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

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Message-ID: <20170307100026.GD6515@twins.programming.kicks-ass.net>
Date:   Tue, 7 Mar 2017 11:00:26 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        syzkaller <syzkaller@...glegroups.com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: perf: use-after-free in perf_release

On Tue, Mar 07, 2017 at 10:43:32AM +0100, Dmitry Vyukov wrote:

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

That's yucky semantics, better to at least warn on that occasion.

> 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

Thanks!

> 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.

Right, I'll run them while at the same time trying to see what it is
they're doing to find clues.