linux-kernel - Re: [PATCH] pid: Add the judgment of whether ns is NULL in the find_pid

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Date:   Wed, 19 Jul 2023 19:46:29 +0800
From:   Xuewen Yan <xuewen.yan94@...il.com>
To:     Xuewen Yan <xuewen.yan@...soc.com>
Cc:     brauner@...nel.org, jack@...e.cz, keescook@...omium.org,
        peterz@...radead.org, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, di.shen@...soc.com
Subject: Re: [PATCH] pid: Add the judgment of whether ns is NULL in the find_pid_ns

Dear all

Is there any comment about this patch?

Thanks!

On Thu, Jul 13, 2023 at 3:58 PM Xuewen Yan <xuewen.yan@...soc.com> wrote:
>
> There is no the judgment of whether namspace is NULL in find_pid_ns.
> But there is a corner case when ns is null, for example: if user
> call find_get_pid when current is in exiting, the following stack would
> set thread_id be null:
> release_task
>     __exit_signal(p);
>         __unhash_process(tsk, group_dead);
>               detach_pid(p, PIDTYPE_PID);
>                   __change_pid(task, type, NULL);
>
> If user call find_get_pid at now, in find_vpid function, the
> task_active_pid_ns would return NULL. As a result, it would be
> error when access the ns in find_pid_ns.
>
> So add the judgment of whether ns is NULL in the find_pid_ns to
> prevent this case happen.
>
> Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
> ---
>  kernel/pid.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 6a1d23a11026..d4a9cb6f3eb9 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -308,6 +308,9 @@ void disable_pid_allocation(struct pid_namespace *ns)
>
>  struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
>  {
> +       if (!ns)
> +               return NULL;
> +
>         return idr_find(&ns->idr, nr);
>  }
>  EXPORT_SYMBOL_GPL(find_pid_ns);
> --
> 2.25.1
>