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

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Message-ID: <20130123220200.GE6687@ghostprotocols.net>
Date:	Wed, 23 Jan 2013 19:02:00 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Colin King <colin.king@...onical.com>,
	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

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
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