1 files changed, 145 insertions, 0 deletions
diff --git a/libblkid/lib/canonicalize.c b/libblkid/lib/canonicalize.c
new file mode 100644
index 000000000..303703b7c
--- /dev/null
+++ b/libblkid/lib/canonicalize.c
@@ -0,0 +1,145 @@
+/*
+ * 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