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>

drivers/nvme/host/core.c

@@ -1026,7 +1026,8 @@ blk_status_t nvme_setup_cmd(struct nvme_ns *ns, struct request *req)
 		return BLK_STS_IOERR;
 	}
 
-	cmd->common.command_id = req->tag;
+	nvme_req(req)->genctr++;
+	cmd->common.command_id = nvme_cid(req);
 	trace_nvme_setup_cmd(req, cmd);
 	return ret;
 }

drivers/nvme/host/nvme.h

@@ -152,6 +152,7 @@ enum nvme_quirks {
 struct nvme_request {
 	struct nvme_command	*cmd;
 	union nvme_result	result;
+	u8			genctr;
 	u8			retries;
 	u8			flags;
 	u16			status;
@@ -491,6 +492,49 @@ struct nvme_ctrl_ops {
 	int (*get_address)(struct nvme_ctrl *ctrl, char *buf, int size);
 };
 
+/*
+ * nvme command_id is constructed as such:
+ * | xxxx | xxxxxxxxxxxx |
+ *   gen    request tag
+ */
+#define nvme_genctr_mask(gen)			(gen & 0xf)
+#define nvme_cid_install_genctr(gen)		(nvme_genctr_mask(gen) << 12)
+#define nvme_genctr_from_cid(cid)		((cid & 0xf000) >> 12)
+#define nvme_tag_from_cid(cid)			(cid & 0xfff)
+
+static inline u16 nvme_cid(struct request *rq)
+{
+	return nvme_cid_install_genctr(nvme_req(rq)->genctr) | rq->tag;
+}
+
+static inline struct request *nvme_find_rq(struct blk_mq_tags *tags,
+		u16 command_id)
+{
+	u8 genctr = nvme_genctr_from_cid(command_id);
+	u16 tag = nvme_tag_from_cid(command_id);
+	struct request *rq;
+
+	rq = blk_mq_tag_to_rq(tags, tag);
+	if (unlikely(!rq)) {
+		pr_err("could not locate request for tag %#x\n",
+			tag);
+		return NULL;
+	}
+	if (unlikely(nvme_genctr_mask(nvme_req(rq)->genctr) != genctr)) {
+		dev_err(nvme_req(rq)->ctrl->device,
+			"request %#x genctr mismatch (got %#x expected %#x)\n",
+			tag, genctr, nvme_genctr_mask(nvme_req(rq)->genctr));
+		return NULL;
+	}
+	return rq;
+}
+
+static inline struct request *nvme_cid_to_rq(struct blk_mq_tags *tags,
+                u16 command_id)
+{
+	return blk_mq_tag_to_rq(tags, nvme_tag_from_cid(command_id));
+}
+
 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
 void nvme_fault_inject_init(struct nvme_fault_inject *fault_inj,
 			    const char *dev_name);
@@ -588,7 +632,8 @@ static inline void nvme_put_ctrl(struct nvme_ctrl *ctrl)
 
 static inline bool nvme_is_aen_req(u16 qid, __u16 command_id)
 {
-	return !qid && command_id >= NVME_AQ_BLK_MQ_DEPTH;
+	return !qid &&
+		nvme_tag_from_cid(command_id) >= NVME_AQ_BLK_MQ_DEPTH;
 }
 
 void nvme_complete_rq(struct request *req);

drivers/nvme/host/pci.c

@@ -1010,7 +1010,7 @@ static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx)
 		return;
 	}
 
-	req = blk_mq_tag_to_rq(nvme_queue_tagset(nvmeq), command_id);
+	req = nvme_find_rq(nvme_queue_tagset(nvmeq), command_id);
 	if (unlikely(!req)) {
 		dev_warn(nvmeq->dev->ctrl.device,
 			"invalid id %d completed on queue %d\n",

drivers/nvme/host/rdma.c

@@ -1730,10 +1730,10 @@ static void nvme_rdma_process_nvme_rsp(struct nvme_rdma_queue *queue,
 	struct request *rq;
 	struct nvme_rdma_request *req;
 
