linux-kernel - Re: [RESEND PATCH] prctl: add PR_[GS]ET_PDEATHSIG

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Date:   Sun, 08 Oct 2017 19:47:25 +0200
From:   Jürg Billeter <j@...ron.ch>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Filipe Brandenburger <filbranden@...gle.com>,
        David Wilcox <davidvsthegiant@...il.com>, hansecke@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] prctl: add PR_[GS]ET_PDEATHSIG_PROC

On Thu, 2017-10-05 at 18:27 +0200, Oleg Nesterov wrote:
> On 10/03, Jürg Billeter wrote:
> > 
> > My use case is to provide a way for a process to spawn a child and
> > ensure that no descendants survive when that child dies.  Avoiding
> > runaway processes is desirable in many situations.  My motivation is
> > very lightweight (nested) sandboxing (every process is potentially
> > sandboxed).
> > 
> > I.e., pid namespaces would be a pretty good fit (assuming they are
> > sufficiently lightweight) but CLONE_NEWPID
> 
> sorry if this was already discussed, I didn't read this thread yet...
> 
> if CLONE_NEWPID is not suitable for any reason. We already have
> PR_SET_CHILD_SUBREAPER. Perhaps we can simply add another
> PR_SET_KILL_ALL_DESCEDANTS_ON_EXIT? we can use walk_process_tree()
> to send SIGKILL.

Yes, this is an option.  However, after the discussion in this thread I
believe it would be better to drop the CAP_SYS_ADMIN requirement for
CLONE_NEWPID (when no_new_privs is set) as this would avoid adding
another API and code path for a similar effect.  I'm interested in
possible security concerns about such a change.  Adding Andy Lutomirski
to cc.

Jürg