Re: [PATCH v1 11/11] perf cs-etm: Smatch: Fix potential NULL pointer dereference

From: Mathieu Poirier <mathieu.poirier@linaro.org>
To: Leo Yan <leo.yan@linaro.org>
Cc: Song Liu <songliubraving@fb.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	linux-kernel@vger.kernel.org, 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,
	Thomas Richter <tmricht@linux.ibm.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	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 11/11] perf cs-etm: Smatch: Fix potential NULL pointer dereference
Date: Tue, 2 Jul 2019 11:03:06 -0600	[thread overview]
Message-ID: <20190702170306.GA17808@xps15> (raw)
In-Reply-To: <20190702103420.27540-12-leo.yan@linaro.org>

Hi Leo,

On Tue, Jul 02, 2019 at 06:34:20PM +0800, Leo Yan wrote:
> Based on the following report from Smatch, fix the potential
> NULL pointer dereference check.
> 
>   tools/perf/util/cs-etm.c:2545
>   cs_etm__process_auxtrace_info() error: we previously assumed
>   'session->itrace_synth_opts' could be null (see line 2541)
> 
> tools/perf/util/cs-etm.c
> 2541         if (session->itrace_synth_opts && session->itrace_synth_opts->set) {
> 2542                 etm->synth_opts = *session->itrace_synth_opts;
> 2543         } else {
> 2544                 itrace_synth_opts__set_default(&etm->synth_opts,
> 2545                                 session->itrace_synth_opts->default_no_sample);
>                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^
> 2546                 etm->synth_opts.callchain = false;
> 2547         }
> 
> To dismiss the potential NULL pointer dereference, this patch validates
> the pointer 'session->itrace_synth_opts' before access its elements.
> 
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
>  tools/perf/util/cs-etm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 0c7776b51045..b79df56eb9df 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -2540,7 +2540,7 @@ int cs_etm__process_auxtrace_info(union perf_event *event,
>  
>  	if (session->itrace_synth_opts && session->itrace_synth_opts->set) {
>  		etm->synth_opts = *session->itrace_synth_opts;
> -	} else {
> +	} else if (session->itrace_synth_opts) {

This will work but we end up checking session->itrace_synth_opts twice.  I
suggest to check it once and then process with the if/else if valid:

        if (session->itrace_synth_opts) {
                if (session->itrace_synth_opts->set) {
                        ...
                } else {
                        ...
                }
        }

Thanks,
Mathieu

>  		itrace_synth_opts__set_default(&etm->synth_opts,
>  				session->itrace_synth_opts->default_no_sample);
>  		etm->synth_opts.callchain = false;
> -- 
> 2.17.1
> 

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