RDMA/rxe: Fix coding error in rxe_rcv_mcast_pkt

rxe_rcv_mcast_pkt() in rxe_recv.c can leak SKBs in error path code. The
loop over the QPs attached to a multicast group creates new cloned SKBs
for all but the last QP in the list and passes the SKB and its clones to
rxe_rcv_pkt() for further processing. Any QPs that do not pass some checks
are skipped.  If the last QP in the list fails the tests the SKB is
leaked.  This patch checks if the SKB for the last QP was used and if not
frees it. Also removes a redundant loop invariant assignment.

Fixes: 8700e3e ("Soft RoCE driver")
Fixes: 71abf20 ("RDMA/rxe: Handle skb_clone() failure in rxe_recv.c")
Link: https://lore.kernel.org/r/20210128174752.16128-1-rpearson@hpe.com
Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/sw/rxe/rxe_recv.c

@@ -256,7 +256,6 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
 
 	list_for_each_entry(mce, &mcg->qp_list, qp_list) {
 		qp = mce->qp;
-		pkt = SKB_TO_PKT(skb);
 
 		/* validate qp for incoming packet */
 		err = check_type_state(rxe, pkt, qp);
@@ -268,12 +267,18 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
 			continue;
 
 		/* for all but the last qp create a new clone of the
-		 * skb and pass to the qp.
+		 * skb and pass to the qp. If an error occurs in the
+		 * checks for the last qp in the list we need to
+		 * free the skb since it hasn't been passed on to
+		 * rxe_rcv_pkt() which would free it later.
 		 */
-		if (mce->qp_list.next != &mcg->qp_list)
+		if (mce->qp_list.next != &mcg->qp_list) {
 			per_qp_skb = skb_clone(skb, GFP_ATOMIC);
-		else
+		} else {
 			per_qp_skb = skb;
+			/* show we have consumed the skb */
+			skb = NULL;
+		}
 
 		if (unlikely(!per_qp_skb))
 			continue;
@@ -288,9 +293,8 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
 
 	rxe_drop_ref(mcg);	/* drop ref from rxe_pool_get_key. */
 
-	return;
-
 err1:
+	/* free skb if not consumed */
 	kfree_skb(skb);
 }