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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 16 Feb 2021 19:15:04 +0100
Message-ID: <CACT4Y+ZH4ViZix7qyPPXtcgaanimm8CmSu1J8qhqpEedxC=fmQ@mail.gmail.com>
Subject: Re: KASAN: invalid-access Write in enqueue_timer
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Eric Dumazet <edumazet@google.com>
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Netdev <netdev@vger.kernel.org>,
        syzbot <syzbot+95c862be69e37145543f@syzkaller.appspotmail.com>,
        Mark Brown <broonie@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, mbenes@suse.cz,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>
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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