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/* like chdir(2), but safer, if possible
Copyright (C) 2005 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 2, 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, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
/* written by Jim Meyering */
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include "chdir-safer.h"
#include <stdbool.h>
#include <stdio.h>
#include <assert.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "fcntl--.h" /* for the open->open_safer mapping */
#if !defined O_NOFOLLOW
# define O_NOFOLLOW 0
#endif
#define SAME_INODE(Stat_buf_1, Stat_buf_2) \
((Stat_buf_1).st_ino == (Stat_buf_2).st_ino \
&& (Stat_buf_1).st_dev == (Stat_buf_2).st_dev)
/* Just like chmod, but fail if DIR is a symbolic link.
This can avoid a minor race condition between when a
directory is created or stat'd and when we chdir into it. */
int
chdir_no_follow (char const *dir)
{
int fail = -1;
struct stat sb;
struct stat sb_init;
int saved_errno = 0;
int fd;
bool open_dereferences_symlink = ! O_NOFOLLOW;
/* If open follows symlinks, lstat DIR first to ensure that it is
a directory and to get its device and inode numbers. */
if (open_dereferences_symlink
&& (lstat (dir, &sb_init) != 0 || ! S_ISDIR (sb_init.st_mode)))
return fail;
fd = open (dir, O_NOFOLLOW | O_RDONLY | O_NDELAY);
if (0 <= fd
&& fstat (fd, &sb) == 0
/* If DIR is a different directory, then someone is trying to do
something nasty. However, the risk of
such an attack is so low that it isn't worth a special diagnostic.
Simply skip the fchdir and set errno (to the same value that open
uses for symlinks with O_NOFOLLOW), so that the caller can
report the failure. */
&& ( ! open_dereferences_symlink || SAME_INODE (sb_init, sb)
|| ((errno = ELOOP), 0))
&& fchdir (fd) == 0)
{
fail = 0;
}
else
{
saved_errno = errno;
}
if (0 < fd)
close (fd); /* Ignore any failure. */
errno = saved_errno;
return fail;
}
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