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/*
* canonicalize.c -- canonicalize pathname by removing symlinks
*
* This file may be distributed under the terms of the
* GNU Lesser General Public License.
*
* Copyright (C) 2009-2013 Karel Zak <kzak@redhat.com>
*/
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "canonicalize.h"
/*
* Converts private "dm-N" names to "/dev/mapper/<name>"
*
* Since 2.6.29 (patch 784aae735d9b0bba3f8b9faef4c8b30df3bf0128) kernel sysfs
* provides the real DM device names in /sys/block/<ptname>/dm/name
*/
char *canonicalize_dm_name(const char *ptname)
{
FILE *f;
size_t sz;
char path[256], name[256], *res = NULL;
if (!ptname || !*ptname)
return NULL;
snprintf(path, sizeof(path), "/sys/block/%s/dm/name", ptname);
if (!(f = fopen(path, "r")))
return NULL;
/* read "<name>\n" from sysfs */
if (fgets(name, sizeof(name), f) && (sz = strlen(name)) > 1) {
name[sz - 1] = '\0';
snprintf(path, sizeof(path), "/dev/mapper/%s", name);
if (access(path, F_OK) == 0)
res = strdup(path);
}
fclose(f);
return res;
}
static int is_dm_devname(char *canonical, char **name)
{
struct stat sb;
char *p = strrchr(canonical, '/');
*name = NULL;
if (!p
|| strncmp(p, "/dm-", 4) != 0
|| !isdigit(*(p + 4))
|| stat(canonical, &sb) != 0
|| !S_ISBLK(sb.st_mode))
return 0;
*name = p + 1;
return 1;
}
char *canonicalize_path(const char *path)
{
char *canonical, *dmname;
if (!path || !*path)
return NULL;
canonical = realpath(path, NULL);
if (!canonical)
return strdup(path);
if (is_dm_devname(canonical, &dmname)) {
char *dm = canonicalize_dm_name(dmname);
if (dm) {
free(canonical);
return dm;
}
}
return canonical;
}
char *canonicalize_path_restricted(const char *path)
{
char *canonical, *dmname;
int errsv;
uid_t euid;
gid_t egid;
if (!path || !*path)
return NULL;
euid = geteuid();
egid = getegid();
/* drop permissions */
if (setegid(getgid()) < 0 || seteuid(getuid()) < 0)
return NULL;
errsv = errno = 0;
canonical = realpath(path, NULL);
if (!canonical)
errsv = errno;
else if (is_dm_devname(canonical, &dmname)) {
char *dm = canonicalize_dm_name(dmname);
if (dm) {
free(canonical);
canonical = dm;
}
}
/* restore */
if (setegid(egid) < 0 || seteuid(euid) < 0) {
free(canonical);
return NULL;
}
errno = errsv;
return canonical;
}
#ifdef TEST_PROGRAM_CANONICALIZE
int main(int argc, char **argv)
{
if (argc < 2) {
fprintf(stderr, "usage: %s <device>\n", argv[0]);
exit(EXIT_FAILURE);
}
fprintf(stdout, "orig: %s\n", argv[1]);
fprintf(stdout, "real: %s\n", canonicalize_path(argv[1]));
exit(EXIT_SUCCESS);
}
#endif
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