linux-kernel - Re: [PATCH] mmc: core: Add error check to avoid kernel panic caused by NULL pointer

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Date:   Tue, 16 Jun 2020 13:26:10 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Corey Gao <gaoce123@...il.com>
Cc:     "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: core: Add error check to avoid kernel panic caused
 by NULL pointer

On Tue, 2 Jun 2020 at 19:31, Corey Gao <gaoce123@...il.com> wrote:
>
> If __mmc_start_req(host, mrq) fails with error, the mrq->cmd->mrq will
> be NULL. This will cause kernel panic in the following
> mmc_wait_for_req_done(host, mrq). Add error check to cancle unnecessary
> mmc_wait_for_req_done(host, mrq) if __mmc_start_req(host, mrq) fails.

The above is a bit hard for me to follow, can you please try to
elaborate on the problem. Moreover, please, provide a stack trace, as
that is easier to follow for me.

Kind regards
Uffe

>
> Signed-off-by: Corey Gao <gaoce123@...il.com>
> ---
>  drivers/mmc/core/core.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 2553d903a82b..b13b484e64aa 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -734,9 +734,11 @@ EXPORT_SYMBOL(mmc_start_req);
>   */
>  void mmc_wait_for_req(struct mmc_host *host, struct mmc_request *mrq)
>  {
> -       __mmc_start_req(host, mrq);
> +       int err;
>
> -       if (!mrq->cap_cmd_during_tfr)
> +       err = __mmc_start_req(host, mrq);
> +
> +       if (!mrq->cap_cmd_during_tfr && !err)
>                 mmc_wait_for_req_done(host, mrq);
>  }
>  EXPORT_SYMBOL(mmc_wait_for_req);
> --
> 2.17.1
>