Re: [PATCHv5] perf tool: fix dereferencing NULL al->maps

[Namhyung Kim]

Hello,

On Tue, Jul 23, 2024 at 6:01 PM Casey Chen <cachen@xxxxxxxxxxxxxxx> wrote:
>
> Ian / Namhyung,
>
> Could you take a look at the latest diff PATCHv5 ?
>
> Thanks,
> Casey
>
> On Mon, Jul 22, 2024 at 2:15 PM Casey Chen <cachen@xxxxxxxxxxxxxxx> wrote:
> >
> > With 0dd5041c9a0e ("perf addr_location: Add init/exit/copy functions"),
> > when cpumode is 3 (macro PERF_RECORD_MISC_HYPERVISOR),
> > thread__find_map() could return with al->maps being NULL.
> >
> > The path below could add a callchain_cursor_node with NULL ms.maps.
> >
> > add_callchain_ip()
> >   thread__find_symbol(.., &al)
> >     thread__find_map(.., &al)   // al->maps becomes NULL
> >   ms.maps = maps__get(al.maps)
> >   callchain_cursor_append(..., &ms, ...)
> >     node->ms.maps = maps__get(ms->maps)
> >
> > Then the path below would dereference NULL maps and get segfault.
> >
> > fill_callchain_info()
> >   maps__machine(node->ms.maps);
> >
> > Fix it by checking if maps is NULL in fill_callchain_info().
> >
> > Signed-off-by: Casey Chen <cachen@xxxxxxxxxxxxxxx>
> > Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung


> > ---
> >  tools/perf/util/callchain.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> > index 1730b852a947..6d075648d2cc 100644
> > --- a/tools/perf/util/callchain.c
> > +++ b/tools/perf/util/callchain.c
> > @@ -1141,7 +1141,7 @@ int hist_entry__append_callchain(struct hist_entry *he, struct perf_sample *samp
> >  int fill_callchain_info(struct addr_location *al, struct callchain_cursor_node *node,
> >                         bool hide_unresolved)
> >  {
> > -       struct machine *machine = maps__machine(node->ms.maps);
> > +       struct machine *machine = node->ms.maps ? maps__machine(node->ms.maps) : NULL;
> >
> >         maps__put(al->maps);
> >         al->maps = maps__get(node->ms.maps);
> > --
> > 2.45.2
> >