Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <000000000000c0b11d05fa917fe3@google.com> <ZGzfzEs-vJcZAySI@zx2c4.com>
 <20230523090512.19ca60b6@kernel.org> <CANn89iLVSiO1o1C-P30_3i19Ci8W1jQk9mr-_OMsQ4tS8Nq2dg@mail.gmail.com>
 <20230523094108.0c624d47@kernel.org> <CAHmME9obRJPrjiJE95JZug0r6NUwrwwWib+=LO4jiQf-y2m+Vg@mail.gmail.com>
 <20230523094736.3a9f6f8c@kernel.org> <ZGzxa18w-v8Dsy5D@zx2c4.com>
In-Reply-To: <ZGzxa18w-v8Dsy5D@zx2c4.com>
From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 23 May 2023 19:05:27 +0200
Message-ID: <CANn89iLrP7-NbE1yU_okruVKqbuUc3gxPABq4-vQ4SKrUhEdtA@mail.gmail.com>
Subject: Re: [syzbot] [wireguard?] KASAN: slab-use-after-free Write in enqueue_timer
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Jakub Kicinski <kuba@kernel.org>,
        syzbot <syzbot+c2775460db0e1c70018e@syzkaller.appspotmail.com>,
        netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        davem@davemloft.net, linux-kernel@vger.kernel.org,
        pabeni@redhat.com, wireguard@lists.zx2c4.com, jann@thejh.net
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Tue, May 23, 2023 at 7:01=E2=80=AFPM Jason A. Donenfeld <Jason@zx2c4.com=
> wrote:
>
> On Tue, May 23, 2023 at 09:47:36AM -0700, Jakub Kicinski wrote:
> > On Tue, 23 May 2023 18:42:53 +0200 Jason A. Donenfeld wrote:
> > > > It should, no idea why it isn't. Looking thru the code now I don't =
see
> > > > any obvious gaps where timer object is on a list but not active :S
> > > > There's no way to get a vmcore from syzbot, right? :)
> > > >
> > > > Also I thought the shutdown leads to a warning when someone tries t=
o
> > > > schedule the dead timer but in fact add_timer() just exits cleanly.
> > > > So the shutdown won't help us find the culprit :(
> > >
> > > Worth noting that it could also be caused by adding to a dead timer
> > > anywhere in priv_data of another netdev, not just the sole timer_list
> > > in net_device.
> >
> > Oh, I thought you zero'ed in on the watchdog based on offsets.
> > Still, object debug should track all timers in the slab and complain
> > on the free path.
>
> No, I mentioned watchdog because it's the only timer_list in struct
> net_device.
>
> Offset analysis is an interesting idea though. Look at this:
>
> > The buggy address belongs to the object at ffff88801ecc0000
> >  which belongs to the cache kmalloc-cg-8k of size 8192
> > The buggy address is located 5376 bytes inside of
> >  freed 8192-byte region [ffff88801ecc0000, ffff88801ecc2000)
>
> IDA says that for syzkaller's vmlinux, net_device has a size of 0xc80
> and wg_device has a size of 0x880. 0xc80+0x880=3D5376. Coincidence that
> the address offset is just after what wg uses?


Note that the syzkaller report mentioned:

alloc_netdev_mqs+0x89/0xf30 net/core/dev.c:10626
 usbnet_probe+0x196/0x2770 drivers/net/usb/usbnet.c:1698
 usb_probe_interface+0x5c4/0xb00 drivers/usb/core/driver.c:396
 really_probe+0x294/0xc30 drivers/base/dd.c:658
 __driver_probe_device+0x1a2/0x3d0 drivers/base/dd.c:800
 driver_probe_device+0x50/0x420 drivers/base/dd.c:830
 __device_attach_driver+0x2d3/0x520 drivers/base/dd.c:958

So maybe an usbnet driver has a timer_list in its priv_data.