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
