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

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Message-ID: <58cef9e0-69de-efdb-4035-7c1ed3d23132@tessares.net>
Date:   Wed, 18 Aug 2021 10:02:46 +0200
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     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

Hello,

On 18/08/2021 00:21, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit c4512c63b1193c73b3f09c598a6d0a7f88da1dd8
> Author: Matthieu Baerts <matthieu.baerts@...sares.net>
> Date:   Fri Jun 25 21:25:22 2021 +0000
> 
>     mptcp: fix 'masking a bool' warning
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=122b0655300000
> start commit:   b9011c7e671d Add linux-next specific files for 20210816
> git tree:       linux-next
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=112b0655300000
> console output: https://syzkaller.appspot.com/x/log.txt?x=162b0655300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a245d1aa4f055cc1
> dashboard link: https://syzkaller.appspot.com/bug?extid=7b938780d5deeaaf938f
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=157a41ee300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14f78ff9300000

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.

Cheers,
Matt
-- 
Tessares | Belgium | Hybrid Access Solutions
www.tessares.net