Re: [syzbot] KASAN: slab-out-of-bounds Read in copy_data

[Laurent Vivier <lvivier@redhat.com>]

On 27/10/2021 18:25, Laurent Vivier wrote:
> On 27/10/2021 17:28, Michael S. Tsirkin wrote:
>> On Wed, Oct 27, 2021 at 03:36:19PM +0200, Dmitry Vyukov wrote:
>>> On Wed, 27 Oct 2021 at 15:11, Laurent Vivier <lvivier@redhat.com> wrote:
>>>>
>>>> On 26/10/2021 18:39, syzbot wrote:
>>>>> Hello,
>>>>>
>>>>> syzbot found the following issue on:
>>>>>
>>>>> HEAD commit:    9ae1fbdeabd3 Add linux-next specific files for 20211025
>>>>> git tree:       linux-next
>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1331363cb00000
>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=aeb17e42bc109064
>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446
>>>>> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for 
>>>>> Debian) 2.35.2
>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=116ce954b00000
>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=132fcf62b00000
>>>>>
>>>>> The issue was bisected to:
>>>>>
>>>>> commit 22849b5ea5952d853547cc5e0651f34a246b2a4f
>>>>> Author: Leon Romanovsky <leonro@nvidia.com>
>>>>> Date:   Thu Oct 21 14:16:14 2021 +0000
>>>>>
>>>>>       devlink: Remove not-executed trap policer notifications
>>>>>
>>>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=137d8bfcb00000
>>>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=10fd8bfcb00000
>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=177d8bfcb00000
>>>>>
>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>>>> Reported-by: syzbot+b86736b5935e0d25b446@syzkaller.appspotmail.com
>>>>> Fixes: 22849b5ea595 ("devlink: Remove not-executed trap policer notifications")
>>>>>
>>>>> ==================================================================
>>>>> BUG: KASAN: slab-out-of-bounds in memcpy include/linux/fortify-string.h:225 [inline]
>>>>> BUG: KASAN: slab-out-of-bounds in copy_data+0xf3/0x2e0 
>>>>> drivers/char/hw_random/virtio-rng.c:68
>>>>> Read of size 64 at addr ffff88801a7a1580 by task syz-executor989/6542
>>>>>
>>>>
>>>> I'm not able to reproduce the problem with next-20211026 and the C reproducer.
>>>>
>>>> And reviewing the code in copy_data() I don't see any issue.
>>>>
>>>> Is it possible to know what it the VM configuration used to test it?
>>>
>>> Hi Laurent,
>>>
>>> syzbot used e2-standard-2 GCE VM when that happened.
>>> You can see some info about these VMs under the "VM info" link on the dashboard.
>>
>> Could you pls confirm whether reverting
>> caaf2874ba27b92bca6f0298bf88bad94067ec37 addresses this?
>>
> 
> I've restarted the syzbot on top of "hwrng: virtio - don't wait on cleanup" [1] and the 
> problem has not been triggered.
> 
> See https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446

The problem seems to be introduced by the last patch:

"hwrng: virtio - always add a pending request"

not

"hwrng: virtio - don't waste entropy"

Thanks,
Laurent

> 
> Thanks,
> Laurent
> 
> [1]
> d721abbeb145 hwrng: virtio - don't wait on cleanup
> bb768beb0a5f hwrng: virtio - add an internal buffer
> d25f27432f80 (origin/master, origin/HEAD, master) Merge tag 'arm-soc-fixes-5.15-3' of 
> git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc
>