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glibc/elf/chroot_canon.c
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/* Return the canonical absolute name of a given file inside chroot. | |
Copyright (C) 1996-2016 Free Software Foundation, Inc. | |
This file is part of the GNU C Library. | |
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; version 2 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/>. */ | |
#include <stdlib.h> | |
#include <string.h> | |
#include <unistd.h> | |
#include <limits.h> | |
#include <sys/stat.h> | |
#include <errno.h> | |
#include <stddef.h> | |
#include <stdint.h> | |
#include <eloop-threshold.h> | |
#include <ldconfig.h> | |
#ifndef PATH_MAX | |
#define PATH_MAX 1024 | |
#endif | |
/* Return the canonical absolute name of file NAME as if chroot(CHROOT) was | |
done first. A canonical name does not contain any `.', `..' components | |
nor any repeated path separators ('/') or symlinks. All path components | |
must exist and NAME must be absolute filename. The result is malloc'd. | |
The returned name includes the CHROOT prefix. */ | |
char * | |
chroot_canon (const char *chroot, const char *name) | |
{ | |
char *rpath; | |
char *dest; | |
char *extra_buf = NULL; | |
char *rpath_root; | |
const char *start; | |
const char *end; | |
const char *rpath_limit; | |
int num_links = 0; | |
size_t chroot_len = strlen (chroot); | |
if (chroot_len < 1) | |
{ | |
__set_errno (EINVAL); | |
return NULL; | |
} | |
rpath = xmalloc (chroot_len + PATH_MAX); | |
rpath_limit = rpath + chroot_len + PATH_MAX; | |
rpath_root = (char *) mempcpy (rpath, chroot, chroot_len) - 1; | |
if (*rpath_root != '/') | |
*++rpath_root = '/'; | |
dest = rpath_root + 1; | |
for (start = end = name; *start; start = end) | |
{ | |
struct stat64 st; | |
/* Skip sequence of multiple path-separators. */ | |
while (*start == '/') | |
++start; | |
/* Find end of path component. */ | |
for (end = start; *end && *end != '/'; ++end) | |
/* Nothing. */; | |
if (end - start == 0) | |
break; | |
else if (end - start == 1 && start[0] == '.') | |
/* nothing */; | |
else if (end - start == 2 && start[0] == '.' && start[1] == '.') | |
{ | |
/* Back up to previous component, ignore if at root already. */ | |
if (dest > rpath_root + 1) | |
while ((--dest)[-1] != '/'); | |
} | |
else | |
{ | |
size_t new_size; | |
if (dest[-1] != '/') | |
*dest++ = '/'; | |
if (dest + (end - start) >= rpath_limit) | |
{ | |
ptrdiff_t dest_offset = dest - rpath; | |
char *new_rpath; | |
new_size = rpath_limit - rpath; | |
if (end - start + 1 > PATH_MAX) | |
new_size += end - start + 1; | |
else | |
new_size += PATH_MAX; | |
new_rpath = (char *) xrealloc (rpath, new_size); | |
rpath = new_rpath; | |
rpath_limit = rpath + new_size; | |
dest = rpath + dest_offset; | |
} | |
dest = mempcpy (dest, start, end - start); | |
*dest = '\0'; | |
if (lstat64 (rpath, &st) < 0) | |
{ | |
if (*end == '\0') | |
goto done; | |
goto error; | |
} | |
if (S_ISLNK (st.st_mode)) | |
{ | |
char *buf = alloca (PATH_MAX); | |
size_t len; | |
if (++num_links > __eloop_threshold ()) | |
{ | |
__set_errno (ELOOP); | |
goto error; | |
} | |
ssize_t n = readlink (rpath, buf, PATH_MAX - 1); | |
if (n < 0) | |
{ | |
if (*end == '\0') | |
goto done; | |
goto error; | |
} | |
buf[n] = '\0'; | |
if (!extra_buf) | |
extra_buf = alloca (PATH_MAX); | |
len = strlen (end); | |
if (len >= PATH_MAX - n) | |
{ | |
__set_errno (ENAMETOOLONG); | |
goto error; | |
} | |
/* Careful here, end may be a pointer into extra_buf... */ | |
memmove (&extra_buf[n], end, len + 1); | |
name = end = memcpy (extra_buf, buf, n); | |
if (buf[0] == '/') | |
dest = rpath_root + 1; /* It's an absolute symlink */ | |
else | |
/* Back up to previous component, ignore if at root already: */ | |
if (dest > rpath_root + 1) | |
while ((--dest)[-1] != '/'); | |
} | |
} | |
} | |
done: | |
if (dest > rpath_root + 1 && dest[-1] == '/') | |
--dest; | |
*dest = '\0'; | |
return rpath; | |
error: | |
free (rpath); | |
return NULL; | |
} |