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

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Date: Tue, 7 May 2024 17:51:10 -0700
From: Ian Rogers <irogers@...gle.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	Oliver Upton <oliver.upton@...ux.dev>, James Clark <james.clark@....com>, 
	Tim Chen <tim.c.chen@...ux.intel.com>, Yicong Yang <yangyicong@...ilicon.com>, 
	K Prateek Nayak <kprateek.nayak@....com>, Yanteng Si <siyanteng@...ngson.cn>, 
	Sun Haiyong <sunhaiyong@...ngson.cn>, Kajol Jain <kjain@...ux.ibm.com>, 
	Ravi Bangoria <ravi.bangoria@....com>, Li Dong <lidong@...o.com>, Paran Lee <p4ranlee@...il.com>, 
	Ben Gainey <ben.gainey@....com>, Andi Kleen <ak@...ux.intel.com>, 
	Athira Rajeev <atrajeev@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v1 1/8] perf ui browser: Don't save pointer to stack memory

On Tue, May 7, 2024 at 2:07 PM Arnaldo Carvalho de Melo <acme@...nel.org> 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@...nel.org> 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