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

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Message-ID: <20230725-hemmschwelle-braten-481527898001@brauner>
Date:   Tue, 25 Jul 2023 10:26:19 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Xuewen Yan <xuewen.yan@...soc.com>
Cc:     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

On Thu, Jul 13, 2023 at 03:17:13PM +0800, Xuewen Yan 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

I fail to see how this can happen. The code you're referencing is in
release_task(). If current has gone through that then current obviously
can't call find_vpid() on itself anymore or anything else for that
matter.