From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1755853AbbJ1SGU (ORCPT <rfc822;w@1wt.eu>);
	Wed, 28 Oct 2015 14:06:20 -0400
Received: from mx1.redhat.com ([209.132.183.28]:37095 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751673AbbJ1SGT (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 28 Oct 2015 14:06:19 -0400
Date: Wed, 28 Oct 2015 20:02:35 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Pedro Alves <palves@redhat.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Jan Kratochvil <jan.kratochvil@redhat.com>,
        Julien Tinnes <jln@google.com>, Kees Cook <keescook@google.com>,
        Kostya Serebryany <kcc@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        Robert Swiecki <swiecki@google.com>,
        Roland McGrath <roland@hack.frob.com>, syzkaller@googlegroups.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "gdb@sourceware.org" <gdb@sourceware.org>
Subject: Re: [PATCH 1/2] wait/ptrace: always assume __WALL if the child is
	traced
Message-ID: <20151028190235.GA31914@redhat.com>
References: <20151020171754.GA29304@redhat.com> <20151020153155.e03f4219da4014efe6f810b0@linux-foundation.org> <5627EE9E.8040600@redhat.com> <5627F607.4050506@redhat.com> <20151021214703.GA1810@redhat.com> <CAK1hOcP027FAWg5uVDjiFDC+0=dGu5JFJcy9Jij4dY8SBnT4MA@mail.gmail.com> <20151025155440.GB2043@redhat.com> <562E17D8.4000108@redhat.com> <20151028161152.GA24042@redhat.com> <5630ED16.50900@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5630ED16.50900@redhat.com>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 10/28, Pedro Alves wrote:
>
> On 10/28/2015 04:11 PM, Oleg Nesterov wrote:
> > On 10/26, Pedro Alves wrote:
> >>
> >> (Also, in the original test case, if the child gets/raises a signal or execs
> >> before exiting, the bash/init/whatever process won't be issuing PTRACE_CONT,
> >> and the child will thus end up stuck (though should be SIGKILLable,
> >
> > Oh, but if it is killable everything is fine. How does this differ from the
> > case when, say, you jusr reparent to init and do kill(getpid(), SIGSTOP) ?
>
> The difference is that if the child called PTRACE_TRACEME, then it goes
> to ptrace-stop instead and no amount of SIGCONT unstucks it -- the only way
> out is force killing.  I agree it's not a major issue as there's a way out
> (and thus made it a parens), but I wouldn't call it nice either.

IOW, the difference is that it is TASK_TRACED, not TASK_STOPPED. I agree,
this is not nice. But this is not nice simply because PTRACE_TRACEME is
not nice.

> >> All this because PTRACE_TRACEME is broken by design
> >
> > Heh. I agree. But we can't fix it now.
>
> Perhaps the man page could document it as deprecated, suggesting
> PTRACE_ATTACH/PTRACE_SEIZE instead?

I don't know. but I won't mind if you mark PTRACE_ATTACH as deprecated
too ;) PTRACE_SEIZE can be used instead and it doesn't abuse SIGSTOP.

Oleg.