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

[Arnaldo Carvalho de Melo]

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.

- Arnaldo
 
> - Arnaldo
>  
> > Fixes: 05e8b0804ec4 ("perf ui browser: Stop using 'self'")
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > ---
> >  tools/perf/ui/browser.c | 4 +++-
> >  tools/perf/ui/browser.h | 2 +-
> >  2 files changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/perf/ui/browser.c b/tools/perf/ui/browser.c
> > index 603d11283cbd..c4cdf2ea69b7 100644
> > --- a/tools/perf/ui/browser.c
> > +++ b/tools/perf/ui/browser.c
> > @@ -287,7 +287,8 @@ int ui_browser__show(struct ui_browser *browser, const char *title,
> >  	mutex_lock(&ui__lock);
> >  	__ui_browser__show_title(browser, title);
> >  
> > -	browser->title = title;
> > +	free(browser->title);
> > +	browser->title = strdup(title);
> >  	zfree(&browser->helpline);
> >  
> >  	va_start(ap, helpline);
> > @@ -304,6 +305,7 @@ void ui_browser__hide(struct ui_browser *browser)
> >  	mutex_lock(&ui__lock);
> >  	ui_helpline__pop();
> >  	zfree(&browser->helpline);
> > +	zfree(&browser->title);
> >  	mutex_unlock(&ui__lock);
> >  }
> >  
> > diff --git a/tools/perf/ui/browser.h b/tools/perf/ui/browser.h
> > index 510ce4554050..6e98d5f8f71c 100644
> > --- a/tools/perf/ui/browser.h
> > +++ b/tools/perf/ui/browser.h
> > @@ -21,7 +21,7 @@ struct ui_browser {
> >  	u8	      extra_title_lines;
> >  	int	      current_color;
> >  	void	      *priv;
> > -	const char    *title;
> > +	char	      *title;
> >  	char	      *helpline;
> >  	const char    *no_samples_msg;
> >  	void 	      (*refresh_dimensions)(struct ui_browser *browser);
> > -- 
> > 2.45.0.rc1.225.g2a3ae87e7f-goog