linux-kernel - Re: [PATCH] drivers: block: rnbd: Handle generic ERR_PTR returns safely in find_and_get_or_create

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Message-ID: <CAMGffEmsJjeqW8DGnKapVyM0Gporn_UuDB2xNosRmD2GduGgzg@mail.gmail.com>
Date: Tue, 21 Oct 2025 10:01:57 +0200
From: Jinpu Wang <jinpu.wang@...os.com>
To: Ranganath V N <vnranganath.20@...il.com>
Cc: "Md. Haris Iqbal" <haris.iqbal@...os.com>, Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org, 
	linux-kernel@...r.kernel.org, skhan@...uxfoundation.org, 
	david.hunter.linux@...il.com, khalid@...nel.org, 
	linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] drivers: block: rnbd: Handle generic ERR_PTR returns
 safely in find_and_get_or_create_sess()

On Tue, Oct 21, 2025 at 8:21 AM Ranganath V N <vnranganath.20@...il.com> wrote:
>
> Fix the issue detected by the smatch tool.
> drivers/block/rnbd/rnbd-clt.c:1241 find_and_get_or_create_sess()
> error: 'sess' dereferencing possible ERR_PTR()
>
> find_and_get_or_create_sess() only checks for ERR_PTR(-ENOMEM) after
> calling find_or_create_sess(). In other encoded failures, the code
> may dereference the error pointer when accessing sess->nr_poll_queues,
> resulting ina kernel oops.
>
> By preserving the existing -ENOMEM behaviour and log unexpected
> errors to assist in debugging. This change eliminates a potential
> invalid pointer dereference without altering the function's logic
> or intenet.
>
> Tested by compiling using smatch tool.
Thx for the patch.
But I read the code again, find_or_create_sess -> alloc_sess, which
only return ERR_PTR(-ENOMEM) or a valid pointer.
I think this is just a false positive.
>
> Signed-off-by: Ranganath V N <vnranganath.20@...il.com>
> ---
>  drivers/block/rnbd/rnbd-clt.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
> index f1409e54010a..57ca694210b9 100644
> --- a/drivers/block/rnbd/rnbd-clt.c
> +++ b/drivers/block/rnbd/rnbd-clt.c
> @@ -1236,9 +1236,14 @@ find_and_get_or_create_sess(const char *sessname,
>         struct rtrs_clt_ops rtrs_ops;
>
>         sess = find_or_create_sess(sessname, &first);
> -       if (sess == ERR_PTR(-ENOMEM)) {
> -               return ERR_PTR(-ENOMEM);
> -       } else if ((nr_poll_queues && !first) ||  (!nr_poll_queues && sess->nr_poll_queues)) {
> +       if (IS_ERR(sess)) {
> +               err = PTR_ERR(sess);
> +               if (err != -ENOMEM)
> +                       pr_warn("rndb: find_or_create_sess(%s) failed with %d\n",
> +                               sessname, err);
> +               return ERR_PTR(err);
> +       }
> +       if ((nr_poll_queues && !first) ||  (!nr_poll_queues && sess->nr_poll_queues)) {
>                 /*
>                  * A device MUST have its own session to use the polling-mode.
>                  * It must fail to map new device with the same session.
>
> ---
> base-commit: 211ddde0823f1442e4ad052a2f30f050145ccada
> change-id: 20251021-rnbd_fix-9b478fb52403
>
> Best regards,
> --
> Ranganath V N <vnranganath.20@...il.com>
>