On Wed, Dec 09, 2015 at 02:05:17PM -0800, Kees Cook wrote:
> On Wed, Dec 9, 2015 at 1:48 PM, Brian Norris
> <computersforpeace@xxxxxxxxx> wrote:
> > I was also thinking, since use-after-free isn't necessarily immediately
> > obvious (this worked fine in my testing), that maybe we could poison the
> > buffer before kfree()'ing? Like:
> >
> > name = ...;
> > len = strlen(name);
> >
> > ...
> >
> > rc = request_firmware_nowait(...);
> > if (rc) {
> > pr_info("...");
> > kfree(name);
> > goto out;
> > }
> > /*
> > * Clear out the name, to test for race conditions with the
> > * async request
> > */
> > memset(name, 0, len);
> > kfree(name);
>
> Hrm, well, I'm not against it, but I think running under KASan is
> probably the right way to find these things. But, might as well, just
> to notice any regressions.
Fair enough. The memset probably isn't that useful.
BTW, one reason I didn't notice my use-after-free is that the "use" was
under an error path that I didn't exercise. I need to remember to turn
my brain back on.
Brian
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