[PATCH] nvmet: Fix a use-after-free

[Sagi Grimberg]

On 8/13/22 00:03, Bart Van Assche wrote:
> Fix the following use-after-free complaint triggered by blktests nvme/004:
> 
> BUG: KASAN: user-memory-access in blk_mq_complete_request_remote+0xac/0x350
> Read of size 4 at addr 0000607bd1835943 by task kworker/13:1/460
> Workqueue: nvmet-wq nvme_loop_execute_work [nvme_loop]
> Call Trace:
>   show_stack+0x52/0x58
>   dump_stack_lvl+0x49/0x5e
>   print_report.cold+0x36/0x1e2
>   kasan_report+0xb9/0xf0
>   __asan_load4+0x6b/0x80
>   blk_mq_complete_request_remote+0xac/0x350
>   nvme_loop_queue_response+0x1df/0x275 [nvme_loop]
>   __nvmet_req_complete+0x132/0x4f0 [nvmet]
>   nvmet_req_complete+0x15/0x40 [nvmet]
>   nvmet_execute_io_connect+0x18a/0x1f0 [nvmet]
>   nvme_loop_execute_work+0x20/0x30 [nvme_loop]
>   process_one_work+0x56e/0xa70
>   worker_thread+0x2d1/0x640
>   kthread+0x183/0x1c0
>   ret_from_fork+0x1f/0x30
> 
> Cc: stable at vger.kernel.org
> Fixes: a07b4970f464 ("nvmet: add a generic NVMe target")
> Signed-off-by: Bart Van Assche <bvanassche at acm.org>
> ---
>   drivers/nvme/target/core.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
> index a1345790005f..7f4083cf953a 100644
> --- a/drivers/nvme/target/core.c
> +++ b/drivers/nvme/target/core.c
> @@ -735,6 +735,8 @@ static void nvmet_set_error(struct nvmet_req *req, u16 status)
>   
>   static void __nvmet_req_complete(struct nvmet_req *req, u16 status)
>   {
> +	struct nvmet_ns *ns = req->ns;
> +
>   	if (!req->sq->sqhd_disabled)
>   		nvmet_update_sq_head(req);
>   	req->cqe->sq_id = cpu_to_le16(req->sq->qid);
> @@ -745,9 +747,9 @@ static void __nvmet_req_complete(struct nvmet_req *req, u16 status)
>   
>   	trace_nvmet_req_complete(req);
>   
> -	if (req->ns)
> -		nvmet_put_namespace(req->ns);
>   	req->ops->queue_response(req);
> +	if (ns)
> +		nvmet_put_namespace(ns);

Why did the put change position?
I'm not exactly clear what was used-after-free here..

>   }
>   
>   void nvmet_req_complete(struct nvmet_req *req, u16 status)