linux-kernel - Re: [PATCH 1/3] ptrace: ptrace_reparented() should check same_thread

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Message-ID: <20110625134350.GU30101@htj.dyndns.org>
Date:	Sat, 25 Jun 2011 15:43:50 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	vda.linux@...glemail.com, jan.kratochvil@...hat.com,
	pedro@...esourcery.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ptrace: ptrace_reparented() should check
 same_thread_group()

Hello,

On Fri, Jun 24, 2011 at 05:34:06PM +0200, Oleg Nesterov wrote:
> exit_notify: we should respect ->exit_signal if the exiting leader
> is traced by any thread from the parent thread group. It is the
> child of the whole group, and we are going to send the signal to
> the whole group.

This seems correct.

> wait_task_zombie: without __WNOTHREAD do_wait() should do the same
> for any thread, only sys_ptrace() is "bound" to the single thread.
> However do_wait(WEXITED) succeeds but does not release a traced
> natural child unless the caller is the tracer.
>
> Test-case:
...
> Note that the main thread simply does
> 
> 	pid = fork();
> 	kill(pid, SIGKILL);
> 
> and then without the patch wait4(WEXITED) succeeds twice and reports
> WTERMSIG(stat) == SIGKILL.

This latter one is interesting to say the least.  Yes, wait(2) is
process-wide operation and should behave identically when for all
threads in the same process.

> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

This patch involves very subtle behavior change when the tracer is
multi-threaded && real parent of the tracee.  Slightly worrisome but
it is a bug fix and extremely fringe, so...

 Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun
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