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

[Ameer Hamza <amhamza.mgc@gmail.com>]

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@gmail.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?

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