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

Adrian Hunter
2019-07-02T11:43:51Z

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.

>
> 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 <leo.yan@linaro.org>
> ---
> 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;
> }
>
>