um: Fix initialization of vector queues

UML vector drivers could derefence uninitialized memory
when cleaning up after a queue allocation failure.

Fixes: 49da7e64f3 ("High Performance UML Vector Network Driver")
Cc: <stable@vger.kernel.org>
Reported-by: Dan Capenter <dan.carpenter@oracle.com>
Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/drivers/vector_kern.c

@@ -504,15 +504,19 @@ static struct vector_queue *create_queue(
 
 	result = kmalloc(sizeof(struct vector_queue), GFP_KERNEL);
 	if (result == NULL)
-		goto out_fail;
+		return NULL;
 	result->max_depth = max_size;
 	result->dev = vp->dev;
 	result->mmsg_vector = kmalloc(
 		(sizeof(struct mmsghdr) * max_size), GFP_KERNEL);
+	if (result->mmsg_vector == NULL)
+		goto out_mmsg_fail;
 	result->skbuff_vector = kmalloc(
 		(sizeof(void *) * max_size), GFP_KERNEL);
-	if (result->mmsg_vector == NULL || result->skbuff_vector == NULL)
-		goto out_fail;
+	if (result->skbuff_vector == NULL)
+		goto out_skb_fail;
+
+	/* further failures can be handled safely by destroy_queue*/
 
 	mmsg_vector = result->mmsg_vector;
 	for (i = 0; i < max_size; i++) {
@@ -563,6 +567,11 @@ static struct vector_queue *create_queue(
 	result->head = 0;
 	result->tail = 0;
 	return result;
+out_skb_fail:
+	kfree(result->mmsg_vector);
+out_mmsg_fail:
+	kfree(result);
+	return NULL;
 out_fail:
 	destroy_queue(result);
 	return NULL;