linux-kernel - Re: [syzbot] KASAN: slab-out-of-bounds Read in copy

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Message-ID: <57f9eace-c721-1c33-e080-135df4087606@redhat.com>
Date:   Wed, 27 Oct 2021 09:31:25 +0200
From:   Laurent Vivier <lvivier@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        syzbot <syzbot+b86736b5935e0d25b446@...kaller.appspotmail.com>,
        davem@...emloft.net, herbert@...dor.apana.org.au, jiri@...dia.com,
        kuba@...nel.org, leonro@...dia.com, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, mpm@...enic.com,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: slab-out-of-bounds Read in copy_data

On 27/10/2021 09:20, Michael S. Tsirkin wrote:
> On Wed, Oct 27, 2021 at 09:08:04AM +0200, Laurent Vivier wrote:
>> On 27/10/2021 00:34, Eric Dumazet wrote:
>>>
>>>
>>> On 10/26/21 9:39 AM, 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@...dia.com>
>>>> Date:   Thu Oct 21 14:16:14 2021 +0000
>>>>
>>>>       devlink: Remove not-executed trap policer notifications
>>>
>>> More likely this came with
>>>
>>> caaf2874ba27b92bca6f0298bf88bad94067ec37 hwrng: virtio - don't waste entropy
>>>
>>
>> I'm going to have a look.
>>
>> Thanks,
>> Laurent
> 
> How bad is it if we just drop this and waste some bytes of entropy?
> 

I don't think it's bad at all. In most of the cases we should use the full buffer.

So, you can drop, I will re-submit them later with a fix.

Thanks,
Laurent