Re: Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads

[Linus Torvalds]

On Mon, Jun 21, 2021 at 4:23 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
>         How would it help e.g. oopsen on the way out of timer interrupts?
> IMO we simply shouldn't allow ptrace access if the tracee is in that kind
> of state, on any architecture...

Yeah no, we can't do the "wait for ptrace" when the exit is due to an
oops. Although honestly, we have other cases like that where do_exit()
isn't 100% robust if you kill something in an interrupt. Like all the
locks it leaves locked etc.

So do_exit() from a timer interrupt is going to cause problems
regardless. I agree it's probably a good idea to try to avoid causing
even more with the odd ptrace thing, but I don't think ptrace_event is
some really "fundamental" problem at that point - it's just one detail
among many many.

So I was more thinking of the debug patch for m68k to catch all the
_regular_ cases, and all the other random cases of ptrace_event() or
ptrace_notify().

Although maybe we've really caught them all. The exit case was clearly
missing, and the thread fork case was scrogged. There are patches for
the known problems. The patches I really don't like are the
verification ones to find any unknown ones..

            Linus