linux-kernel - Re: [syzbot] KFENCE: use-after-free in kvm_fastop

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Message-ID: <f9c5ec7f-4014-c073-164f-5152111c1d31@tessares.net>
Date:   Wed, 18 Aug 2021 10:57:36 +0200
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Pavel Skripkin <paskripkin@...il.com>,
        syzbot <syzbot+7b938780d5deeaaf938f@...kaller.appspotmail.com>,
        davem@...emloft.net, johan.hedberg@...il.com, kuba@...nel.org,
        linux-bluetooth@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, luiz.dentz@...il.com,
        marcel@...tmann.org, mathew.j.martineau@...ux.intel.com,
        netdev@...r.kernel.org, pabeni@...hat.com,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: [syzbot] KFENCE: use-after-free in kvm_fastop_exception

On 18/08/2021 10:55, Pavel Skripkin wrote:
> On 8/18/21 11:21 AM, Matthieu Baerts wrote:
>> Hi Pavel,
>>
> [snip]
>>>>
>>>> I'm pretty sure the commit c4512c63b119 ("mptcp: fix 'masking a bool'
>>>> warning") doesn't introduce the reported bug. This minor fix is
>>>> specific
>>>> to MPTCP which doesn't seem to be used here.
>>>>
>>>> I'm not sure how I can tell syzbot this is a false positive.
>>>>
>>>
>>>
>>> looks like it's fs/namei bug. Similar reports:
>>>
>>> https://syzkaller.appspot.com/bug?id=517fa734b92b7db404c409b924cf5c997640e324
>>>
>>>
>>>
>>> https://syzkaller.appspot.com/bug?id=484483daf3652b40dae18531923aa9175d392a4d
>>>
>>
>> Thank you for having checked!
>> Should we mark them as "#syz dup" if you think they have the same root
>> cause?
>>
> 
> I think, yes, but I want to receive feedback from fs people about this
> bug. There were huge updates last month, and, maybe, I am missing some
> details. Alloc/free calltrace is the same, but anyway, I want some
> confirmation to not close different bugs by mistake :)
> 
> If these bugs really have same root case I will close them manually
> after fix posted.

Thank you for the explanation. Sounds good to me!

Cheers,
Matt
-- 
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