linux-kernel - Re: [PATCH] perf evsel: fix NULL pointer deference when evsel->counts is NULL

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Date:	Wed, 23 Jan 2013 23:26:20 +0000
From:	Colin Ian King <colin.king@...onical.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf evsel: fix NULL pointer deference when evsel->counts
 is NULL

On 23/01/13 22:02, Arnaldo Carvalho de Melo wrote:
> Em Mon, Jan 21, 2013 at 01:53:21PM +0900, Namhyung Kim escreveu:
>> On Sat, 19 Jan 2013 16:36:54 +0000, Colin King wrote:
>>> From: Colin Ian King <colin.king@...onical.com>
>
>>> __perf_evsel__read_on_cpu() only bails out with -ENOMEM if
>>> evsel->counts is NULL and perf_evsel__alloc_counts() has returned
>>> an error.  If perf_evsel__alloc_counts() does not return an error
>>> we get an NULL pointer deference on evsel->counts->cpu[cpu]
>>> if evsel->counts is NULL.
>
>> perf_evsel__alloc_counts() should allocate evsel->counts when it sees
>> evsel->counts is NULL and return negative error code if the allocation
>> fails.
>
>> So I don't see any problem in current code.  With your code, it won't
>> try to allocate if ->counts is NULL but overwrite existing ->counts?
>
> Right, the patch introduces a problem in code that works perfectly :-)
>
> - Arnaldo
>
Apologies for the noise.

Colin
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