net: rds: Fix possible NULL-pointer dereference

In rds_rdma_cm_event_handler_cmn() check, if conn pointer exists
before dereferencing it as rdma_set_service_type() argument

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: fd261ce ("rds: rdma: update rdma transport for tos")
Signed-off-by: Artem Chernyshev <artem.chernyshev@red-soft.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: dTenebrae

net/rds/rdma_transport.c

@@ -86,11 +86,13 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id,
 		break;
 
 	case RDMA_CM_EVENT_ADDR_RESOLVED:
-		rdma_set_service_type(cm_id, conn->c_tos);
-		rdma_set_min_rnr_timer(cm_id, IB_RNR_TIMER_000_32);
-		/* XXX do we need to clean up if this fails? */
-		ret = rdma_resolve_route(cm_id,
-					 RDS_RDMA_RESOLVE_TIMEOUT_MS);
+		if (conn) {
+			rdma_set_service_type(cm_id, conn->c_tos);
+			rdma_set_min_rnr_timer(cm_id, IB_RNR_TIMER_000_32);
+			/* XXX do we need to clean up if this fails? */
+			ret = rdma_resolve_route(cm_id,
+						 RDS_RDMA_RESOLVE_TIMEOUT_MS);
+		}
 		break;
 
 	case RDMA_CM_EVENT_ROUTE_RESOLVED: