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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 <sys/wait.h>
#include "canonicalize.h"
#include "pathnames.h"
#include "all-io.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 *prefix, const char *ptname)
{
FILE *f;
size_t sz;
char path[256], name[sizeof(path) - sizeof(_PATH_DEV_MAPPER)], *res = NULL;
if (!ptname || !*ptname)
return NULL;
if (!prefix)
prefix = "";
snprintf(path, sizeof(path), "%s/sys/block/%s/dm/name", prefix, ptname);
if (!(f = fopen(path, "r" UL_CLOEXECSTR)))
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), _PATH_DEV_MAPPER "/%s", name);
if ((prefix && *prefix) || access(path, F_OK) == 0)
res = strdup(path);
}
fclose(f);
return res;
}
char *canonicalize_dm_name(const char *ptname)
{
return __canonicalize_dm_name(NULL, ptname);
}
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;
}
/*
* This function does not canonicalize the path! It just prepends CWD before a
* relative path. If the path is no relative than returns NULL. The path does
* not have to exist.
*/
char *absolute_path(const char *path)
{
char cwd[PATH_MAX], *res, *p;
size_t psz, csz;
if (!is_relative_path(path)) {
errno = EINVAL;
return NULL;
}
if (!getcwd(cwd, sizeof(cwd)))
return NULL;
/* simple clean up */
if (startswith(path, "./"))
path += 2;
else if (strcmp(path, ".") == 0)
path = NULL;
if (!path || !*path)
return strdup(cwd);
csz = strlen(cwd);
psz = strlen(path);
p = res = malloc(csz + 1 + psz + 1);
if (!res)
return NULL;
memcpy(p, cwd, csz);
p += csz;
*p++ = '/';
memcpy(p, path, psz + 1);
return res;
}
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 = NULL;
int errsv = 0;
int pipes[2];
ssize_t len;
pid_t pid;
if (!path || !*path)
return NULL;
if (pipe(pipes) != 0)
return NULL;
/*
* To accurately assume identity of getuid() we must use setuid()
* but if we do that, we lose ability to reassume euid of 0, so
* we fork to do the check to keep euid intact.
*/
pid = fork();
switch (pid) {
case -1:
close(pipes[0]);
close(pipes[1]);
return NULL; /* fork error */
case 0:
close(pipes[0]); /* close unused end */
pipes[0] = -1;
errno = 0;
/* drop permissions */
if (setgid(getgid()) < 0 || setuid(getuid()) < 0)
canonical = NULL; /* failed */
else {
char *dmname = NULL;
canonical = realpath(path, NULL);
if (canonical && is_dm_devname(canonical, &dmname)) {
char *dm = canonicalize_dm_name(dmname);
if (dm) {
free(canonical);
canonical = dm;
}
}
}
len = canonical ? (ssize_t) strlen(canonical) :
errno ? -errno : -EINVAL;
/* send length or errno */
write_all(pipes[1], (char *) &len, sizeof(len));
if (canonical)
write_all(pipes[1], canonical, len);
exit(0);
default:
break;
}
close(pipes[1]); /* close unused end */
pipes[1] = -1;
/* read size or -errno */
if (read_all(pipes[0], (char *) &len, sizeof(len)) != sizeof(len))
goto done;
if (len < 0) {
errsv = -len;
goto done;
}
canonical = malloc(len + 1);
if (!canonical) {
errsv = ENOMEM;
goto done;
}
/* read path */
if (read_all(pipes[0], canonical, len) != len) {
errsv = errno;
goto done;
}
canonical[len] = '\0';
done:
if (errsv) {
free(canonical);
canonical = NULL;
}
close(pipes[0]);
/* We make a best effort to reap child */
waitpid(pid, NULL, 0);
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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