Re: KASAN: invalid-access Write in enqueue_timer

Dmitry Vyukov
2021-02-16T18:16:17Z

On Tue, Feb 16, 2021 at 7:01 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Tue, Feb 16, 2021 at 06:50:20PM +0100, Jason A. Donenfeld wrote:
> > On Tue, Feb 16, 2021 at 6:46 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> > > On Tue, Feb 16, 2021 at 6:28 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > > > > hlist_add_head include/linux/list.h:883 [inline]
> > > > > enqueue_timer+0x18/0xc0 kernel/time/timer.c:581
> > > > > mod_timer+0x14/0x20 kernel/time/timer.c:1106
> > > > > mod_peer_timer drivers/net/wireguard/timers.c:37 [inline]
> > > > > wg_timers_any_authenticated_packet_traversal+0x68/0x90 drivers/net/wireguard/timers.c:215
> > >
> > > The line of hlist_add_head that it's hitting is:
> > >
> > > static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
> > > {
> > > struct hlist_node *first = h->first;
> > > WRITE_ONCE(n->next, first);
> > > if (first)
> > >
> > > So that means it's the dereferencing of h that's a problem. That comes from:
> > >
> > > static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
> > > unsigned int idx, unsigned long bucket_expiry)
> > > {
> > >
> > > hlist_add_head(&timer->entry, base->vectors + idx);
> > >
> > > That means it concerns base->vectors + idx, not the timer_list object
> > > that wireguard manages. That's confusing. Could that imply that the
> > > bug is in freeing a previous timer without removing it from the timer
> > > lists, so that it winds up being in base->vectors?
>
> Good point, it's indeed likely that the timer list is messed up already,
> just an unlucky encounter in the wireguard code.
>
> > Digging around on syzkaller, it looks like there's a similar bug on
> > jbd2, concerning iptunnels's allocation:
> >
> > https://syzkaller.appspot.com/text?tag=CrashReport&x=13afb19cd00000
> [...]
> > It might not actually be a wireguard bug?
>
> I wonder whether syzbot reported similar issues with
> CONFIG_KASAN_SW_TAGS. It shouldn't be that different from the HW_TAGS
> but at least we can rule out qemu bugs with the MTE emulation.

+Eric