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

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Message-ID: <20151210090251.GV6356@twins.programming.kicks-ass.net>
Date:	Thu, 10 Dec 2015 10:02:51 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	Dmitry Vyukov <dvyukov@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	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 Wed, Dec 09, 2015 at 07:54:35PM -0800, Alexei Starovoitov wrote:
> Freeing memory is a requirement regardless.
> Even when kernel running with kasan, there must be a way to stop
> stack collection and free that memory.
> You cannot treat kernel as your test program or 'device under test'.

Relax, that is exactly what lockdep does. It cannot dynamically allocate
things because allocators use lock etc..

Its fine to build up state for debug bits, esp. if its bounded, like the
number of unique callchains.
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