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

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Date:	Tue, 8 Dec 2015 19:57:38 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Dmitry Vyukov <dvyukov@...gle.com>, 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


* Peter Zijlstra <peterz@...radead.org> 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. 
> 
> Typical that :/
> 
> > 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.
> 
> So I'm still going over the code, but meanwhile I tried reproducing this
> using the perf_fuzzer and some debug code, but no luck with that.
> 
> Since you seem to be able to reproduce, could you do a run with the
> below patch in to see if it tickles something?

Btw., could we add more redundancy / debug code to the refcounting code? It seems 
to be a frequent source of very hard to find/fix races/bugs - so it should be ripe 
for some extra debug infrastructure ...

Thanks,


	Ingo
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