Re: KASAN: slab-out-of-bounds Read in vhci_hub_control

[Dmitry Vyukov]

On Wed, Oct 10, 2018 at 8:41 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> On Wed, Oct 3, 2018 at 1:21 AM, Shuah Khan <shuah@xxxxxxxxxx> wrote:
>> On 10/02/2018 10:42 AM, Dmitry Vyukov wrote:
>>> On Tue, Oct 2, 2018 at 6:04 PM, Shuah Khan <shuah@xxxxxxxxxx> wrote:
>>>> On 09/04/2018 12:52 PM, syzbot wrote:
>>>>> Hello,
>>>>>
>>>>> syzbot found the following crash on:
>>>>>
>>>>> HEAD commit:    420f51f4ab6b Merge tag 'arm64-fixes' of git://git.kernel.o..
>>>>> git tree:       upstream
>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=126a6f0e400000
>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=531a917630d2a492
>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=bccc1fe10b70fadc78d0
>>>>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=121caa46400000
>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14ed8ab6400000
>>>>
>>>> C producer doesn't reproduce the problem on 4.19-rc5. Does this C producer
>>>> depend on state of the machine? i.e what is the status of vhci_hcd - are
>>>> there any devices attached?
>>>
>>> Hi Shuah,
>>>
>>> syzbot always runs tests reproducers on a clean machine. There is some
>>> state are running a Debian wheezy init, but no test/fuzz/stress
>>> workload is run before the reproducer.
>>> syzbot also uses VMs, so there are no real devices attached. And it's
>>> GCE VMs (not qemu), and I think GCE does not even emulate any USB
>>> devices.
>>>
>>> An obvious thing to try would be to use the exact commit and config
>>> syzbot gave (rather than 4.19-rc5).
>>> You can also take the image syzbot uses here:
>>> https://github.com/google/syzkaller/blob/master/docs/syzbot.md#crash-does-not-reproduce
>>>
>>>
>>>> I can see the problem looking at the code and fix is easy. However, I would
>>>> like be able to reproduce it and verify the fix works. Also this would be a
>>>> good regression for the driver I could consider adding to selftests.
>>>
>>> syzbot can test fixes for bugs with reproducers:
>>> https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches
>>> So it can test your fix. But this obviously won't help with a test.
>>>
>>
>> Tried the same config and no luck. Any chance you have the complete dmesg?
>
> By "complete" you mean "from the boot"? If yes, then no, we don't keep
> it, full output can be huge and it's not a moving part.
>
> I've captured boot output from another similar machine, unfortunately
> dmesg buffer is not large enough to fit it all, so not sure if you
> will find what you are looking for there:
> https://gist.githubusercontent.com/dvyukov/11b83aeda0466a0f171451d86ab36e15/raw/57121db6cf1bbb5e57c08746241b03904bde95f6/gistfile1.txt


Here is all vhci stuff in /sys if it help.
But it's really just a VM with no hardware, so should be reproducible
everywhere.

root@syzkaller:~# find /sys -name "*vhci*"
/sys/class/misc/vhci
/sys/devices/platform/vhci_hcd.15
/sys/devices/platform/vhci_hcd.13
/sys/devices/platform/vhci_hcd.8
/sys/devices/platform/vhci_hcd.11
/sys/devices/platform/vhci_hcd.6
/sys/devices/platform/vhci_hcd.4
/sys/devices/platform/vhci_hcd.2
/sys/devices/platform/vhci_hcd.0
/sys/devices/platform/vhci_hcd.14
/sys/devices/platform/vhci_hcd.9
/sys/devices/platform/vhci_hcd.12
/sys/devices/platform/vhci_hcd.7
/sys/devices/platform/vhci_hcd.10
/sys/devices/platform/vhci_hcd.5
/sys/devices/platform/vhci_hcd.3
/sys/devices/platform/vhci_hcd.1
/sys/devices/virtual/misc/vhci
/sys/bus/platform/devices/vhci_hcd.15
/sys/bus/platform/devices/vhci_hcd.13
/sys/bus/platform/devices/vhci_hcd.8
/sys/bus/platform/devices/vhci_hcd.11
/sys/bus/platform/devices/vhci_hcd.6
/sys/bus/platform/devices/vhci_hcd.4
/sys/bus/platform/devices/vhci_hcd.2
/sys/bus/platform/devices/vhci_hcd.0
/sys/bus/platform/devices/vhci_hcd.14
/sys/bus/platform/devices/vhci_hcd.9
/sys/bus/platform/devices/vhci_hcd.12
/sys/bus/platform/devices/vhci_hcd.7
/sys/bus/platform/devices/vhci_hcd.10
/sys/bus/platform/devices/vhci_hcd.5
/sys/bus/platform/devices/vhci_hcd.3
/sys/bus/platform/devices/vhci_hcd.1
/sys/bus/platform/drivers/vhci_hcd
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.15
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.13
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.8
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.11
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.6
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.4
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.2
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.0
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.14
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.9
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.12
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.7
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.10
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.5
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.3
/sys/bus/platform/drivers/vhci_hcd/vhci_hcd.1
/sys/module/hci_vhci