On Mon, 4 Sep 2006, Andreas Hobein wrote:
>
> I've tested tracing child threads from the parent thread as well as tracing
> siblings and parent threads from a child. All tests where successful when
> reverting the above mentioned changes.
The problems tend to happen when the thread leader exits while one of the
sub-threads is being traced, and the tracer thread ends up being
re-parented to be the child of the traced thread (or something like that -
I forget the exact details).
There was also some problem with the tracer doing an exit() without
detaching, or something.
We may have fixed most of the problems since - Oleg has certainly been
cleaning up some of this, and it's possible that the problems we had are
ok now.
Even back when it was broken, _normal_ use never showed the problem (ie no
well-behaved ptrace use would cause anything bad to happen). But the
breakage was a local DoS attack, where you could either force an oops or a
unkillable process, I forget which.
There was an exploit for at least one of the exploits, so maybe somebody
could test that exploit together with the one-line revert.
That said, it sounds like both of the people who ever noticed this are
reasonably happy with their work-arounds, so I'm hoping we can simply
decide not to care, and just keep doing the simpler "you can't ptrace your
own thread group" thing. That rule simply avoids a lot of special cases.
Linus
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