* [2.26 COMMITTED] linux: make getcwd(3) fail if it cannot obtain an absolute path [BZ #22679]
@ 2018-01-01 0:00 Dmitry V. Levin
0 siblings, 0 replies; only message in thread
From: Dmitry V. Levin @ 2018-01-01 0:00 UTC (permalink / raw)
To: libc-stable
Currently getcwd(3) can succeed without returning an absolute path
because the underlying getcwd syscall, starting with linux commit
v2.6.36-rc1~96^2~2, may succeed without returning an absolute path.
This is a conformance issue because "The getcwd() function shall
place an absolute pathname of the current working directory
in the array pointed to by buf, and return buf".
This is also a security issue because a non-absolute path returned
by getcwd(3) causes a buffer underflow in realpath(3).
Fix this by checking the path returned by getcwd syscall and falling
back to generic_getcwd if the path is not absolute, effectively making
getcwd(3) fail with ENOENT. The error code is chosen for consistency
with the case when the current directory is unlinked.
[BZ #22679]
CVE-2018-1000001
* sysdeps/unix/sysv/linux/getcwd.c (__getcwd): Fall back to
generic_getcwd if the path returned by getcwd syscall is not absolute.
* io/tst-getcwd-abspath.c: New test.
* io/Makefile (tests): Add tst-getcwd-abspath.
(cherry picked from commit 52a713fdd0a30e1bd79818e2e3c4ab44ddca1a94)
---
ChangeLog | 9 ++++++
NEWS | 6 ++++
io/Makefile | 2 +-
io/tst-getcwd-abspath.c | 66 ++++++++++++++++++++++++++++++++++++++++
sysdeps/unix/sysv/linux/getcwd.c | 8 ++---
5 files changed, 86 insertions(+), 5 deletions(-)
create mode 100644 io/tst-getcwd-abspath.c
diff --git a/NEWS b/NEWS
index 003bf67..7f88e9e 100644
--- a/NEWS
+++ b/NEWS
@@ -59,6 +59,10 @@ Security related changes:
for AT_SECURE or SUID binaries could be used to load libraries from the
current directory.
+ CVE-2018-1000001: Buffer underflow in realpath function when getcwd function
+ succeeds without returning an absolute path due to unexpected behaviour
+ of the Linux kernel getcwd syscall. Reported by halfdog.
+
The following bugs are resolved with this release:
[16750] ldd: Never run file directly.
@@ -97,6 +101,8 @@ The following bugs are resolved with this release:
[22325] glibc: Memory leak in glob with GLOB_TILDE (CVE-2017-15671)
[22375] malloc returns pointer from tcache instead of NULL (CVE-2017-17426)
[22627] $ORIGIN in $LD_LIBRARY_PATH is substituted twice
+ [22679] getcwd(3) can succeed without returning an absolute path
+ (CVE-2018-1000001)
\f
Version 2.26
diff --git a/io/Makefile b/io/Makefile
index 2f26bf5..f0bdc83 100644
--- a/io/Makefile
+++ b/io/Makefile
@@ -70,7 +70,7 @@ tests := test-utime test-stat test-stat2 test-lfs tst-getcwd \
tst-symlinkat tst-linkat tst-readlinkat tst-mkdirat \
tst-mknodat tst-mkfifoat tst-ttyname_r bug-ftw5 \
tst-posix_fallocate tst-posix_fallocate64 \
- tst-fts tst-fts-lfs tst-open-tmpfile
+ tst-fts tst-fts-lfs tst-open-tmpfile tst-getcwd-abspath
ifeq ($(run-built-tests),yes)
tests-special += $(objpfx)ftwtest.out
diff --git a/io/tst-getcwd-abspath.c b/io/tst-getcwd-abspath.c
new file mode 100644
index 0000000..3a3636f
--- /dev/null
+++ b/io/tst-getcwd-abspath.c
@@ -0,0 +1,66 @@
+/* BZ #22679 getcwd(3) should not succeed without returning an absolute path.
+
+ Copyright (C) 2018 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 <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/test-driver.h>
+#include <support/xunistd.h>
+#include <unistd.h>
+
+static char *chroot_dir;
+
+/* The actual test. Run it in a subprocess, so that the test harness
+ can remove the temporary directory in --direct mode. */
+static void
+getcwd_callback (void *closure)
+{
+ xchroot (chroot_dir);
+
+ errno = 0;
+ char *cwd = getcwd (NULL, 0);
+ TEST_COMPARE (errno, ENOENT);
+ TEST_VERIFY (cwd == NULL);
+
+ errno = 0;
+ cwd = realpath (".", NULL);
+ TEST_COMPARE (errno, ENOENT);
+ TEST_VERIFY (cwd == NULL);
+
+ _exit (0);
+}
+
+static int
+do_test (void)
+{
+ support_become_root ();
+ if (!support_can_chroot ())
+ return EXIT_UNSUPPORTED;
+
+ chroot_dir = support_create_temp_directory ("tst-getcwd-abspath-");
+ support_isolate_in_subprocess (getcwd_callback, NULL);
+
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/unix/sysv/linux/getcwd.c b/sysdeps/unix/sysv/linux/getcwd.c
index 3b556fd..f485de8 100644
--- a/sysdeps/unix/sysv/linux/getcwd.c
+++ b/sysdeps/unix/sysv/linux/getcwd.c
@@ -76,7 +76,7 @@ __getcwd (char *buf, size_t size)
int retval;
retval = INLINE_SYSCALL (getcwd, 2, path, alloc_size);
- if (retval >= 0)
+ if (retval > 0 && path[0] == '/')
{
#ifndef NO_ALLOCATION
if (buf == NULL && size == 0)
@@ -92,10 +92,10 @@ __getcwd (char *buf, size_t size)
return buf;
}
- /* The system call cannot handle paths longer than a page.
- Neither can the magic symlink in /proc/self. Just use the
+ /* The system call either cannot handle paths longer than a page
+ or can succeed without returning an absolute path. Just use the
generic implementation right away. */
- if (errno == ENAMETOOLONG)
+ if (retval >= 0 || errno == ENAMETOOLONG)
{
#ifndef NO_ALLOCATION
if (buf == NULL && size == 0)
--
ldv
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2018-01-12 22:24 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-01-01 0:00 [2.26 COMMITTED] linux: make getcwd(3) fail if it cannot obtain an absolute path [BZ #22679] Dmitry V. Levin
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).