Re: [syzbot] KFENCE: use-after-free in kvm_fastop_exception

Matthieu Baerts
2021-08-18T08:05:03Z

Hello,

On 18/08/2021 00:21, syzbot wrote:
> syzbot has bisected this issue to:
>
> commit c4512c63b1193c73b3f09c598a6d0a7f88da1dd8
> Author: Matthieu Baerts <matthieu.baerts@tessares.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