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Groups > linux.kernel > #1600546
| Path | csiph.com!aioe.org!bofh.it!news.nic.it!robomod |
|---|---|
| From | Peter Zijlstra <peterz@infradead.org> |
| Newsgroups | linux.kernel |
| Subject | Re: perf: use-after-free in perf_release |
| Date | Tue, 14 Mar 2017 16:10:01 +0100 |
| Message-ID | <tkWff-1T2-5@gated-at.bofh.it> (permalink) |
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| X-Original-Cc | Dmitry Vyukov <dvyukov@google.com>, Ingo Molnar <mingo@redhat.com>, Arnaldo Carvalho de Melo <acme@kernel.org>, Alexander Shishkin <alexander.shishkin@linux.intel.com>, LKML <linux-kernel@vger.kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, syzkaller <syzkaller@googlegroups.com> |
| X-Original-Date | Tue, 14 Mar 2017 16:02:41 +0100 |
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On Tue, Mar 14, 2017 at 03:30:11PM +0100, Oleg Nesterov wrote:
> But. perf_event_init_task() adds child_event to parent_event->child_list.
>
> If perf_event_release_kernel(parent_event) is called before copy_process()
> does perf_event_free_task() which (in particular) removes it from child_list,
> perf_event_release_kernel() can find this child_event and do get_ctx(ctx)
> (under the list_for_each_entry(child, &event->child_list, child_list) loop).
Right; the child_list is the only thing that is exposed. And yes, it
looks like that can interleave just right.
> Then it does put_ctx(ctx), but ctx->task can be already freed by
> copy_process()->free_task() in this case.
Task1 Task2
fork()
perf_event_init_task()
/* ... */
goto bad_fork_$foo;
/* ... */
perf_event_free_task()
mutex_lock(ctx->lock)
perf_free_event(B)
perf_event_release_kernel(A)
mutex_lock(A->child_mutex)
list_for_each_entry(child, ...) {
/* child == B */
ctx = B->ctx;
get_ctx(ctx);
mutex_unlock(A->child_mutex);
mutex_lock(A->child_mutex)
list_del_init(B->child_list)
mutex_unlock(A->child_mutex)
/* ... */
mutex_unlock(ctx->lock);
put_ctx() /* >0 */
free_task();
mutex_lock(ctx->lock);
mutex_lock(A->child_mutex);
/* ... */
mutex_unlock(A->child_mutex);
mutex_unlock(ctx->lock)
put_ctx() /* 0 */
ctx->task && !TOMBSTONE
put_task_struct() /* UAF */
Something like that, right?
Let me see if it makes sense to retain perf_event_free_task() at all;
maybe we should always do perf_event_exit_task().
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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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