Re: [syzbot] [wireguard?] KASAN: slab-use-after-free Write in enqueue_timer

[Eric Dumazet <edumazet@google.com>]

On Tue, May 23, 2023 at 6:05 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Tue, 23 May 2023 17:46:20 +0200 Jason A. Donenfeld wrote:
> > > Freed by task 41:
> > >  __kmem_cache_free+0x264/0x3c0 mm/slub.c:3799
> > >  device_release+0x95/0x1c0
> > >  kobject_cleanup lib/kobject.c:683 [inline]
> > >  kobject_release lib/kobject.c:714 [inline]
> > >  kref_put include/linux/kref.h:65 [inline]
> > >  kobject_put+0x228/0x470 lib/kobject.c:731
> > >  netdev_run_todo+0xe5a/0xf50 net/core/dev.c:10400
> >
> > So that means the memory in question is actually the one that's
> > allocated and freed by the networking stack. Specifically, dev.c:10626
> > is allocating a struct net_device with a trailing struct wg_device (its
> > priv_data). However, wg_device does not have any struct timer_lists in
> > it, and I don't see how net_device's watchdog_timer would be related to
> > the stacktrace which is clearly operating over a wg_peer timer.
> >
> > So what on earth is going on here?
>
> Your timer had the pleasure of getting queued _after_ a dead watchdog
> timer, no? IOW it tries to update the ->next pointer of a queued
> watchdog timer. We should probably do:
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 374d38fb8b9d..f3ed20ebcf5a 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10389,6 +10389,8 @@ void netdev_run_todo(void)
>                 WARN_ON(rcu_access_pointer(dev->ip_ptr));
>                 WARN_ON(rcu_access_pointer(dev->ip6_ptr));
>
> +               WARN_ON(timer_shutdown_sync(&dev->watchdog_timer));
> +
>                 if (dev->priv_destructor)
>                         dev->priv_destructor(dev);
>                 if (dev->needs_free_netdev)
>
> to catch how that watchdog_timer is getting queued. Would that make
> sense, Eric?

Would this case be catched at the time the device is freed ?

(CONFIG_DEBUG_OBJECTS_FREE=y or something)