cifs: integer overflow in parse_dacl()

On 32 bit systems num_aces * sizeof(struct cifs_ace *) could overflow
leading to a smaller ppace buffer than we expected.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Jeff Layton <jlayton@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsacl.c

@@ -909,6 +909,8 @@ static void parse_dacl(struct cifs_acl *pdacl, char *end_of_acl,
 		umode_t group_mask = S_IRWXG;
 		umode_t other_mask = S_IRWXU | S_IRWXG | S_IRWXO;
 
+		if (num_aces > ULONG_MAX / sizeof(struct cifs_ace *))
+			return;
 		ppace = kmalloc(num_aces * sizeof(struct cifs_ace *),
 				GFP_KERNEL);
 		if (!ppace) {