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/* much like chdir(2), but safer
Copyright (C) 2005-2006, 2008-2014 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
/* written by Jim Meyering */
#include <config.h>
#include "chdir-safer.h"
#include <stdbool.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "same-inode.h"
#ifndef HAVE_READLINK
# define HAVE_READLINK 0
#endif
/* Like chdir, but fail if DIR is a symbolic link to a directory (or
similar funny business). This avoids a minor race condition
between when a directory is created or statted and when the process
chdirs into it.
On older systems lacking full support for O_SEARCH, this function
can also fail if DIR is not readable. */
int
chdir_no_follow (char const *dir)
{
int result = 0;
int saved_errno;
int fd = open (dir,
O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NOFOLLOW | O_NONBLOCK);
if (fd < 0)
return -1;
/* If open follows symlinks, lstat DIR and fstat FD to ensure that
they are the same file; if they are different files, set errno to
ELOOP (the same value that open uses for symlinks with
O_NOFOLLOW) so the caller can report a failure.
Skip this check if HAVE_READLINK == 0, which should be the case
on any system that lacks symlink support. */
if (HAVE_READLINK && ! HAVE_WORKING_O_NOFOLLOW)
{
struct stat sb1;
result = lstat (dir, &sb1);
if (result == 0)
{
struct stat sb2;
result = fstat (fd, &sb2);
if (result == 0 && ! SAME_INODE (sb1, sb2))
{
errno = ELOOP;
result = -1;
}
}
}
if (result == 0)
result = fchdir (fd);
saved_errno = errno;
close (fd);
errno = saved_errno;
return result;
}
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