linux-kernel - Re: [PATCH] pid: Add a judgment for ns null in pid_nr

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Message-ID: <CAGudoHEoK9f=M6-iOL5yHqK=o4wiJW_78t88BEwsAksAW5HNqQ@mail.gmail.com>
Date: Mon, 1 Sep 2025 17:44:46 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Christian Brauner <brauner@...nel.org>, Xiang Gao <gxxa03070307@...il.com>, joel.granados@...nel.org, 
	lorenzo.stoakes@...cle.com, linux-kernel@...r.kernel.org, 
	gaoxiang17 <gaoxiang17@...omi.com>, Liam.Howlett@...cle.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH] pid: Add a judgment for ns null in pid_nr_ns

On Mon, Sep 1, 2025 at 5:32 PM Oleg Nesterov <oleg@...hat.com> wrote:
>
> ping...
>
> We need either
>
>   [1/1] pid: Add a judgment for ns null in pid_nr_ns
>   https://git.kernel.org/vfs/vfs/c/006568ab4c5c
>
> or
>
>   [1/4] pid: make __task_pid_nr_ns(ns => NULL) safe for zombie callers
>   https://git.kernel.org/vfs/vfs/c/abdfd4948e45
>
> in any case imo the changelog should explain why do we care
> to check ns != NUll, "Sometimes null is returned for task_active_pid_ns"
> doesn't look like a good explanation...
>

Since I caught this a stray patchset I'll bite: given the totally
arbitrary task struct in an irq handler, why even allow querying it
from that level? The task is literally random, and even possibly dead
as in this crash report.

To my reading the code which runs into woes here is private to a
vendor. Maybe I missed something, but I don't see a justification for
querying the task in an irq handler to begin with (and per above I
don't understand what the point is).

That is to say, if this was up to me, I would at best assert we are in
the process context and that ns is not NULL. As a result I would very
much *ban* the call as reported here, unless there is a good reason to
make it work (what is it?).

That's my side rant, feel free to ignore. :->

-- 
Mateusz Guzik <mjguzik gmail.com>