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Sender: Ted Estes <check.switch.26@gmail.com>
Subject: Re: [Bug 210655] ptrace.2: documentation is incorrect about access
 checking threads in same thread group
To:     "Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>,
        Pavel Emelyanov <xemul@openvz.org>,
        Oleg Nesterov <oleg@tv-sign.ru>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Kees Cook <keescook@chromium.org>, Jann Horn <jann@thejh.net>
Cc:     linux-man <linux-man@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
References: <feef4f9a-4ed8-8a2e-d330-88e7f516faae@gmail.com>
From:   Ted Estes <ted@softwarecrafters.com>
Message-ID: <b416e106-c11d-1471-de3d-fb9d5b1b6747@softwarecrafters.com>
Date:   Tue, 15 Dec 2020 12:31:11 -0600
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Per my research on the topic, the error is in the manual page.  The 
behavior of ptrace(2) was intentionally changed to prohibit attaching to 
a thread in the same group.  Apparently, there were a number of 
ill-behaved edge cases.

I found this email thread on the subject: 
https://lkml.org/lkml/2006/8/31/241

Thank you.
--Ted Estes

On 12/15/2020 11:01 AM, Alejandro Colomar (man-pages) wrote:
> Hi,
>
> There's a bug report: https://bugzilla.kernel.org/show_bug.cgi?id=210655
>
> [[
> Under "Ptrace access mode checking", the documentation states:
>    "1. If the calling thread and the target thread are in the same thread
> group, access is always allowed."
>
> This is incorrect. A thread may never attach to another in the same group.
>
> Reference, ptrace_attach()
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/kernel/ptrace.c?h=v5.9.14#n380
> ]]
>
> I just wanted to make sure that it is a bug in the manual page, and not
> in the implementation.
>
>
> Thanks,
>
> Alex
>