kpartx: fix segfault when operating on regular files

The following problem has been introduced in multipath-tools 0.14.0:

> truncate -s1G /tmp/img
> kpartx -a /tmp/img
double free or corruption (out)
Aborted                    (core dumped) kpartx -a /tmp/img

Fix it by always allocating "uuid" on the heap, rather than
using a static char array.

Fixes: 8c39e60 ("kpartx: fix some memory leaks")
Fixes: #139
Signed-off-by: Martin Wilck <mwilck@suse.com>
Reviewed-by: Benjamin Marzinski <bmarzins@redhat.com>

Author: mwilck

kpartx/devmapper.c

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2004, 2005 Christophe Varoqui
  */
+#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -699,14 +700,13 @@ int dm_find_part(const char *parent, const char *delim, int part,
 
 char *nondm_create_uuid(dev_t devt)
 {
-#define NONDM_UUID_BUFLEN (34 + sizeof(NONDM_UUID_PREFIX) + \
-			   sizeof(NONDM_UUID_SUFFIX))
-	static char uuid_buf[NONDM_UUID_BUFLEN];
-	snprintf(uuid_buf, sizeof(uuid_buf), "%s_%u:%u_%s",
-		 NONDM_UUID_PREFIX, major(devt), minor(devt),
-		 NONDM_UUID_SUFFIX);
-	uuid_buf[NONDM_UUID_BUFLEN-1] = '\0';
-	return uuid_buf;
+	char *uuid;
+
+	if (asprintf(&uuid, "%s_%u:%u_%s", NONDM_UUID_PREFIX, major(devt),
+		     minor(devt), NONDM_UUID_SUFFIX) >= 0)
+		return uuid;
+	else
+		return NULL;
 }
 
 int nondm_parse_uuid(const char *uuid, unsigned int *major, unsigned int *minor)

kpartx/kpartx.c

@@ -404,8 +404,11 @@ main(int argc, char **argv){
 	 * This allows deletion of partitions created with older kpartx
 	 * versions which didn't use the fake UUID during creation.
 	 */
-	if (!uuid && !(what == DELETE && force_devmap))
+	if (!uuid && !(what == DELETE && force_devmap)) {
 		uuid = nondm_create_uuid(buf.st_rdev);
+		if (!uuid)
+			exit(1);
+	}
 
 	if (delim == NULL) {
 		delim = xmalloc(DELIM_SIZE);