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/* much like chdir(2), but safer
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 <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#ifndef O_DIRECTORY
# define O_DIRECTORY 0
#endif
#ifndef 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)
/* Like chdir, but fail if DIR is a symbolic link to a directory (or
similar funny business), or if DIR is neither readable nor
writable. This avoids a minor race condition between when a
directory is created or statted and when the process chdirs into it.
On some systems, a writable yet unreadable directory cannot be
opened via open with O_WRONLY. For example, on Linux 2.6, the
open syscall fails with EISDIR. */
int
chdir_no_follow (char const *dir)
{
int result = 0;
int saved_errno;
int open_flags = O_DIRECTORY | O_NOCTTY | O_NOFOLLOW | O_NONBLOCK;
int fd = open (dir, O_RDONLY | open_flags);
if (fd < 0)
{
if (errno == EACCES)
fd = open (dir, O_WRONLY | open_flags);
if (fd < 0)
return fd;
}
/* 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. */
if (! 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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