Re: net/ipv4: use-after-free in ip_queue_xmit

[Andrey Konovalov]

On Thu, Apr 13, 2017 at 9:59 PM, Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
> On Thu, Apr 13, 2017 at 11:49 AM, Andrey Konovalov
> <andreyknvl@xxxxxxxxxx> wrote:
>> On Mon, Apr 10, 2017 at 7:46 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>>> On Mon, Apr 10, 2017 at 7:42 PM, Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
>>>> On Mon, Apr 10, 2017 at 7:40 AM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>>>>> Hi,
>>>>>
>>>>> I've got the following error report while fuzzing the kernel with syzkaller.
>>>>>
>>>>> On commit 39da7c509acff13fc8cb12ec1bb20337c988ed36 (4.11-rc6).
>>>>>
>>>>> Unfortunately it's not reproducible.
>>>>>
>>>>> BUG: KASAN: use-after-free in ip_select_ttl include/net/dst.h:176
>>>>> [inline] at addr ffff88006ab3602c
>>>>> BUG: KASAN: use-after-free in ip_queue_xmit+0x1817/0x1a30
>>>>> net/ipv4/ip_output.c:485 at addr ffff88006ab3602c
>>>>> Read of size 4 by task syz-executor1/12627
>>>>> CPU: 3 PID: 12627 Comm: syz-executor1 Not tainted 4.11.0-rc6+ #206
>>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>>>> Call Trace:
>>>>>  __dump_stack lib/dump_stack.c:16 [inline]
>>>>>  dump_stack+0x292/0x398 lib/dump_stack.c:52
>>>>>  kasan_object_err+0x1c/0x70 mm/kasan/report.c:164
>>>>>  print_address_description mm/kasan/report.c:202 [inline]
>>>>>  kasan_report_error mm/kasan/report.c:291 [inline]
>>>>>  kasan_report+0x252/0x510 mm/kasan/report.c:347
>>>>>  __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:367
>>>>>  ip_select_ttl include/net/dst.h:176 [inline]
>>>>
>>>> Probably same as the one you reported on ipv4_mtu(), it would
>>>> be nice if you could test the patch I proposed:
>>>>
>>>> https://patchwork.ozlabs.org/patch/747556/
>>>
>>> Applied your patch.
>>
>> Oops, apparently your patch doesn't compile:
>>
>
> Weird, it compiles fine here. Either you have a different config
> or the following piece is missing for some reason?
>
> @@ -69,6 +69,7 @@  struct rtable {
>
>   struct list_head rt_uncached;
>   struct uncached_list *rt_uncached_list;
> + struct fib_info *fi; /* for refcnt to shared metrics */
>  };

Yes, I don't have this field in the rtable struct.

I'm on 39da7c509acff13fc8cb12ec1bb20337c988ed36 (4.11-rc6).

I also don't see it in the cross reference:
http://lxr.free-electrons.com/source/include/net/route.h#L51

>
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