linux-kernel - Re: PT_EXITKILL (Was: pdeath

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Message-ID: <20121108124424.GB20917@redhat.com>
Date:	Thu, 8 Nov 2012 13:44:24 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pedro Alves <palves@...hat.com>
Cc:	Amnon Shiloh <u3557@...o.sublimeip.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Chris Evans <scarybeasts@...il.com>,
	David Howells <dhowells@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>, u3557@...lix.com.au,
	security@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: PT_EXITKILL (Was: pdeath_signal)

On 11/08, Pedro Alves wrote:
>
> On 11/07/2012 03:09 PM, Oleg Nesterov wrote:
>
> > OK. Please see the untested/uncompiled (but trivial) patch below
> >
> > 	- it adds PTRACE_O_EXITKILL. A better name?
> >
> > 	- A better numeric value? Note that the new option is not equal to
> > 	  the last-ptrace-option << 1. Because currently all options have
> > 	  the event, and the new one starts the eventless group. 1 << 16
> > 	  means we have the room for 8 more events.
> >
> > 	- it needs the convincing changelog for akpm
>
>
> If this isn't inherited by the ptrace child's children, a fork child can
> end up detached if the tracer dies before it had a chance of setting
> the PTRACE_O_EXITKILL on the new auto-attached child.

It is copied like the other options.

> Which sounds like another argument for PTRACE_O_INHERIT, as in:
> http://sourceware.org/ml/archer/2011-q1/msg00026.html

	The point of PTRACE_O_INHERIT would be to attach newly-created threads and
	children without causing an event stop and the attendant overhead.

this is another thing, I guess.

> (it sounds like you need to use PTRACE_SEIZE+options too to plug
> the race between PTRACE_ME/PTRACE_ATTACH and
> setting PTRACE_SETOPTIONS).

Agreed, PTRACE_SEIZE+options is better.

> (For completeness, Windows' age old equivalent,
> DebugSetProcessKillOnExit, it a tracer option, not tracee option, though
> that's not as flexible.)

Thanks ;)

Oleg.

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