Re: KASAN: use-after-free Read in cfusbl_device_notify

[Dae R. Jeong]

On Fri, Jun 24, 2022 at 08:32:31AM +0200, Eric Dumazet wrote:
> On Fri, Jun 24, 2022 at 8:25 AM Dae R. Jeong <threeearcat@xxxxxxxxx> wrote:
> >
> > On Fri, Jun 24, 2022 at 08:15:54AM +0200, Eric Dumazet wrote:
> > > On Fri, Jun 24, 2022 at 8:08 AM Dae R. Jeong <threeearcat@xxxxxxxxx> wrote:
> > > >
> > > > Hello,
> > > >
> > > > We observed a crash "KASAN: use-after-free Read in cfusbl_device_notify" during fuzzing.
> > >
> > > This is a known problem.
> > >
> > > Some drivers do not like NETDEV_UNREGISTER being delivered multiple times.
> > >
> > > Make sure in your fuzzing to have NET_DEV_REFCNT_TRACKER=y
> > >
> > > Thanks.
> >
> > Our config already have CONFIG_NET_DEV_REFCNT_TRACKER=y.
> 
> Are you also setting netdev_unregister_timeout_secs to a smaller value ?
> 
> netdev_unregister_timeout_secs
> ------------------------------
> 
> Unregister network device timeout in seconds.
> This option controls the timeout (in seconds) used to issue a warning while
> waiting for a network device refcount to drop to 0 during device
> unregistration. A lower value may be useful during bisection to detect
> a leaked reference faster. A larger value may be useful to prevent false
> warnings on slow/loaded systems.
> Default value is 10, minimum 1, maximum 3600.

We are using the same config that Syzkaller uses. So its value is 140.

I'm not a network developer so I don't know whether there is a
possibility of a false alarm. Our fuzzer is a research prototype in
development, and I don't want to interrupt you with false alarms...

> > Anyway, this UAF report seems not interesting.
> >
> > Thank you for your quick reply.
> >
> >
> > Best regards,
> > Dae R. Jeong.

Best regards,
Dae R. Jeong.