linux-kernel - Re: ptrace.2: PTRACE_KILL needs a stopped process too

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Message-ID: <4FAAEACF.3070405@redhat.com>
Date:	Wed, 09 May 2012 23:08:15 +0100
From:	Pedro Alves <palves@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Mike Frysinger <vapier@...too.org>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	pacman@...h.dhis.org, linux-man <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Tejun Heo <tj@...nel.org>,
	Jan Kratochvil <jan.kratochvil@...hat.com>
Subject: Re: ptrace.2: PTRACE_KILL needs a stopped process too

On 05/09/2012 09:12 PM, Oleg Nesterov wrote:

> tgkill() can kill the wrong process/thread too, although it lessens the risk.

> 
> But I don't really understand the problem. The traced thread can't go away

> until the tracer does wait/detach, and thus its pid can't be reused?


There's the non-leader thread execs and tracer didn't enable
PTRACE_O_TRACEEXEC case at least, while you try to kill the thread that just
execed, I think.  Though that's quite pedantic.  The tracer could prevent this
in other ways.

> May be, "by accident" above means something else, not pid reuse...


Pffft, who writes buggy code anyway?  ;-)

-- 
Pedro Alves
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