linux-kernel - Re: [PATCH] perf session: check for null pointer before derefernce

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Message-ID: <Yf+z6LmCsyymABcN@kernel.org>
Date:   Sun, 6 Feb 2022 08:41:28 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     James Clark <james.clark@....com>
Cc:     Ameer Hamza <amhamza.mgc@...il.com>,
        German Gomez <german.gomez@....com>, peterz@...radead.org,
        mingo@...hat.com, rickyman7@...il.com,
        alexey.v.bayduraev@...ux.intel.com, adrian.hunter@...el.com,
        leo.yan@...aro.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org
Subject: Re: [PATCH] perf session: check for null pointer before derefernce

Em Tue, Jan 25, 2022 at 09:35:49AM +0000, James Clark escreveu:
> 
> 
> On 24/01/2022 20:29, Ameer Hamza wrote:
> > On Mon, Jan 24, 2022 at 03:30:17PM +0000, James Clark wrote:
> >>
> >>
> >> On 24/01/2022 15:00, Ameer Hamza wrote:
> >>> Move null pointer check before dereferncing the variable
> >>>
> >>> Addresses-Coverity: 1497622 ("Derereference before null check")
> >>>
> >>> Signed-off-by: Ameer Hamza <amhamza.mgc@...il.com>
> >>> ---
> >>>  tools/perf/util/session.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> >>> index f19348dddd55..e1014ab62c10 100644
> >>> --- a/tools/perf/util/session.c
> >>> +++ b/tools/perf/util/session.c
> >>> @@ -1503,11 +1503,11 @@ static int machines__deliver_event(struct machines *machines,
> >>>  			++evlist->stats.nr_unknown_id;
> >>>  			return 0;
> >>>  		}
> >>> -		dump_sample(evsel, event, sample, perf_env__arch(machine->env));
> >>>  		if (machine == NULL) {
> >>>  			++evlist->stats.nr_unprocessable_samples;
> >>>  			return 0;
> >>>  		}
> >>> +		dump_sample(evsel, event, sample, perf_env__arch(machine->env));
> >>>  		return evlist__deliver_sample(evlist, tool, event, sample, evsel, machine);
> >>>  	case PERF_RECORD_MMAP:
> >>>  		return tool->mmap(tool, event, sample, machine);
> >>>
> >>
> >> Hi Ameer,
> >>
> >> This mistake was made recently, but I don't think your change is the desired behavior.
> >>
> >> It should be possible to dump stuff if machine is null. null or an empty string
> >> should be passed to dump_sample(). It looks like some of the printfs still attempt to
> >> show something in this case, although I didn't check them all.
> > 
> > Hi James,
> > 
> > Thank you for your response. I understand your point.
> > 
> > Do you think following changes would be ok?
> 
> Yep looks good. With that change:
> 
> Reviewed-by: James Clark <james.clark@....com>

Thanks, applied.

- Arnaldo

 
> > 
> > diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> > index f19348dddd55..210eeee3dd70 100644
> > --- a/tools/perf/util/session.c
> > +++ b/tools/perf/util/session.c
> > @@ -1503,11 +1503,12 @@ static int machines__deliver_event(struct machines *machines,
> >                         ++evlist->stats.nr_unknown_id;
> >                         return 0;
> >                 }
> > -               dump_sample(evsel, event, sample, perf_env__arch(machine->env));
> >                 if (machine == NULL) {
> >                         ++evlist->stats.nr_unprocessable_samples;
> > +                       dump_sample(evsel, event, sample, perf_env__arch(NULL));
> >                         return 0;
> >                 }
> > +               dump_sample(evsel, event, sample, perf_env__arch(machine->env));
> >                 return evlist__deliver_sample(evlist, tool, event, sample, evsel, machine);
> >         case PERF_RECORD_MMAP:
> >                 return tool->mmap(tool, event, sample, machine);
> > 
> > Thanks,
> > Hamza
> > 

-- 

- Arnaldo