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

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Date:	Thu, 10 Dec 2015 09:03:06 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 Thu, Dec 10, 2015 at 10:02:51AM +0100, Peter Zijlstra wrote:
> 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.

except the code in question is doing unbounded alloc_pages()

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