nvmet-rdma: fix possible bad dereference when freeing rsps

It is possible that the host connected and saw a cm established
event and started sending nvme capsules on the qp, however the
ctrl did not yet see an established event. This is why the
rsp_wait_list exists (for async handling of these cmds, we move
them to a pending list).

Furthermore, it is possible that the ctrl cm times out, resulting
in a connect-error cm event. in this case we hit a bad deref [1]
because in nvmet_rdma_free_rsps we assume that all the responses
are in the free list.

We are freeing the cmds array anyways, so don't even bother to
remove the rsp from the free_list. It is also guaranteed that we
are not racing anything when we are releasing the queue so no
other context accessing this array should be running.

[1]:
--
Workqueue: nvmet-free-wq nvmet_rdma_free_queue_work [nvmet_rdma]
[...]
pc : nvmet_rdma_free_rsps+0x78/0xb8 [nvmet_rdma]
lr : nvmet_rdma_free_queue_work+0x88/0x120 [nvmet_rdma]
 Call trace:
 nvmet_rdma_free_rsps+0x78/0xb8 [nvmet_rdma]
 nvmet_rdma_free_queue_work+0x88/0x120 [nvmet_rdma]
 process_one_work+0x1ec/0x4a0
 worker_thread+0x48/0x490
 kthread+0x158/0x160
 ret_from_fork+0x10/0x18
--

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>

Author: sagigrimberg

drivers/nvme/target/rdma.c

@@ -474,12 +474,8 @@ nvmet_rdma_alloc_rsps(struct nvmet_rdma_queue *queue)
 	return 0;
 
 out_free:
-	while (--i >= 0) {
-		struct nvmet_rdma_rsp *rsp = &queue->rsps[i];
-
-		list_del(&rsp->free_list);
-		nvmet_rdma_free_rsp(ndev, rsp);
-	}
+	while (--i >= 0)
+		nvmet_rdma_free_rsp(ndev, &queue->rsps[i]);
 	kfree(queue->rsps);
 out:
 	return ret;
@@ -490,12 +486,8 @@ static void nvmet_rdma_free_rsps(struct nvmet_rdma_queue *queue)
 	struct nvmet_rdma_device *ndev = queue->dev;
 	int i, nr_rsps = queue->recv_queue_size * 2;
 
-	for (i = 0; i < nr_rsps; i++) {
-		struct nvmet_rdma_rsp *rsp = &queue->rsps[i];
-
-		list_del(&rsp->free_list);
-		nvmet_rdma_free_rsp(ndev, rsp);
-	}
+	for (i = 0; i < nr_rsps; i++)
+		nvmet_rdma_free_rsp(ndev, &queue->rsps[i]);
 	kfree(queue->rsps);
 }