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

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Date:   Tue, 4 Apr 2017 12:51:03 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, changbin.du@...el.com,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] perf: fix double free at function
 perf_hpp__reset_output_field

Em Wed, Apr 05, 2017 at 12:34:59AM +0900, Namhyung Kim escreveu:
> Hi Arnaldo,
> 
> On Wed, Apr 5, 2017 at 12:19 AM, Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> > Em Mon, Mar 27, 2017 at 02:22:55PM +0800, changbin.du@...el.com escreveu:
> >> From: Changbin Du <changbin.du@...el.com>
> >>
> >> Some perf_hpp_fmt both registered at field and sort list. For such
> >> instance, we only can free it when removed from the both lists. This
> >> function currently only used by self-test code, but still should fix
> >> it.
> >
> > Looks sane, applying,
> >
> > Jiri, Namhyung, please holler (or ack) if needed,
> 
> Did you actually see the double free problem?  AFAICS the old code

I assumed that he had seen it, in some self-test code, Changbin, can you
please show command output or further describe when this patch would be
necessary?

- Arnaldo

> removed a fmt from both list before free it.  In the first loop, fmt that
> was linked to both output list and sort list will be remove.  And the
> second loop frees fmt that was linked only to the sort list (IOW, it
> frees fmt that was not freed in the first loop).
> 
> Thanks,
> Namhyung
> 
> 
> >
> > - Arnaldo
> >
> >> Signed-off-by: Changbin Du <changbin.du@...el.com>
> >> ---
> >> v2: removed redundant Signed-off.
> >>
> >> ---
> >>  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;
> >> +                     }
> >> +             }
> >> +             fmt_free(field_fmt);
> >>       }
> >>
> >> -     /* reset sort keys */
> >> -     perf_hpp_list__for_each_sort_list_safe(list, fmt, tmp) {
> >> -             list_del_init(&fmt->list);
> >> -             list_del_init(&fmt->sort_list);
> >> -             fmt_free(fmt);
> >> +     /* reset remaining sort keys */
> >> +     perf_hpp_list__for_each_sort_list_safe(list, sort_fmt, tmp1) {
> >> +             list_del_init(&sort_fmt->sort_list);
> >> +             fmt_free(sort_fmt);
> >>       }
> >>  }
> >>
> >> --
> >> 2.7.4