bits/group_member.h b/bits/group_member.h
> new file mode 100644
> index 0000000000..7c43e7ee06
> --- /dev/null
> +++ b/bits/group_member.h
> @@ -0,0 +1,31 @@
> +/* group_member declaration
> +   Copyright (C) 2023 Free Software Foundation, Inc.
> +   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/>.  */
> +
> +#ifndef _UNISTD_H
> +# error "Never use <bits/group_member.h> directly; include <unistd.h> instead."
> +#endif
> +
> +#ifndef _BITS_GROUP_MEMBER_H
> +# define _BITS_GROUP_MEMBER_H 1
> +
> +# ifdef	__USE_GNU
> +/* Return nonzero iff the calling process is in group GID.  */
> +extern int group_member (__gid_t __gid) __THROW;
> +# endif
> +
> +#endif /* _BITS_GROUP_MEMBER_H */
> diff --git a/include/unistd.h b/include/unistd.h
> index e241603b81..39d5bda372 100644
> --- a/include/unistd.h
> +++ b/include/unistd.h
> @@ -131,6 +131,7 @@ extern __gid_t __getegid (void) attribute_hidden;
>  extern int __getgroups (int __size, __gid_t __list[]) attribute_hidden;
>  libc_hidden_proto (__getpgid)
>  extern int __group_member (__gid_t __gid) attribute_hidden;
> +extern int __group_member2 (__gid_t __gid) attribute_hidden;
>  extern int __setuid (__uid_t __uid);
>  extern int __setreuid (__uid_t __ruid, __uid_t __euid);
>  extern int __setgid (__gid_t __gid);
> diff --git a/posix/Makefile b/posix/Makefile
> index 3ab124d040..c4948e3980 100644
> --- a/posix/Makefile
> +++ b/posix/Makefile
> @@ -29,6 +29,7 @@ headers := \
>    bits/getopt_core.h \
>    bits/getopt_ext.h \
>    bits/getopt_posix.h \
> +  bits/group_member.h \
>    bits/local_lim.h \
>    bits/mman_ext.h \
>    bits/posix1_lim.h \
> @@ -291,6 +292,7 @@ tests := \
>    tst-glob_symlinks \
>    tst-gnuglob \
>    tst-gnuglob64 \
> +  tst-group_member \
>    tst-mmap \
>    tst-mmap-offset \
>    tst-nanosleep \
> @@ -479,6 +481,10 @@ tests-special += \
>    # tests-special
>  endif
>  
> +# This test calls __group_member2 directly, which is not exported from glibc.
> +tests-internal += tst-group_member2
> +tests-static += tst-group_member2
> +
>  include ../Rules
>  
>  ifeq ($(run-built-tests),yes)
> @@ -606,6 +612,8 @@ bug-glob1-ARGS = "$(objpfx)"
>  tst-execvp3-ARGS = --test-dir=$(objpfx)
>  CFLAGS-tst-spawn3.c += -DOBJPFX=\"$(objpfx)\"
>  
> +CFLAGS-tst-group_member.c += -Wno-error=deprecated-declarations
> +
>  # Test voluntarily overflows struct dirent
>  CFLAGS-bug-glob2.c += $(no-fortify-source)
>  
> diff --git a/posix/group_member.c b/posix/group_member.c
> index 22422b1f9f..deb8bb404b 100644
> --- a/posix/group_member.c
> +++ b/posix/group_member.c
> @@ -18,6 +18,7 @@
>  
>  #include <sys/types.h>
>  #include <unistd.h>
> +#include <scratch_buffer.h>
>  #include <stdlib.h>
>  #include <limits.h>
>  
> @@ -47,3 +48,37 @@ __group_member (gid_t gid)
>    return 0;
>  }
>  weak_alias (__group_member, group_member)
> +
> +int
> +__group_member2 (gid_t gid)
> +{
> +  int n;
> +  gid_t *groups;
> +  struct scratch_buffer sbuf;
> +  scratch_buffer_init (&sbuf);
> +  groups = sbuf.data;
> +
> +  do
> +    {
> +      n = __getgroups (0, NULL);
> +      if (n > sbuf.length)
> +	{
> +	  if (!scratch_buffer_set_array_size (&sbuf, sizeof (*groups), n))
> +	    return -1;
> +	  groups = sbuf.data;
> +	}
> +
> +      n = __getgroups (n, groups);
> +    }
> +  while (n > sbuf.length);
> +
> +  while (n-- > 0)
> +    if (groups[n] == gid)
> +      {
> +	scratch_buffer_free (&sbuf);
> +        return 1;
> +      }
> +
> +  scratch_buffer_free (&sbuf);
> +  return 0;
> +}
> diff --git a/posix/tst-group_member.c b/posix/tst-group_member.c
> new file mode 100644
> index 0000000000..7f70841832
> --- /dev/null
> +++ b/posix/tst-group_member.c
> @@ -0,0 +1,41 @@
> +/* Basic tests for group_member.
> +   Copyright (C) 2023 Free Software Foundation, Inc.
