Re: [PATCH v2 2/3] perf hists browser: Add NULL pointer check to prevent crash

[Namhyung Kim <namhyung@kernel.org>]

On Thu, Dec 03, 2015 at 03:08:14AM +0000, Wang Nan wrote:
> Before this patch we can trigger a segfault by following steps:
> 
>  Step 0: Use 'perf record' to generate a perf.data without callchain
> 
>  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)
> 
>  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@huawei.com>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>

Acked-by: Namhyung Kim <namhyung@kernel.org>

A nitpick below..


> ---
>  tools/perf/ui/browsers/hists.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tools/perf/ui/browsers/hists.c b/tools/perf/ui/browsers/hists.c
> index 601a585..7447515 100644
> --- a/tools/perf/ui/browsers/hists.c
> +++ b/tools/perf/ui/browsers/hists.c
> @@ -1297,6 +1297,9 @@ static void ui_browser__hists_seek(struct ui_browser *browser,
>  	 * and stop when we printed enough lines to fill the screen.
>  	 */
>  do_offset:
> +
> +	if (!nd)
> +		return;

Just a style comment, not serious.  I prefer the blank line is
under the if statement like below..

 do_offset:
+	if (!nd)
+		return;
+

Thanks,
Namhyung


>  	if (offset > 0) {
>  		do {
>  			h = rb_entry(nd, struct hist_entry, rb_node);
> -- 
> 1.8.3.4
>