Re: [PATCH] perf trace: Fix potential USE_AFTER_FREE problem

[YU Bo]

Hi,
On Thu, Feb 14, 2019 at 09:34:11AM +0100, Jiri Olsa wrote:
> On Thu, Feb 14, 2019 at 12:23:56AM -0500, Bo YU wrote:
> > From: Bo Yu <tsu.yubo@xxxxxxxxx>
> >
> > There is a freed pointer "evsel", so fix it.
> >
> > Detected by CoverityScan, CID#1442595("Memory-illegalaccesses
> > (USE_AFTER_FREE)")
> > Fixes: 6ab3bc240ade4("perf trace: Support multiple "vfs_getname" probes")
> >
> > Signed-off-by: Bo Yu <tsu.yubo@xxxxxxxxx>
> > ---
> >  tools/perf/builtin-trace.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> > index b36061cd1ab8..4036b20a1067 100644
> > --- a/tools/perf/builtin-trace.c
> > +++ b/tools/perf/builtin-trace.c
> > @@ -2515,7 +2515,7 @@ static size_t trace__fprintf_thread_summary(struct trace *trace, FILE *fp);
> >  static bool perf_evlist__add_vfs_getname(struct perf_evlist *evlist)
> >  {
> >  	bool found = false;
> > -	struct perf_evsel *evsel, *tmp;
> > +	struct perf_evsel *evsel = NULL, *tmp;
>
> hum, I can't see how this change could matter,
> could you pelase explain
First, this is a warning reported by CoverityScan,but in fact i do not how
to answer your question :(.
Second, if i remember right, temporary element of list_for_each_entry_safe
should be initialized with NULL otherwise it will complain via gcc.
Please correct me :)
Thanks,
> jirka
>
> >  	struct parse_events_error err = { .idx = 0, };
> >  	int ret = parse_events(evlist, "probe:vfs_getname*", &err);
> >
> > --
> > 2.11.0