Re: [PATCH v2] perf: fix double free at function perf_hpp__reset_output_field

[Jiri Olsa <jolsa@redhat.com>]

On Mon, Apr 10, 2017 at 06:21:12PM +0800, Du, Changbin wrote:
> On Mon, Apr 10, 2017 at 10:39:50AM +0200, Jiri Olsa wrote:
> > On Tue, Apr 04, 2017 at 12:19:40PM -0300, Arnaldo Carvalho de Melo wrote:
> > 
> > SNIP
> > 
> > > > ---
> > > >  tools/perf/ui/hist.c | 25 +++++++++++++++----------
> > > >  1 file changed, 15 insertions(+), 10 deletions(-)
> > > > 
> > > > diff --git a/tools/perf/ui/hist.c b/tools/perf/ui/hist.c
> > > > index 5d632dc..f94b301 100644
> > > > --- a/tools/perf/ui/hist.c
> > > > +++ b/tools/perf/ui/hist.c
> > > > @@ -609,20 +609,25 @@ static void fmt_free(struct perf_hpp_fmt *fmt)
> > > >  
> > > >  void perf_hpp__reset_output_field(struct perf_hpp_list *list)
> > > >  {
> > > > -	struct perf_hpp_fmt *fmt, *tmp;
> > > > +	struct perf_hpp_fmt *field_fmt, *sort_fmt, *tmp1, *tmp2;
> > > >  
> > > >  	/* reset output fields */
> > > > -	perf_hpp_list__for_each_format_safe(list, fmt, tmp) {
> > > > -		list_del_init(&fmt->list);
> > > > -		list_del_init(&fmt->sort_list);
> > > > -		fmt_free(fmt);
> > > > +	perf_hpp_list__for_each_format_safe(list, field_fmt, tmp1) {
> > > > +		list_del_init(&field_fmt->list);
> > > > +		/* reset sort keys */
> > > > +		perf_hpp_list__for_each_sort_list_safe(list, sort_fmt, tmp2) {
> > > > +			if (field_fmt == sort_fmt) {
> > > > +				list_del_init(&field_fmt->sort_list);
> > > > +				break;
> > > > +			}
> > > > +		}
> > 
> > I agree with Namhyung in here.. seems like the only thing you
> > added is to check if the field_fmt was also linked in as a sort
> > entry before you call list_del_init on it
> >
> This is correct.
> 
> > which I think should be also done with list_empty function, but
> > more importantly I dont see a reason for that.. list_del_init
> > call should be fine on empty list
> > 
> You didn't catch the problem here. The problem is double free a fmt.
> For exampe, fmt A is linked to both list. Then it will be first free
> by the first iteration over list, then it will be freed again at the
> second iteration over sort_list. This must cause application crash.

the original code takes it out of both lists,
so the next itaration won't go over that entry

jirka