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

Leo Yan
2019-07-03T08:23:30Z

Hi Mathieu,

On Tue, Jul 02, 2019 at 11:03:06AM -0600, Mathieu Poirier wrote:
> 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 for reviewing.

As discussed with Adrian in another email for intel-pt, it's safe to
remove NULL checking for session->itrace_synth_opts after I reviewed the
code for report/script/inject. So I'm planning to apply the same change
for cs-etm code.

If you have concern for this, please let me know.

Thanks,
Leo Yan

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