linux-kernel - Re: [PATCH v1 10/11] perf intel-pt: Smatch: Fix potential NULL pointer dereference

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Message-ID: <b65cf4c6-3484-85c8-d191-35021ed6ed3e@intel.com>
Date:   Wed, 3 Jul 2019 08:19:19 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Andi Kleen <ak@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Davidlohr Bueso <dave@...olabs.net>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Song Liu <songliubraving@...com>,
        Alexios Zavras <alexios.zavras@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Changbin Du <changbin.du@...el.com>,
        Eric Saint-Etienne <eric.saint.etienne@...cle.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1 10/11] perf intel-pt: Smatch: Fix potential NULL
 pointer dereference

On 3/07/19 4:35 AM, Leo Yan wrote:
> Hi Adrian,
> 
> On Tue, Jul 02, 2019 at 02:07:40PM +0300, Adrian Hunter wrote:
>> On 2/07/19 1:34 PM, Leo Yan wrote:
>>> Based on the following report from Smatch, fix the potential
>>> NULL pointer dereference check.
>>
>> It never is NULL.  Remove the NULL test if you want:
>>
>> -	if (session->itrace_synth_opts && session->itrace_synth_opts->set) {
>> +	if (session->itrace_synth_opts->set) {
>>
>> But blindly making changes like below is questionable.
> 
> Thanks for suggestions.
> 
> I checked report and script commands, as you said, both command will
> always set session->itrace_synth_opts.  For these two commands, we can
> safely remove the NULL test.
> 
> Because perf tool contains many sub commands, so I don't have much
> confidence it's very safe to remove the NULL test for all cases; e.g.
> there have cases which will process aux trace buffer but without
> itrace options; for this case, session->itrace_synth_opts might be NULL.
> 
> For either way (remove NULL test or keep NULL test), I don't want to
> introduce regression and extra efforts by my patch.  So want to double
> confirm with you for this :)

Yes, intel_pt_process_auxtrace_info() only gets called if a tool sets up the
tools->auxtrace_info() callback.  The tools that do that also set
session->itrace_synth_opts.