eCryptfs: use after free in ecryptfs_release_messaging()

BugLink: http://bugs.launchpad.net/bugs/1744873

commit db86be3a upstream.

We're freeing the list iterator so we should be using the _safe()
version of hlist_for_each_entry().

Fixes: 88b4a07e ("[PATCH] eCryptfs: Public key transport mechanism")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

fs/ecryptfs/messaging.c

@@ -442,15 +442,16 @@ void ecryptfs_release_messaging(void)
 	}
 	if (ecryptfs_daemon_hash) {
 		struct ecryptfs_daemon *daemon;
+		struct hlist_node *n;
 		int i;
 
 		mutex_lock(&ecryptfs_daemon_hash_mux);
 		for (i = 0; i < (1 << ecryptfs_hash_bits); i++) {
 			int rc;
 
-			hlist_for_each_entry(daemon,
-					     &ecryptfs_daemon_hash[i],
-					     euid_chain) {
+			hlist_for_each_entry_safe(daemon, n,
+						  &ecryptfs_daemon_hash[i],
+						  euid_chain) {
 				rc = ecryptfs_exorcise_daemon(daemon);
 				if (rc)
 					printk(KERN_ERR "%s: Error whilst "