linux-kernel - Re: [PATCH] drivers: nvme: target: core: deref after null

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Date: Mon, 10 Jun 2024 04:34:00 +0000
From: Chaitanya Kulkarni <chaitanyak@...dia.com>
To: Alexander Sapozhnikov <alsp705@...il.com>
CC: "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
	Chaitanya Kulkarni <chaitanyak@...dia.com>, Sagi Grimberg <sagi@...mberg.me>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Christoph
 Hellwig <hch@....de>, "lvc-project@...uxtesting.org"
	<lvc-project@...uxtesting.org>
Subject: Re: [PATCH] drivers: nvme: target: core: deref after null

On 6/7/24 06:43, Alexander Sapozhnikov wrote:
> From: Alexandr Sapozhnikov <alsp705@...il.com>
>
> After having been compared to a NULL value at core.c:813,
> pointer '(**sq->ctrl).sqs' is dereferenced at core.c:838.

really didn't understand the NULL check mentioned above :-

  812          */
  813         if (ctrl && ctrl->sqs && ctrl->sqs[0] == sq)
  814                 nvmet_async_events_failall(ctrl);

from what I know it checks the non NULL ctrl->sqs and then
validates the sq is admin queue before calling failing the async
events ...

> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Signed-off-by: Alexandr Sapozhnikov <alsp705@...il.com>
> ---
>   drivers/nvme/target/core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
> index 06f0c587f343..5a67d2bc0c55 100644
> --- a/drivers/nvme/target/core.c
> +++ b/drivers/nvme/target/core.c
> @@ -827,7 +827,7 @@ void nvmet_sq_destroy(struct nvmet_sq *sq)
>   	 */
>   	ctrl = sq->ctrl;
>   
> -	if (ctrl) {
> +	if (ctrl && ctrl->sqs) {
>   		/*
>   		 * The teardown flow may take some time, and the host may not
>   		 * send us keep-alive during this period, hence reset the

do we need more fine grained check where ctrl->sqs is actually
accessed :-

diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index 06f0c587f343..a70cad5a6262 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -835,7 +835,8 @@ void nvmet_sq_destroy(struct nvmet_sq *sq)
                  * controller teardown as a result of a keep-alive 
expiration.
                  */
                 ctrl->reset_tbkas = true;
-               sq->ctrl->sqs[sq->qid] = NULL;
+               if (sq->ctrl->sqs)
+                       sq->ctrl->sqs[sq->qid] = NULL;
                 nvmet_ctrl_put(ctrl);
                 sq->ctrl = NULL; /* allows reusing the queue later */
         }

-ck