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/*
* chroot_realpath.c -- reslove pathname as if inside chroot
* Based on realpath.c Copyright (C) 1993 Rick Sladkey <jrs@world.std.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Library 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 Library Public License for more details.
*
* 2005/09/12: Dan Howell (modified from realpath.c to emulate chroot)
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <limits.h> /* for PATH_MAX */
#include <sys/param.h> /* for MAXPATHLEN */
#include <errno.h>
#ifndef __set_errno
#define __set_errno(val) ((errno) = (val))
#endif
#include <sys/stat.h> /* for S_IFLNK */
#ifndef PATH_MAX
#define PATH_MAX _POSIX_PATH_MAX
#endif
#define MAX_READLINKS 32
char *chroot_realpath(const char *chroot, const char *path, char resolved_path[])
{
char copy_path[PATH_MAX];
char link_path[PATH_MAX];
char got_path[PATH_MAX];
char *got_path_root = got_path;
char *new_path = got_path;
char *max_path;
int readlinks = 0;
int n;
int chroot_len;
/* Trivial case. */
if (chroot == NULL || *chroot == '\0' ||
(*chroot == '/' && chroot[1] == '\0')) {
strcpy(resolved_path, path);
return resolved_path;
}
chroot_len = strlen(chroot);
if (chroot_len + strlen(path) >= PATH_MAX - 3) {
__set_errno(ENAMETOOLONG);
return NULL;
}
/* Make a copy of the source path since we may need to modify it. */
strcpy(copy_path, path);
path = copy_path;
max_path = copy_path + PATH_MAX - chroot_len - 3;
/* Start with the chroot path. */
strcpy(new_path, chroot);
new_path += chroot_len;
while (*new_path == '/' && new_path > got_path)
new_path--;
got_path_root = new_path;
*new_path++ = '/';
/* Expand each slash-separated pathname component. */
while (*path != '\0') {
/* Ignore stray "/". */
if (*path == '/') {
path++;
continue;
}
if (*path == '.') {
/* Ignore ".". */
if (path[1] == '\0' || path[1] == '/') {
path++;
continue;
}
if (path[1] == '.') {
if (path[2] == '\0' || path[2] == '/') {
path += 2;
/* Ignore ".." at root. */
if (new_path == got_path_root + 1)
continue;
/* Handle ".." by backing up. */
while ((--new_path)[-1] != '/');
continue;
}
}
}
/* Safely copy the next pathname component. */
while (*path != '\0' && *path != '/') {
if (path > max_path) {
__set_errno(ENAMETOOLONG);
return NULL;
}
*new_path++ = *path++;
}
if (*path == '\0')
/* Don't follow symlink for last pathname component. */
break;
#ifdef S_IFLNK
/* Protect against infinite loops. */
if (readlinks++ > MAX_READLINKS) {
__set_errno(ELOOP);
return NULL;
}
/* See if latest pathname component is a symlink. */
*new_path = '\0';
n = readlink(got_path, link_path, PATH_MAX - 1);
if (n < 0) {
/* EINVAL means the file exists but isn't a symlink. */
if (errno != EINVAL) {
/* Make sure it's null terminated. */
*new_path = '\0';
strcpy(resolved_path, got_path);
return NULL;
}
} else {
/* Note: readlink doesn't add the null byte. */
link_path[n] = '\0';
if (*link_path == '/')
/* Start over for an absolute symlink. */
new_path = got_path_root;
else
/* Otherwise back up over this component. */
while (*(--new_path) != '/');
/* Safe sex check. */
if (strlen(path) + n >= PATH_MAX - 2) {
__set_errno(ENAMETOOLONG);
return NULL;
}
/* Insert symlink contents into path. */
strcat(link_path, path);
strcpy(copy_path, link_path);
path = copy_path;
}
#endif /* S_IFLNK */
*new_path++ = '/';
}
/* Delete trailing slash but don't whomp a lone slash. */
if (new_path != got_path + 1 && new_path[-1] == '/')
new_path--;
/* Make sure it's null terminated. */
*new_path = '\0';
strcpy(resolved_path, got_path);
return resolved_path;
}
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