[PATCH v2] nvmet: Avoid potential UAF in nvmet_req_complete()

[Damien Le Moal]

An nvme target ->queue_response() operation implementation may free the
request passed as argument. Such implementation potentially could result
in a use after free of the request pointer when percpu_ref_put() is
called in nvmet_req_complete().

Avoid such problem by using a local variable to save the sq pointer
before calling __nvmet_req_complete(), thus avoiding dereferencing the
req pointer after that function call.

Fixes: a07b4970f464 ("nvmet: add a generic NVMe target")
Cc: stable at vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal at opensource.wdc.com>
---

Changes from v1:
 * Added Fixes tag and cc stable

 drivers/nvme/target/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index f66ed13d7c11..3935165048e7 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -756,8 +756,10 @@ static void __nvmet_req_complete(struct nvmet_req *req, u16 status)
 
 void nvmet_req_complete(struct nvmet_req *req, u16 status)
 {
+	struct nvmet_sq *sq = req->sq;
+
 	__nvmet_req_complete(req, status);
-	percpu_ref_put(&req->sq->ref);
+	percpu_ref_put(&sq->ref);
 }
 EXPORT_SYMBOL_GPL(nvmet_req_complete);
 
-- 
2.39.2