> +   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 <alloca.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +
> +#include <support/check.h>
> +
> +static int do_test (void)
> +{
> +  int n;
> +  gid_t *groups;
> +
> +  n = getgroups (0, NULL);
> +  groups = alloca (n * sizeof (*groups));
> +  n = getgroups (n, groups);
> +
> +  while (n-- > 0)
> +    TEST_COMPARE (1, group_member(groups[n]));
> +
> +  return EXIT_SUCCESS;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/posix/tst-group_member2.c b/posix/tst-group_member2.c
> new file mode 100644
> index 0000000000..ee448c578a
> --- /dev/null
> +++ b/posix/tst-group_member2.c
> @@ -0,0 +1,43 @@
> +/* Basic tests for group_member.
> +   Copyright (C) 2023 Free Software Foundation, Inc.
> +   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 <alloca.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <posix/unistd.h>
> +
> +#include <support/check.h>
> +
> +extern int __group_member2 (__gid_t __gid);
> +
> +static int do_test (void)
> +{
> +  int n;
> +  gid_t *groups;
> +
> +  n = getgroups (0, NULL);
> +  groups = alloca (n * sizeof (*groups));
> +  n = getgroups (n, groups);
> +
> +  while (n-- > 0)
> +    TEST_COMPARE (1, __group_member2(groups[n]));
> +
> +  return EXIT_SUCCESS;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/posix/unistd.h b/posix/unistd.h
> index 5b91ad4aaa..ccc55bb501 100644
> --- a/posix/unistd.h
> +++ b/posix/unistd.h
> @@ -710,10 +710,10 @@ extern __gid_t getegid (void) __THROW;
>     of its supplementary groups in LIST and return the number written.  */
>  extern int getgroups (int __size, __gid_t __list[]) __THROW __wur
>      __fortified_attr_access (__write_only__, 2, 1);
> +
>  #ifdef	__USE_GNU
> -/* Return nonzero iff the calling process is in group GID.  */
> -extern int group_member (__gid_t __gid) __THROW;
> -#endif
> +# include <bits/group_member.h>
> +#endif 
>  
>  /* Set the user ID of the calling process to UID.
>     If the calling process is the super-user, set the real
> diff --git a/sysdeps/posix/euidaccess.c b/sysdeps/posix/euidaccess.c
> index 2282a0a8dd..2eb9db4c95 100644
> --- a/sysdeps/posix/euidaccess.c
> +++ b/sysdeps/posix/euidaccess.c
> @@ -81,7 +81,7 @@ extern int errno;
>  
>  #ifdef _LIBC
>  
> -# define group_member __group_member
> +# define group_member __group_member2
>  # define euidaccess __euidaccess
>  
>  #else
> @@ -167,9 +167,14 @@ euidaccess (const char *path, int mode)
>  		    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
>      return 0;
>  
> +  int gm = group_member (stats.st_gid);
> +  if (euid != stats.st_uid && egid != stats.st_gid)
> +    if (gm == -1)
> +      return -1;
> +
>    if (euid == stats.st_uid)
>      granted = (unsigned int) (stats.st_mode & (mode << 6)) >> 6;
> -  else if (egid == stats.st_gid || group_member (stats.st_gid))
> +  else if (egid == stats.st_gid || gm)
>      granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
>    else
>      granted = (stats.st_mode & mode);
> diff --git a/sysdeps/unix/sysv/linux/bits/group_member.h b/sysdeps/unix/sysv/linux/bits/group_member.h
> new file mode 100644
> index 0000000000..0dd9505c76
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/bits/group_member.h
> @@ -0,0 +1,32 @@
> +/* group_member declaration
> +   Copyright (C) 2023 Free Software Foundation, Inc.
> +   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/>.  */
> +
> +#ifndef _UNISTD_H
> +# error "Never use <bits/group_member.h> directly; include <unistd.h> instead."
> +#endif
> +
> +#ifndef _BITS_GROUP_MEMBER_H
> +# define _BITS_GROUP_MEMBER_H 1
> +
> +# ifdef	__USE_GNU
> +/* Return nonzero iff the calling process is in group GID.  Deprecated */
> +extern int group_member (__gid_t __gid) __THROW
> +	__attribute_deprecated_msg__ ("may overflow the stack");
> +# endif
> +
> +#endif /* _BITS_GROUP_MEMBER_H */
> diff --git a/sysdeps/unix/sysv/linux/faccessat.c b/sysdeps/unix/sysv/linux/faccessat.c
> index 0ccbd778b5..f28ab0a6f4 100644
> --- a/sysdeps/unix/sysv/linux/faccessat.c
> +++ b/sysdeps/unix/sysv/linux/faccessat.c
> @@ -59,11 +59,17 @@ __faccessat (int fd, const char *file, int mode, int flag)
>  		   || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
>      return 0;
>  
> +  int gm = __group_member2 (stats.st_gid);
> +  if (uid != stats.st_uid &&
> +      (stats.st_gid != ((flag & AT_EACCESS) ? __getegid () : __getgid ())))
> +    if (gm == -1)
> +      return -1;
> +
>    int granted = (uid == stats.st_uid
>  		 ? (unsigned int) (stats.st_mode & (mode << 6)) >> 6
>  		 : (stats.st_gid == ((flag & AT_EACCESS)
>  				     ? __getegid () : __getgid ())
> -		    || __group_member (stats.st_gid))
> +		    || gm)
>  		 ? (unsigned int) (stats.st_mode & (mode << 3)) >> 3
>  		 : (stats.st_mode & mode));
>  
> -- 
> 2.41.0
>