linux-kernel - Re: [PATCH] pid: Allow frozen userspace to reboot from non-init pid ns

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Date:   Fri, 29 Sep 2023 13:09:52 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Brian Geffon <bgeffon@...gle.com>
Cc:     Christian Brauner <brauner@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pid: Allow frozen userspace to reboot from non-init pid
 ns

On Fri, Sep 29, 2023 at 01:44:42PM -0400, Brian Geffon wrote:
> When the system has a frozen userspace, for example, during hibernation
> the child reaper task will also be frozen. Attmepting to deliver a
> signal to it to handle the reboot(2) will ultimately lead to the system
> hanging unless userspace is thawed.
> 
> This change checks if the current task is the suspending task and if so
> it will allow it to proceed with a reboot from the non-init pid ns.

I don't know the code flow too well here, but shouldn't init_pid_ns
always be doing the reboot regardless of anything else?

Also how is this syscall running if current is frozen? This feels weird
to me... shouldn't the frozen test be against pid_ns->child_reaper
instead of current?

-Kees

-- 
Kees Cook