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

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Date:   Tue, 11 Apr 2017 09:35:45 +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 11:06:14AM +0800, Du, Changbin wrote:

SNIP

> > the original code takes it out of both lists,
> > so the next itaration won't go over that entry
> >
> oh, my bad, my desc is wrong. I replayed the crash. The problem is
> list_del_init a unlinked entry.
> 
> perf: Segmentation fault
> -------- backtrace --------
> ./perf[0x57394b]
> /lib/x86_64-linux-gnu/libc.so.6(+0x354b0)[0x7fb8da3034b0]
> ./perf(perf_hpp__reset_output_field+0xb7)[0x55dfe7]
> ./perf(hists__sort_by_fields+0x3d7)[0x509777]
> ./perf[0x5704c1]
> ./perf(perf_evlist__tui_browse_hists+0x2e5)[0x5723e5]
> ./perf(cmd_report+0x1a9b)[0x43b4fb]
> ./perf[0x494731]
> ./perf(main+0x704)[0x426304]
> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7fb8da2ee830]
> ./perf(_start+0x29)[0x4263f9]
> [0x0]
> 
> (gdb) print fmt.list
> $4 = {next = 0x100, prev = 0x200}    // LIST_POISON
> (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);
 }
 
 void perf_hpp__cancel_cumulate(void)