-	rq = blk_mq_tag_to_rq(nvme_rdma_tagset(queue), cqe->command_id);
+	rq = nvme_find_rq(nvme_rdma_tagset(queue), cqe->command_id);
 	if (!rq) {
 		dev_err(queue->ctrl->ctrl.device,
-			"tag 0x%x on QP %#x not found\n",
+			"got bad command_id %#x on QP %#x\n",
 			cqe->command_id, queue->qp->qp_num);
 		nvme_rdma_error_recovery(queue->ctrl);
 		return;

drivers/nvme/host/tcp.c

@@ -487,11 +487,11 @@ static int nvme_tcp_process_nvme_cqe(struct nvme_tcp_queue *queue,
 {
 	struct request *rq;
 
-	rq = blk_mq_tag_to_rq(nvme_tcp_tagset(queue), cqe->command_id);
+	rq = nvme_find_rq(nvme_tcp_tagset(queue), cqe->command_id);
 	if (!rq) {
 		dev_err(queue->ctrl->ctrl.device,
-			"queue %d tag 0x%x not found\n",
-			nvme_tcp_queue_id(queue), cqe->command_id);
+			"got bad cqe.command_id %#x on queue %d\n",
+			cqe->command_id, nvme_tcp_queue_id(queue));
 		nvme_tcp_error_recovery(&queue->ctrl->ctrl);
 		return -EINVAL;
 	}
@@ -508,11 +508,11 @@ static int nvme_tcp_handle_c2h_data(struct nvme_tcp_queue *queue,
 {
 	struct request *rq;
 
-	rq = blk_mq_tag_to_rq(nvme_tcp_tagset(queue), pdu->command_id);
+	rq = nvme_find_rq(nvme_tcp_tagset(queue), pdu->command_id);
 	if (!rq) {
 		dev_err(queue->ctrl->ctrl.device,
-			"queue %d tag %#x not found\n",
-			nvme_tcp_queue_id(queue), pdu->command_id);
+			"got bad c2hdata.command_id %#x on queue %d\n",
+			pdu->command_id, nvme_tcp_queue_id(queue));
 		return -ENOENT;
 	}
 
@@ -606,7 +606,7 @@ static int nvme_tcp_setup_h2c_data_pdu(struct nvme_tcp_request *req,
 	data->hdr.plen =
 		cpu_to_le32(data->hdr.hlen + hdgst + req->pdu_len + ddgst);
 	data->ttag = pdu->ttag;
-	data->command_id = rq->tag;
+	data->command_id = nvme_cid(rq);
 	data->data_offset = cpu_to_le32(req->data_sent);
 	data->data_length = cpu_to_le32(req->pdu_len);
 	return 0;
@@ -619,11 +619,11 @@ static int nvme_tcp_handle_r2t(struct nvme_tcp_queue *queue,
 	struct request *rq;
 	int ret;
 
-	rq = blk_mq_tag_to_rq(nvme_tcp_tagset(queue), pdu->command_id);
+	rq = nvme_find_rq(nvme_tcp_tagset(queue), pdu->command_id);
 	if (!rq) {
 		dev_err(queue->ctrl->ctrl.device,
-			"queue %d tag %#x not found\n",
-			nvme_tcp_queue_id(queue), pdu->command_id);
+			"got bad r2t.command_id %#x on queue %d\n",
+			pdu->command_id, nvme_tcp_queue_id(queue));
 		return -ENOENT;
 	}
 	req = blk_mq_rq_to_pdu(rq);
@@ -703,7 +703,7 @@ static int nvme_tcp_recv_data(struct nvme_tcp_queue *queue, struct sk_buff *skb,
 {
 	struct nvme_tcp_data_pdu *pdu = (void *)queue->pdu;
 	struct request *rq =
-		blk_mq_tag_to_rq(nvme_tcp_tagset(queue), pdu->command_id);
+		nvme_cid_to_rq(nvme_tcp_tagset(queue), pdu->command_id);
 	struct nvme_tcp_request *req = blk_mq_rq_to_pdu(rq);
 
 	while (true) {
@@ -796,8 +796,8 @@ static int nvme_tcp_recv_ddgst(struct nvme_tcp_queue *queue,
 	}
 
 	if (pdu->hdr.flags & NVME_TCP_F_DATA_SUCCESS) {
-		struct request *rq = blk_mq_tag_to_rq(nvme_tcp_tagset(queue),
-						pdu->command_id);
+		struct request *rq = nvme_cid_to_rq(nvme_tcp_tagset(queue),
+					pdu->command_id);
 
 		nvme_tcp_end_request(rq, NVME_SC_SUCCESS);
 		queue->nr_cqe++;

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;
 		}