linux-kernel - Re: [PATCH v2] perf: fix double free at function perf_hpp__reset_output

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Date:   Mon, 10 Apr 2017 10:39:50 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        changbin.du@...el.com, peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] perf: fix double free at function
 perf_hpp__reset_output_field

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

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

please describe the issue in more details, perhaps we'ew missing
something

jirka