[PATCH] nvme-tcp: fix possible req->offset corruption

[Varun Prakash]

With commit db5ad6b7f8cd ("nvme-tcp: try to send request in queue_rq
context") r2t and response PDU can get processed while send function
is executing.

Current data digest send code uses req->offset after kernel_sendmsg(),
this creates a race condition where req->offset gets reset before it
is used in send function.

This can happen in two cases -
1. Target sends r2t PDU which resets req->offset.
2. Target send response PDU which completes the req and then req is
   used for a new command, nvme_tcp_setup_cmd_pdu() resets req->offset.

Fix this by storing req->offset in a local variable and using
this local variable after kernel_sendmsg().

Fixes: db5ad6b7f8cd ("nvme-tcp: try to send request in queue_rq context")
Signed-off-by: Varun Prakash <varun at chelsio.com>
---
 drivers/nvme/host/tcp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 22da856..2217897 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -1048,6 +1048,7 @@ static int nvme_tcp_try_send_data_pdu(struct nvme_tcp_request *req)
 static int nvme_tcp_try_send_ddgst(struct nvme_tcp_request *req)
 {
 	struct nvme_tcp_queue *queue = req->queue;
+	size_t offset = req->offset;
 	int ret;
 	struct msghdr msg = { .msg_flags = MSG_DONTWAIT };
 	struct kvec iov = {
@@ -1064,7 +1065,7 @@ static int nvme_tcp_try_send_ddgst(struct nvme_tcp_request *req)
 	if (unlikely(ret <= 0))
 		return ret;
 
-	if (req->offset + ret == NVME_TCP_DIGEST_LENGTH) {
+	if (offset + ret == NVME_TCP_DIGEST_LENGTH) {
 		nvme_tcp_done_send_req(queue);
 		return 1;
 	}
-- 
2.0.2