Re: [PATCH v1 1/8] perf ui browser: Don't save pointer to stack memory

[Ian Rogers]

On Tue, May 7, 2024 at 2:07 PM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
>
> On Tue, May 07, 2024 at 06:04:43PM -0300, Arnaldo Carvalho de Melo wrote:
> > On Tue, May 07, 2024 at 01:48:28PM -0700, Ian Rogers wrote:
> > > On Tue, May 7, 2024 at 1:22 PM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
> > > >
> > > > On Tue, May 07, 2024 at 05:20:59PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > > On Tue, May 07, 2024 at 11:35:38AM -0700, Ian Rogers wrote:
> > > > > > ui_browser__show is capturing the input title that is stack allocated
> > > > > > memory in hist_browser__run. Avoid a use after return by strdup-ing
> > > > > > the string.
> > > > >
> > > > > But everything happens in that context, i.e. hist_brower__run() will
> > > > > call ui_browser__ methods and then exit.
> > > > >
> > > > > We end up having browser->title pointing to returned stack memory
> > > > > (invalid) but there will be no references to it, no?
> > > > >
> > > > > If we return to hist_browser__run() we then call ui_browser__show
> > > > > passing a new title, for "live" stack memory, rinse repeat. Or have you
> > > > > noticed an actual use-after-"free"?
> > > >
> > > > And I'll take the patch, I'm just trying to figure it out if it fixed a
> > > > real bug or if it just makes the code more future proof, i.e. to avoid
> > > > us adding code that actually uses invalid stack memory.
> > >
> > > My command line using tui is:
> > > $ sudo bash -c 'rm /tmp/asan.log*; export
> > > ASAN_OPTIONS="log_path=/tmp/asan.log"; /tmp/perf/perf mem record -a
> > > sleep 1; /tmp/perf/perf mem report'
> > > I then go to the perf annotate view and quit. This triggers the asan
> > > error (from the log file):
> > > ```
> >
> > Thanks, it is indeed a bug, I'll keep that Fixes tag, people interested
> > in the full details can hopefully find this message going from the Link:
> > tag.
>
> Nah, I added your explanation to the cset log message.


Okay, I found I needed this to avoid a segv introduced by this patch:
```
diff --git a/tools/perf/ui/browser.c b/tools/perf/ui/browser.c
index c4cdf2ea69b7..19503e838738 100644
--- a/tools/perf/ui/browser.c
+++ b/tools/perf/ui/browser.c
@@ -203,7 +203,7 @@ void ui_browser__refresh_dimensions(struct
ui_browser *browser)
void ui_browser__handle_resize(struct ui_browser *browser)
{
       ui__refresh_dimensions(false);
-       ui_browser__show(browser, browser->title, ui_helpline__current);
+       ui_browser__show(browser, browser->title ?: "", ui_helpline__current);
       ui_browser__refresh(browser);
}
```
I also found a use-after-free issue with patch 5. I'll send a v2.

Thanks,
Ian

> Thanks,
>
> - Arnaldo