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[45.33.10.79]) by smtp.gmail.com with ESMTPSA id n26sm344887otq.10.2019.07.02.18.35.57 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 02 Jul 2019 18:36:03 -0700 (PDT) Date: Wed, 3 Jul 2019 09:35:54 +0800 From: Leo Yan To: Adrian Hunter Cc: Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Mathieu Poirier , Suzuki K Poulose , Andi Kleen , "David S. Miller" , Davidlohr Bueso , Rasmus Villemoes , Jin Yao , Song Liu , Alexios Zavras , Thomas Gleixner , Changbin Du , Eric Saint-Etienne , Konstantin Khlebnikov , Thomas Richter , Alexey Budankov , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v1 10/11] perf intel-pt: Smatch: Fix potential NULL pointer dereference Message-ID: <20190703013553.GB6852@leoy-ThinkPad-X240s> References: <20190702103420.27540-1-leo.yan@linaro.org> <20190702103420.27540-11-leo.yan@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 :) Thanks, Leo Yan > > tools/perf/util/intel-pt.c:3200 > > intel_pt_process_auxtrace_info() error: we previously assumed > > 'session->itrace_synth_opts' could be null (see line 3196) > > > > tools/perf/util/intel-pt.c:3206 > > intel_pt_process_auxtrace_info() warn: variable dereferenced before > > check 'session->itrace_synth_opts' (see line 3200) > > > > tools/perf/util/intel-pt.c > > 3196 if (session->itrace_synth_opts && session->itrace_synth_opts->set) { > > 3197 pt->synth_opts = *session->itrace_synth_opts; > > 3198 } else { > > 3199 itrace_synth_opts__set_default(&pt->synth_opts, > > 3200 session->itrace_synth_opts->default_no_sample); > > ^^^^^^^^^^^^^^^^^^^^^^^^^^ > > 3201 if (!session->itrace_synth_opts->default_no_sample && > > 3202 !session->itrace_synth_opts->inject) { > > 3203 pt->synth_opts.branches = false; > > 3204 pt->synth_opts.callchain = true; > > 3205 } > > 3206 if (session->itrace_synth_opts) > > ^^^^^^^^^^^^^^^^^^^^^^^^^^ > > 3207 pt->synth_opts.thread_stack = > > 3208 session->itrace_synth_opts->thread_stack; > > 3209 } > > > > 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 > > --- > > tools/perf/util/intel-pt.c | 5 ++--- > > 1 file changed, 2 insertions(+), 3 deletions(-) > > > > diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c > > index 550db6e77968..88b567bdf1f9 100644 > > --- a/tools/perf/util/intel-pt.c > > +++ b/tools/perf/util/intel-pt.c > > @@ -3195,7 +3195,7 @@ int intel_pt_process_auxtrace_info(union perf_event *event, > > > > if (session->itrace_synth_opts && session->itrace_synth_opts->set) { > > pt->synth_opts = *session->itrace_synth_opts; > > - } else { > > + } else if (session->itrace_synth_opts) { > > itrace_synth_opts__set_default(&pt->synth_opts, > > session->itrace_synth_opts->default_no_sample); > > if (!session->itrace_synth_opts->default_no_sample && > > @@ -3203,8 +3203,7 @@ int intel_pt_process_auxtrace_info(union perf_event *event, > > pt->synth_opts.branches = false; > > pt->synth_opts.callchain = true; > > } > > - if (session->itrace_synth_opts) > > - pt->synth_opts.thread_stack = > > + pt->synth_opts.thread_stack = > > session->itrace_synth_opts->thread_stack; > > } > > > > >