Re: perf: use-after-free in perf_release

From: Dmitry Vyukov <dvyukov@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: 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>,
	Oleg Nesterov <oleg@redhat.com>
Subject: Re: perf: use-after-free in perf_release
Date: Tue, 7 Mar 2017 10:43:32 +0100	[thread overview]
Message-ID: <CACT4Y+YAXyvaoJiChNgePaa=3X4ZMiWb++zuE3Gi9b2VhSu9fQ@mail.gmail.com> (raw)
In-Reply-To: <20170307093759.GU6500@twins.programming.kicks-ass.net>

On Tue, Mar 7, 2017 at 10:37 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Mar 07, 2017 at 10:26:20AM +0100, Dmitry Vyukov wrote:
>> On Tue, Mar 7, 2017 at 10:08 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>> > On Mon, Mar 06, 2017 at 02:34:50PM +0100, Dmitry Vyukov wrote:
>> >> FWIW here are 2 syzkaller programs that triggered the bug:
>> >> https://gist.githubusercontent.com/dvyukov/d67f980050589775237a7fbdff226bec/raw/4bca72861cb2ede64059b6dad403e19f425a361f/gistfile1.txt
>> >
>> > Hurm, previously your gistfile thingies were actual C, but this thing is
>> > gibberish. How do I run it?
>>
>> The same way we did it here:
>> https://groups.google.com/d/msg/syzkaller/MHXa-o8foyc/yrGfDOrwAQAJ
>
> Oh right, completely forgot about that. The last gistfile stuff I found
> in my history were actual C files.
>
>> This will run it in infinite loop in 10 parallel processes:
>> ./syz-execprog -repeat=0 -procs=10 -sandbox=namespace gistfile1.txt
>> -sandbox=namespace will require CONFIG_USER_NS=y, I am not sure if it
>> is actually required, but that's how bots triggered it. You can do
>> -sandbox=none as well.
>
> I still have an ancient syzcaller; -sandbox doesn't exist and I needed
> to add -executor=bin/syz-executor but now it appears to run.
>
> I'll go up procs, 10 is somewhat low I feel.
>
>
> ---
>
> root@ivb-ep:~/gopath/src/github.com/google/syzkaller# ./bin/syz-execprog -repeat=0 -procs=10 -executor=bin/syz-executor gistfile2.txt
> 2017/03/07 10:35:14 parsed 2 programs
> 2017/03/07 10:35:14 executed 0 programs
> result: failed=false hanged=false err=executor is not serving
>
> 2017/03/07 10:36:14 executed 10 programs
> result: failed=false hanged=false err=executor is not serving
>
> result: failed=false hanged=false err=executor is not serving
>
> result: failed=false hanged=false err=executor is not serving
>
> result: failed=false hanged=false err=executor is not serving
>
> result: failed=false hanged=false err=executor is not serving
>
> result: failed=false hanged=false err=executor is not serving
>
> result: failed=false hanged=false err=executor is not serving
>
> result: failed=false hanged=false err=executor is not serving
>
> result: failed=false hanged=false err=executor is not serving

An old syzkaller may not understand part of syscalls in the program
and silently drop them, you need a new one.

Here is a straightforward conversion of the syzkaller program to C
(with/without namespace sandbox):

https://gist.githubusercontent.com/dvyukov/b6540bed50b7da1dff3d7373ba570c77/raw/fd5f2f3aaa52b70b2bb9f114cf8a3226d8a30960/gistfile1.txt
https://gist.githubusercontent.com/dvyukov/dbd8ec38bcb50df4bdc95210d4247b09/raw/f9cbb5e17cd4ff4a7a7881c97dea7d6cd6dd8bf1/gistfile1.txt

That's also with -procs=10, you can change number of procs in main funciton.

But I wasn't able to reproduce the crash using these programs (neither
the syzkaller program), that's why I did not provide it all initially.