Re: [PATCH 1/2] perf hists browser: Add NULL pointer check to prevent crash

[Wangnan (F)]

On 2015/12/2 23:59, Namhyung Kim wrote:
> On Wed, Dec 02, 2015 at 12:51:32PM +0000, Wang Nan wrote:
> > Before this patch we can trigger a segfault by following steps:
> >
> >   Step 1: perf report
> >
> >   Step 2: Use UP/DOWN to select an entry, don't press 'ENTER'
> >
> >   Step 3: Use '/' to filter symbols, use a filter which returns
> >           empty result
> >
> >   Step 4: Press 'ENTER' (notice here that the old selection is still
> > 		        there. This is another problem)
> I guess your data file doesn't contain callchains.  Otherwise 'ENTER'
> key will toggle it and not show context menu.


Yes. With callchain information, this step should be replaced
by:

Toggle an entry and select a leaf entry which can be annotated
with UP and DOWN, don't press 'ENTER'.

I get similar result.

>   We now support 'm' key
> to show context menu in any case.
>
>
> >   Step 5: Press 'ENTER' to annotate that symbol
> >
> >   Step 6: Press 'LEFT' to go out.
> >
> >   Result: segfault:
> >
> >   perf: Segmentation fault
> >   -------- backtrace --------
> >   /home/wangnan/perf[0x53e568]
> >   /lib64/libc.so.6(+0x3545f)[0x7fba75d3245f]
> >   /home/wangnan/perf[0x537516]
> >   /home/wangnan/perf[0x533fef]
> >   /home/wangnan/perf[0x53b347]
> >   /home/wangnan/perf(perf_evlist__tui_browse_hists+0x96)[0x53d206]
> >   /home/wangnan/perf(cmd_report+0x1b9f)[0x442c7f]
> >   /home/wangnan/perf[0x47efa2]
> >   /home/wangnan/perf(main+0x5f5)[0x432fa5]
> >   /lib64/libc.so.6(__libc_start_main+0xf4)[0x7fba75d1ebd4]
> >   /home/wangnan/perf[0x4330d4]
> >
> > This is because in this case 'nd' could be NULL in
> > ui_browser__hists_seek(), but that function never check it.
> >
> > This patch adds checker for potential NULL pointer in that function.
> > After this patch the above steps won't segfault again.
> >
> > Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> > Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> > ---
> >   tools/perf/ui/browsers/hists.c | 8 ++++++--
> >   1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/perf/ui/browsers/hists.c b/tools/perf/ui/browsers/hists.c
> > index 33da341..9458da8 100644
> > --- a/tools/perf/ui/browsers/hists.c
> > +++ b/tools/perf/ui/browsers/hists.c
> > @@ -1280,8 +1280,10 @@ static void ui_browser__hists_seek(struct ui_browser *browser,
> >   	 * Moves not relative to the first visible entry invalidates its
> >   	 * row_offset:
> >   	 */
> > -	h = rb_entry(browser->top, struct hist_entry, rb_node);
> > -	h->row_offset = 0;
> > +	if (browser->top) {
> > +		h = rb_entry(browser->top, struct hist_entry, rb_node);
> > +		h->row_offset = 0;
> > +	}
> Did you have a problem with this code?  It seems that
> ui_browser__hists_init_top() ensures browser->top is initialized.

No. Add it for safty because I see in following code that browser->top
can be NULL.

Will be removed in next version.

Thank you.


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