linux-kernel - Re: [PATCH v2 1/1] prctl: add PR_{GET,SET}_KILL_DESCENDANTS_ON

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Message-ID: <87bm66u1j5.fsf@oldenburg.str.redhat.com>
Date:   Fri, 30 Nov 2018 14:40:14 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Jürg Billeter <j@...ron.ch>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] prctl: add PR_{GET,SET}_KILL_DESCENDANTS_ON_EXIT

* Jürg Billeter:

> This introduces a new thread group flag that can be set by calling
>
>     prctl(PR_SET_KILL_DESCENDANTS_ON_EXIT, 1, 0, 0, 0)
>
> When a thread group exits with this flag set, it will send SIGKILL to
> all descendant processes.  This can be used to prevent stray child
> processes.
>
> This flag is cleared on privilege gaining execve(2) to ensure an
> unprivileged process cannot get a privileged process to send SIGKILL.

So this is inherited across regular execve?  I'm not sure that's a good
idea.

> Descendants that are orphaned and reparented to an ancestor of the
> current process before the current process exits, will not be killed.
> PR_SET_CHILD_SUBREAPER can be used to contain orphaned processes.

For double- or triple-forking daemons, the reparenting will be racy, if
I understand things correctly.

Thanks,
Florian