RDMA/rxe: Fix unsafe drain work queue code

If create_qp does not fully succeed it is possible for qp cleanup
code to attempt to drain the send or recv work queues before the
queues have been created causing a seg fault. This patch checks
to see if the queues exist before attempting to drain them.

Link: https://lore.kernel.org/r/20230620135519.9365-3-rpearsonhpe@gmail.com
Reported-by: syzbot+2da1965168e7dbcba136@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-rdma/00000000000012d89205fe7cfe00@google.com/raw
Fixes: 49dc9c1f0c ("RDMA/rxe: Cleanup reset state handling in rxe_resp.c")
Fixes: fbdeb828a2 ("RDMA/rxe: Cleanup error state handling in rxe_comp.c")
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/sw/rxe/rxe_comp.c

@@ -597,6 +597,10 @@ static void flush_send_queue(struct rxe_qp *qp, bool notify)
 	struct rxe_queue *q = qp->sq.queue;
 	int err;
 
+	/* send queue never got created. nothing to do. */
+	if (!qp->sq.queue)
+		return;
+
 	while ((wqe = queue_head(q, q->type))) {
 		if (notify) {
 			err = flush_send_wqe(qp, wqe);

drivers/infiniband/sw/rxe/rxe_resp.c

@@ -1469,6 +1469,10 @@ static void flush_recv_queue(struct rxe_qp *qp, bool notify)
 		return;
 	}
 
+	/* recv queue not created. nothing to do. */
+	if (!qp->rq.queue)
+		return;
+
 	while ((wqe = queue_head(q, q->type))) {
 		if (notify) {
 			err = flush_recv_wqe(qp, wqe);