glibc/io/tst-lchmod.c
Florian Weimer a492b1e5ef Linux: Work around kernel bugs in chmod on /proc/self/fd paths [BZ #14578]
It appears that the ability to change symbolic link modes through such
paths is unintended.  On several file systems, the operation fails with
EOPNOTSUPP, even though the symbolic link permissions are updated.
The expected behavior is a failure to update the permissions, without
file system changes.

Reviewed-by: Matheus Castanho <msc@linux.ibm.com>
2020-02-18 17:52:27 +01:00

277 lines
8.5 KiB
C

/* Tests for lchmod and fchmodat with AT_SYMLINK_NOFOLLOW.
Copyright (C) 2020 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 <array_length.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <support/check.h>
#include <support/descriptors.h>
#include <support/namespace.h>
#include <support/support.h>
#include <support/temp_file.h>
#include <support/xunistd.h>
#include <unistd.h>
#if __has_include (<sys/mount.h>)
# include <sys/mount.h>
#endif
/* Array of file descriptors. */
#define DYNARRAY_STRUCT fd_list
#define DYNARRAY_ELEMENT int
#define DYNARRAY_INITIAL_SIZE 0
#define DYNARRAY_PREFIX fd_list_
#include <malloc/dynarray-skeleton.c>
static int
fchmodat_with_lchmod (int fd, const char *path, mode_t mode, int flags)
{
TEST_COMPARE (fd, AT_FDCWD);
if (flags == 0)
return chmod (path, mode);
else
{
TEST_COMPARE (flags, AT_SYMLINK_NOFOLLOW);
return lchmod (path, mode);
}
}
/* Chose the appropriate path to pass as the path argument to the *at
functions. */
static const char *
select_path (bool do_relative_path, const char *full_path, const char *relative_path)
{
if (do_relative_path)
return relative_path;
else
return full_path;
}
static void
test_1 (bool do_relative_path, int (*chmod_func) (int fd, const char *, mode_t, int))
{
char *tempdir = support_create_temp_directory ("tst-lchmod-");
char *path_dangling = xasprintf ("%s/dangling", tempdir);
char *path_file = xasprintf ("%s/file", tempdir);
char *path_loop = xasprintf ("%s/loop", tempdir);
char *path_missing = xasprintf ("%s/missing", tempdir);
char *path_to_file = xasprintf ("%s/to-file", tempdir);
int fd;
if (do_relative_path)
fd = xopen (tempdir, O_DIRECTORY | O_RDONLY, 0);
else
fd = AT_FDCWD;
add_temp_file (path_dangling);
add_temp_file (path_loop);
add_temp_file (path_file);
add_temp_file (path_to_file);
support_write_file_string (path_file, "");
xsymlink ("file", path_to_file);
xsymlink ("loop", path_loop);
xsymlink ("target-does-not-exist", path_dangling);
/* Check that the modes do not collide with what we will use in the
test. */
struct stat64 st;
xstat (path_file, &st);
TEST_VERIFY ((st.st_mode & 0777) != 1);
xlstat (path_to_file, &st);
TEST_VERIFY ((st.st_mode & 0777) != 2);
mode_t original_symlink_mode = st.st_mode;
/* We should be able to change the mode of a file, including through
the symbolic link to-file. */
const char *arg = select_path (do_relative_path, path_file, "file");
TEST_COMPARE (chmod_func (fd, arg, 1, 0), 0);
xstat (path_file, &st);
TEST_COMPARE (st.st_mode & 0777, 1);
arg = select_path (do_relative_path, path_to_file, "to-file");
TEST_COMPARE (chmod_func (fd, arg, 2, 0), 0);
xstat (path_file, &st);
TEST_COMPARE (st.st_mode & 0777, 2);
xlstat (path_to_file, &st);
TEST_COMPARE (original_symlink_mode, st.st_mode);
arg = select_path (do_relative_path, path_file, "file");
TEST_COMPARE (chmod_func (fd, arg, 1, 0), 0);
xstat (path_file, &st);
TEST_COMPARE (st.st_mode & 0777, 1);
xlstat (path_to_file, &st);
TEST_COMPARE (original_symlink_mode, st.st_mode);
/* Changing the mode of a symbolic link should fail. */
arg = select_path (do_relative_path, path_to_file, "to-file");
int ret = chmod_func (fd, arg, 2, AT_SYMLINK_NOFOLLOW);
TEST_COMPARE (ret, -1);
TEST_COMPARE (errno, EOPNOTSUPP);
/* The modes should remain unchanged. */
xstat (path_file, &st);
TEST_COMPARE (st.st_mode & 0777, 1);
xlstat (path_to_file, &st);
TEST_COMPARE (original_symlink_mode, st.st_mode);
/* Likewise, changing dangling and looping symbolic links must
fail. */
const char *paths[] = { path_dangling, path_loop };
for (size_t i = 0; i < array_length (paths); ++i)
{
const char *path = paths[i];
const char *filename = strrchr (path, '/');
TEST_VERIFY_EXIT (filename != NULL);
++filename;
mode_t new_mode = 010 + i;
xlstat (path, &st);
TEST_VERIFY ((st.st_mode & 0777) != new_mode);
original_symlink_mode = st.st_mode;
arg = select_path (do_relative_path, path, filename);
ret = chmod_func (fd, arg, new_mode, AT_SYMLINK_NOFOLLOW);
TEST_COMPARE (ret, -1);
TEST_COMPARE (errno, EOPNOTSUPP);
xlstat (path, &st);
TEST_COMPARE (st.st_mode, original_symlink_mode);
}
/* A missing file should always result in ENOENT. The presence of
/proc does not matter. */
arg = select_path (do_relative_path, path_missing, "missing");
TEST_COMPARE (chmod_func (fd, arg, 020, 0), -1);
TEST_COMPARE (errno, ENOENT);
TEST_COMPARE (chmod_func (fd, arg, 020, AT_SYMLINK_NOFOLLOW), -1);
TEST_COMPARE (errno, ENOENT);
/* Test without available file descriptors. */
{
struct fd_list fd_list;
fd_list_init (&fd_list);
while (true)
{
int ret = dup (STDOUT_FILENO);
if (ret == -1)
{
if (errno == ENFILE || errno == EMFILE)
break;
FAIL_EXIT1 ("dup: %m");
}
fd_list_add (&fd_list, ret);
TEST_VERIFY_EXIT (!fd_list_has_failed (&fd_list));
}
/* Without AT_SYMLINK_NOFOLLOW, changing the permissions should
work as before. */
arg = select_path (do_relative_path, path_file, "file");
TEST_COMPARE (chmod_func (fd, arg, 3, 0), 0);
xstat (path_file, &st);
TEST_COMPARE (st.st_mode & 0777, 3);
/* But with AT_SYMLINK_NOFOLLOW, even if we originally had
support, we may have lost it. */
ret = chmod_func (fd, arg, 2, AT_SYMLINK_NOFOLLOW);
if (ret == 0)
{
xstat (path_file, &st);
TEST_COMPARE (st.st_mode & 0777, 2);
}
else
{
TEST_COMPARE (ret, -1);
/* The error code from the openat fallback leaks out. */
if (errno != ENFILE && errno != EMFILE)
TEST_COMPARE (errno, EOPNOTSUPP);
}
xstat (path_file, &st);
TEST_COMPARE (st.st_mode & 0777, 3);
/* Close the descriptors. */
for (int *pfd = fd_list_begin (&fd_list); pfd < fd_list_end (&fd_list);
++pfd)
xclose (*pfd);
fd_list_free (&fd_list);
}
if (do_relative_path)
xclose (fd);
free (path_dangling);
free (path_file);
free (path_loop);
free (path_missing);
free (path_to_file);
free (tempdir);
}
static void
test_3 (void)
{
puts ("info: testing lchmod");
test_1 (false, fchmodat_with_lchmod);
puts ("info: testing fchmodat with AT_FDCWD");
test_1 (false, fchmodat);
puts ("info: testing fchmodat with relative path");
test_1 (true, fchmodat);
}
static int
do_test (void)
{
struct support_descriptors *descriptors = support_descriptors_list ();
/* Run the three tests in the default environment. */
test_3 ();
/* Try to set up a /proc-less environment and re-test. */
#if __has_include (<sys/mount.h>)
if (!support_become_root ())
puts ("warning: could not obtain root-like privileges");
if (!support_enter_mount_namespace ())
puts ("warning: could enter a mount namespace");
else
{
/* Attempt to mount an empty directory over /proc. */
char *tempdir = support_create_temp_directory ("tst-lchmod-");
bool proc_emptied
= mount (tempdir, "/proc", "none", MS_BIND, NULL) == 0;
if (!proc_emptied)
printf ("warning: bind-mounting /proc failed: %m");
free (tempdir);
puts ("info: re-running tests (after trying to empty /proc)");
test_3 ();
if (proc_emptied)
/* Reveal the original /proc, which is needed by the
descriptors check below. */
TEST_COMPARE (umount ("/proc"), 0);
}
#endif /* <sys/mount.h>. */
support_descriptors_check (descriptors);
support_descriptors_free (descriptors);
return 0;
}
#include <support/test-driver.c>