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

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Message-ID: <20170411100531.GC21238@krava>
Date:   Tue, 11 Apr 2017 12:05:31 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Du, Changbin" <changbin.du@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, 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 11, 2017 at 04:25:50PM +0800, Du, Changbin wrote:
> > > (gdb) print fmt.sort_list
> > > $5 = {next = 0x9727d0 <perf_hpp_list+16>, prev = 0x9727d0 <perf_hpp_list+16>}
> > > 
> > > In this case, the fmt is linked in sort_list, but not in list. So crash
> > > at the list_del_init(&fmt->list) of second loop.
> > 
> > so the only place I can see the POISON could get there
> > is in perf_hpp__column_unregister.. can't we just get
> > rid of it like below
> > 
> > jirka
> > 
> > 
> > ---
> > diff --git a/tools/perf/ui/hist.c b/tools/perf/ui/hist.c
> > index 5d632dca672a..7577effbf746 100644
> > --- a/tools/perf/ui/hist.c
> > +++ b/tools/perf/ui/hist.c
> > @@ -529,7 +529,7 @@ void perf_hpp_list__prepend_sort_field(struct perf_hpp_list *list,
> >  
> >  void perf_hpp__column_unregister(struct perf_hpp_fmt *format)
> >  {
> > -	list_del(&format->list);
> > +	list_del_init(&format->list);
> >  }
> >  
> yes, this is an option. But for safety, I sugguest do not rely on list_del_init.
> No rule rather than create one.
> 
> But anyway, both are ok for me. What's your options?

hum, also I dont think we need to touch that bit at all
if we are going to remove it right away.. how about the
change below?

jirka


---
diff --git a/tools/perf/ui/hist.c b/tools/perf/ui/hist.c
index 5d632dca672a..0ee7db43dd7d 100644
--- a/tools/perf/ui/hist.c
+++ b/tools/perf/ui/hist.c
@@ -613,15 +613,15 @@ void perf_hpp__reset_output_field(struct perf_hpp_list *list)
 
 	/* reset output fields */
 	perf_hpp_list__for_each_format_safe(list, fmt, tmp) {
-		list_del_init(&fmt->list);
-		list_del_init(&fmt->sort_list);
+		list_del(&fmt->list);
+		/* Remove the fmt from next loop processing. */
+		list_del(&fmt->sort_list);
 		fmt_free(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);
+		list_del(&fmt->sort_list);
 		fmt_free(fmt);
 	}
 }