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From: Oleg Nesterov <oleg@redhat.com>
To: "Jürg Billeter" <j@bitron.ch>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Eric Biederman <ebiederm@xmission.com>,
	linux-api@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] prctl: add PR_[GS]ET_KILLABLE
Date: Fri, 3 Aug 2018 14:14:07 +0200
Message-ID: <20180803121406.GB13794@redhat.com> (raw)
In-Reply-To: <7f7c57230e0279f4599bf13ae1d1d449d76ac232.camel@bitron.ch>

On 08/03, Jürg Billeter wrote:
>
> On Wed, 2018-08-01 at 16:19 +0200, Oleg Nesterov wrote:
> > On 07/31, Jürg Billeter wrote:
> > >
> > > > Could you explain your use-case? Why a shell wants to use
> > > > CLONE_NEWPID?
> > >
> > > To guarantee that there won't be any runaway processes, i.e., ensure
> > > that no descendants (background helper daemons or misbehaving
> > > processes) survive when the child process is terminated.
> >
> > We already have PR_SET_CHILD_SUBREAPER.
> >
> > Perhaps we can finally add PR_KILL_MY_DESCENDANTS_ON_EXIT? This was already
> > discussed some time ago, but I can't find the previous discussion... Simple
> > to implement.
>
> This would definitely be an option. You mentioned it last October in
> the PR_SET_PDEATHSIG_PROC discussion¹. However, as PID namespaces
> already exist and appear to be a good fit for the most part,

Sure, if CLONE_NEWPID fits your needs you can use it,

> I think it
> makes sense to just add the missing pieces to PID namespaces instead of
> duplicating part of the PID namespace functionality.

Again, I am not arguing with your change.

PR_KILL_MY_DESCENDANTS_ON_EXIT can make sense just like PR_SET_CHILD_SUBREAPER
even if PID namespace functionality implies both. Simply because CLONE_NEWPID
is not necessarily the best tool, if nothing else you do not necessarily want
the pid isolation.

> Also, based on Eric's comment in that other discussion about
> no_new_privs not being allowed to increase the attack surface,
> PR_KILL_MY_DESCENDANTS_ON_EXIT might require CAP_SYS_ADMIN as well (due
> to setuid children).

No, no, the exiting parent should simply do group_send_sig_info(SIGKILL)
for every descendant and rely on check_kill_permission().

OK, lets forget it for now.

Oleg.


  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-30  7:52 [PATCH] " Jürg Billeter
2018-07-30 10:17 ` Oleg Nesterov
2018-07-30 19:32   ` Jürg Billeter
2018-07-30 19:39     ` Thomas Gleixner
2018-07-31  7:03 ` [PATCH v2] " Jürg Billeter
2018-07-31 14:39   ` Oleg Nesterov
2018-07-31 16:12     ` Jürg Billeter
2018-08-01 14:19       ` Oleg Nesterov
2018-08-03 10:15         ` Jürg Billeter
2018-08-03 12:14           ` Oleg Nesterov [this message]
2018-08-03 13:34           ` Eric W. Biederman
2018-08-03 14:39             ` Jürg Billeter
2018-07-31 16:26 ` [PATCH] " Jann Horn
2018-08-01  7:43   ` Jürg Billeter
2018-08-01  7:56     ` Jann Horn
2018-08-03 14:40 ` [PATCH v3 1/2] fork: do not rely on SIGNAL_UNKILLABLE for init check Jürg Billeter
2018-08-03 14:40   ` [PATCH v3 2/2] prctl: add PR_[GS]ET_KILLABLE Jürg Billeter
2018-09-06 22:42     ` Andrew Morton

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