nvme: code command_id with a genctr for use-after-free validation

We cannot detect a (perhaps buggy) controller that is sending us
a completion for a request that was already completed (for example
sending a completion twice), this phenomenon was seen in the wild
a few times.

So to protect against this, we use the upper 4 msbits of the nvme sqe
command_id to use as a 4-bit generation counter and verify it matches
the existing request generation that is incrementing on every execution.

The 16-bit command_id structure now is constructed by:
| xxxx | xxxxxxxxxxxx |
  gen    request tag

This means that we are giving up some possible queue depth as 12 bits
allow for a maximum queue depth of 4095 instead of 65536, however we
never create such long queues anyways so no real harm done.

Suggested-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Acked-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Daniel Wagner <dwagner@suse.de>
Tested-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/nvme/target/loop.c b/drivers/nvme/target/loop.c
index 3a17a7e26bbf..0285ccc7541f 100644
--- a/drivers/nvme/target/loop.c
+++ b/drivers/nvme/target/loop.c
@@ -107,10 +107,10 @@ static void nvme_loop_queue_response(struct nvmet_req *req)
 	} else {
 		struct request *rq;
 
-		rq = blk_mq_tag_to_rq(nvme_loop_tagset(queue), cqe->command_id);
+		rq = nvme_find_rq(nvme_loop_tagset(queue), cqe->command_id);
 		if (!rq) {
 			dev_err(queue->ctrl->ctrl.device,
-				"tag 0x%x on queue %d not found\n",
+				"got bad command_id %#x on queue %d\n",
 				cqe->command_id, nvme_loop_queue_idx(queue));
 			return;
 		}