Re: perf: use-after-free in perf_release

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: perf: use-after-free in perf_release
Date	2017-03-07 18:50 +0100
Message-ID	<tirfA-2oi-15@gated-at.bofh.it> (permalink)
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On 03/07, Dmitry Vyukov wrote:
>
> On Tue, Mar 7, 2017 at 3:04 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> > On 03/06, Peter Zijlstra wrote:
> >>
> >> and this is a failed fork().
> >>
> >>
> >> However, inherited events don't have a filedesc to fput(), and
> >> similarly, a task that fails for has never been visible to attach a perf
> >> event to because it never hits the pid-hash.
> >
> > Yes, it is not visible to find_task_by_vpid() until copy_process() does
> > attach_pid(PIDTYPE_PID), and copy_process() can't fail after that.
>
>
> I would what is that that is failed in copy_process. Could it be
> perf_event_init_task itself? Maybe it leaves a pointer to p in some
> shared state on some error conditions?

I am looking at perf_event_init_task() too and I can't understand the
error handling...

perf_event_init_context() can return success even if inherit_task_group() in
the first list_for_each_entry(pinned_groups) fails, "ret" will be overwritten
by the 2nd list_for_each_entry(flexible_groups) loop. "inherited_all" should
be cleared, still this looks confusing at least.

inherit_event() returns NULL under is_orphaned_event() check, not ERR_PTR().
Is it correct?

Oleg.

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perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-06 11:00 +0100
  Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-06 13:20 +0100
    Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-06 13:20 +0100
      Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-06 13:30 +0100
        Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-06 13:40 +0100
          Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-06 13:50 +0100
  Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-06 14:30 +0100
    Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-06 14:40 +0100
      Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-07 10:30 +0100
        Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-07 10:50 +0100
          Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 12:50 +0100
        Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 11:40 +0100
      Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 10:50 +0100
    Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 14:20 +0100
      Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 15:10 +0100
    Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-07 15:10 +0100
      Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-07 15:30 +0100
        Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 18:40 +0100
        Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-07 18:50 +0100

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