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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 2017-03-14 15:10 +0100
Message-ID <tkVjb-1eJ-13@gated-at.bofh.it> (permalink)
References (1 earlier) <ti0S5-lW-1@gated-at.bofh.it> <tinYm-6Q-23@gated-at.bofh.it> <tiohI-h2-23@gated-at.bofh.it> <tirfA-2oi-15@gated-at.bofh.it> <tkUds-cW-25@gated-at.bofh.it>
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On 03/14, Peter Zijlstra wrote:
>
> Yes, this looks buggy. But I cannot explain how that would result in the
> observed use-after-free.

Yes...

Suppose that copy_process() fails after perf_event_init_task(). In this
case perf_event_free_task() does put_ctx(), but if this ctx has another
reference (ctx->refcount > 1) then ctx->task will point to the already
freed task, copy_process() does free_task() at the end of error path.
And we can't replace it with put_task_struct().

I am looking at TASK_TOMBSTONE, perhaps perf_event_free_task() should
use it too?

Oleg.

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Thread

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
          Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 14:00 +0100
            Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 14:30 +0100
              Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 14:50 +0100
            Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 15:10 +0100
              Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 15:10 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 15:40 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 16:10 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 16:10 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 16:40 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 16:50 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 16:30 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 18:40 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-15 17:50 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-16 13:10 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-16 15:00 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-16 17:50 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 16:30 +0100

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