Re: [PATCH] libperf: xyarray: Add bounds checks to xyarray__entry()

[Rob Herring]

On Wed, Apr 14, 2021 at 3:25 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Thu, Apr 15, 2021 at 4:58 AM Rob Herring <robh@xxxxxxxxxx> wrote:
> >
> > xyarray__entry() is missing any bounds checking yet often the x and y
> > parameters come from external callers. Add bounds checks and an
> > unchecked __xyarray__entry().
> >
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> > Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
> > ---
> >  tools/lib/perf/include/internal/xyarray.h | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/lib/perf/include/internal/xyarray.h b/tools/lib/perf/include/internal/xyarray.h
> > index 51e35d6c8ec4..f0896c00b494 100644
> > --- a/tools/lib/perf/include/internal/xyarray.h
> > +++ b/tools/lib/perf/include/internal/xyarray.h
> > @@ -18,11 +18,18 @@ struct xyarray *xyarray__new(int xlen, int ylen, size_t entry_size);
> >  void xyarray__delete(struct xyarray *xy);
> >  void xyarray__reset(struct xyarray *xy);
> >
> > -static inline void *xyarray__entry(struct xyarray *xy, int x, int y)
> > +static inline void *__xyarray__entry(struct xyarray *xy, int x, int y)
> >  {
> >         return &xy->contents[x * xy->row_size + y * xy->entry_size];
> >  }
> >
> > +static inline void *xyarray__entry(struct xyarray *xy, int x, int y)
> > +{
> > +       if (x >= xy->max_x || y >= xy->max_y)
> > +               return NULL;
>
> Maybe better to check negatives as well.

max_x and max_y are size_t and unsigned, so x and y will be promoted
to unsigned and the check will still work.

It's probably better to change the args to size_t though. And perhaps
on xyarray__new(), xyarray__max_y(), and xyarray__max_x() as well.

Rob