Re: Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads

From: Linus Torvalds
Date: Tue Jun 22 2021 - 20:42:17 EST

On Tue, Jun 22, 2021 at 1:53 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
> Playing with it some more I think I have everything working working
> except for PTRACE_EVENT_SECCOMP (which can stay ptrace_event) and
> group_exit(2).
> Basically in exit sending yourself a signal and then calling do_exit
> from the signal handler is not unreasonable, as exit is an ordinary
> system call.

Ok, this is a bit odd, but I do like the concept of just making
ptrace_event just post a signal, and have all ptrace things always be
handled at signal time (or the special system call entry/exit, which
is fine too).

> For purposes of discussion this is my current draft implementation.

I didn't check what is so different about exit_group() that you left
that as an exercise for the reader, but if that ends up then removing
the whole "wait synchromously for ptrace" cases for good I don't
_hate_ this. It's a bit odd, but it would be really nice to limit
where ptrace picks up data.

We do end up doing that stuff in "get_signal()", and that means that
we have the interaction with io_uring calling it directly, but it's at
least not a new thing.