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