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

[Namhyung Kim <namhyung@kernel.org>]

On Wed, Jul 24, 2024 at 11:51:44AM -0700, Casey Chen wrote:
> On Wed, Jul 24, 2024 at 9:19 AM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > Hello,
> >
> > On Tue, Jul 23, 2024 at 6:01 PM Casey Chen <cachen@purestorage.com> 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@purestorage.com> 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@purestorage.com>
> > > > Reviewed-by: Ian Rogers <irogers@google.com>
> >
> > Acked-by: Namhyung Kim <namhyung@kernel.org>
> >
> > 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
> > > >
> 
> Thanks Namhyung.
> I have another question. When will this patch get merged into master
> branch or 6.6 release line ? Our benchmark systems depend on this fix
> to do performance analysis. Currently, both our kernel and perf are on
> 6.6.9 and they build separately. We want to update perf hash without
> patching it locally.

I'll route it to v6.11 through perf-tools tree.  Hopefully it'd get
backported to stable kernels later.

Thanks,
Namhyung