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

[Ted Estes]

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