linux-kernel - Re: NULL ptr deref in perf/filter

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Date:	Thu, 4 Aug 2016 17:17:33 +0200
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	David Carrillo-Cisneros <davidcc@...gle.com>,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Kan Liang <kan.liang@...el.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: Re: NULL ptr deref in perf/filter_match

On 4 August 2016 at 14:37, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Jul 29, 2016 at 11:41:11PM +0200, Vegard Nossum wrote:
>
>> Digging a bit deeper into this, it seems the event itself is getting
>> created by perf_event_open() and it gets added to the pmu_event_list
>> through:
>>
>> perf_event_open()
>>  - perf_event_alloc()
>>     - account_event()
>>        - account_pmu_sb_event()
>>           - attach_sb_event()
>>
[...]
>> So I guess the question is... should the event be attached (= put on
>> the list) before ->ctx gets set? Or should the cgroup code check for a
>> NULL ->ctx?
>
> Does this fix it? Ordering is a bit of a mess, adding the events to the
> list _after_ they've been installed has the risk of missing things I
> think, nor does that result in particularly nice code.
>
> Then again, this isn't pretty either.

Patch seems to fix it here, thanks! Feel free to add:

Tested-by: Vegard Nossum <vegard.nossum@...cle.com>


Vegard