RDMA/rxe: Fix bug rejecting all multicast packets

Fix a bug in rxe_rcv() that causes all multicast packets to be
dropped. Currently rxe_match_dgid() is called for each packet to verify
that the destination IP address matches one of the entries in the port
source GID table. This is incorrect for IP multicast addresses since they
do not appear in the GID table.

Add code to detect multicast addresses.

Change function name to rxe_chk_dgid() which is clearer.

Link: https://lore.kernel.org/r/20201008212753.265249-1-rpearson@hpe.com
Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: rpearsonhpe-design

drivers/infiniband/sw/rxe/rxe_recv.c

@@ -287,7 +287,17 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
 	kfree_skb(skb);
 }
 
-static int rxe_match_dgid(struct rxe_dev *rxe, struct sk_buff *skb)
+/**
+ * rxe_chk_dgid - validate destination IP address
+ * @rxe: rxe device that received packet
+ * @skb: the received packet buffer
+ *
+ * Accept any loopback packets
+ * Extract IP address from packet and
+ * Accept if multicast packet
+ * Accept if matches an SGID table entry
+ */
+static int rxe_chk_dgid(struct rxe_dev *rxe, struct sk_buff *skb)
 {
 	struct rxe_pkt_info *pkt = SKB_TO_PKT(skb);
 	const struct ib_gid_attr *gid_attr;
@@ -305,6 +315,9 @@ static int rxe_match_dgid(struct rxe_dev *rxe, struct sk_buff *skb)
 		pdgid = (union ib_gid *)&ipv6_hdr(skb)->daddr;
 	}
 
+	if (rdma_is_multicast_addr((struct in6_addr *)pdgid))
+		return 0;
+
 	gid_attr = rdma_find_gid_by_port(&rxe->ib_dev, pdgid,
 					 IB_GID_TYPE_ROCE_UDP_ENCAP,
 					 1, skb->dev);
@@ -329,8 +342,8 @@ void rxe_rcv(struct sk_buff *skb)
 	if (unlikely(skb->len < pkt->offset + RXE_BTH_BYTES))
 		goto drop;
 
-	if (rxe_match_dgid(rxe, skb) < 0) {
-		pr_warn_ratelimited("failed matching dgid\n");
+	if (rxe_chk_dgid(rxe, skb) < 0) {
+		pr_warn_ratelimited("failed checking dgid\n");
 		goto drop;
 	}