linux-kernel - Re: use-after-free in __perf_install_in

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Date:	Fri, 4 Dec 2015 22:00:21 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: use-after-free in __perf_install_in_context

On Fri, Dec 4, 2015 at 9:32 PM, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> On Fri, Dec 04, 2015 at 09:04:35PM +0100, Dmitry Vyukov wrote:
>> Hello,
>>
>> While running syzkaller fuzzer I am seeing lots of the following
>> use-after-free reports. Unfortunately all my numerous attempts to
>> reproduce them in a controlled environment failed. They pop up during
>> fuzzing periodically (once in several hours in a single VM), but
>> whenever I try to stress-replay what happened in the VM before the
>> report, the use-after-free does not reproduce. Can somebody
>> knowledgeable in perf subsystem look at the report? Maybe it is
>> possible to figure out what happened based purely on the report. I can
>> pretty reliably test any proposed fixes.
>> All reports look like this one. Then it is usually followed by other
>> reports and eventually kernel hangs or dies. What happens in the
>> fuzzer is essentially random syscalls with random arguments, tasks
>> born and die concurrently and so on. I was able to reproduce it by
>> restricting syscalls only to perf_event_open, perf ioctls and bpf
>> syscall.
>
> For the sake of trying to narrow it down:
> does the error disappear when you stop using bpf syscall in your fuzzing?
> If yes, then I could have missed some interaction between perf_event_free,
> kprobe free and bpf_prog_free.
> There was a race there before.
> May be there is still something else.


It is a good question. I will test it.
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