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

From: Leo Yan <leo.yan@linaro.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Song Liu <songliubraving@fb.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Jin Yao <yao.jin@linux.intel.com>, Jiri Olsa <jolsa@redhat.com>,
	Andi Kleen <ak@linux.intel.com>,
	Eric Saint-Etienne <eric.saint.etienne@oracle.com>,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	Ingo Molnar <mingo@redhat.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexios Zavras <alexios.zavras@intel.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Namhyung Kim <namhyung@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Thomas Richter <tmricht@linux.ibm.com>,
	linux-kernel@vger.kernel.org,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	Changbin Du <changbin.du@intel.com>,
	Alexey Budankov <alexey.budankov@linux.intel.com>
Subject: Re: [PATCH v1 10/11] perf intel-pt: Smatch: Fix potential NULL pointer dereference
Date: Wed, 3 Jul 2019 16:16:57 +0800	[thread overview]
Message-ID: <20190703081657.GD6852@leoy-ThinkPad-X240s> (raw)
In-Reply-To: <b65cf4c6-3484-85c8-d191-35021ed6ed3e@intel.com>

On Wed, Jul 03, 2019 at 08:19:19AM +0300, Adrian Hunter wrote:
> 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.

Yes.

I also checked the another case for 'perf inject', just as you said,
it sets both inject->tool.auxtrace_info and session->itrace_synth_opts
if we use 'itrace' option.  So it's safe to remove the NULL test for
session->itrace_synth_opts.

Will follow your suggestion for new patches.  Thanks a lot for
confirmation and suggestions.

Thanks,
Leo Yan

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