linux-kernel - Re: [Bug 210655] ptrace.2: documentation is incorrect about access checking threads in same thread group

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Date:   Tue, 15 Dec 2020 19:34:29 +0100
From:   "Alejandro Colomar (man-pages)" <alx.manpages@...il.com>
To:     Ted Estes <ted@...twarecrafters.com>,
        Pavel Emelyanov <xemul@...nvz.org>,
        Oleg Nesterov <oleg@...sign.ru>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Kees Cook <keescook@...omium.org>, Jann Horn <jann@...jh.net>
Cc:     linux-man <linux-man@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [Bug 210655] ptrace.2: documentation is incorrect about access
 checking threads in same thread group

Hi Ted,

On 12/15/20 7:31 PM, Ted Estes wrote:
> 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 for all the details and links!
I'll fix the page.

Thanks,

Alex

> 
> 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
>>
> 

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es