netdev - Re: [syzbot] general protection fault in percpu_ref

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Message-ID: <YUl6VZhPHBqAx+6g@zeniv-ca.linux.org.uk>
Date:   Tue, 21 Sep 2021 06:23:17 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     syzbot <syzbot+533f389d4026d86a2a95@...kaller.appspotmail.com>
Cc:     andrii@...nel.org, ast@...nel.org, axboe@...nel.dk,
        bpf@...r.kernel.org, cgroups@...r.kernel.org,
        christian.brauner@...ntu.com, christian@...uner.io,
        daniel@...earbox.net, dkadashev@...il.com, hannes@...xchg.org,
        john.fastabend@...il.com, kafai@...com, kpsingh@...nel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        lizefan.x@...edance.com, netdev@...r.kernel.org,
        songliubraving@...com, syzkaller-bugs@...glegroups.com,
        tj@...nel.org, torvalds@...ux-foundation.org, yhs@...com
Subject: Re: [syzbot] general protection fault in percpu_ref_put

On Mon, Sep 20, 2021 at 07:55:16PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    4357f03d6611 Merge tag 'pm-5.15-rc2' of git://git.kernel.o..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=173e2d27300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ccfb8533b1cbe3b1
> dashboard link: https://syzkaller.appspot.com/bug?extid=533f389d4026d86a2a95
> compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1395c6f1300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11568cad300000
> 
> The issue was bisected to:
> 
> commit 020250f31c4c75ac7687a673e29c00786582a5f4
> Author: Dmitry Kadashev <dkadashev@...il.com>
> Date:   Thu Jul 8 06:34:43 2021 +0000
> 
>     namei: make do_linkat() take struct filename
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=137e8a4b300000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=10fe8a4b300000
> console output: https://syzkaller.appspot.com/x/log.txt?x=177e8a4b300000

I would be very surprised if that was true.  After the first step of bisect
you've traded one oops for another, and *that* went to do_linkat() breakage.
Which should be fixed by fdfc346302a7.

Look at the oopsen - initial and final ones look very different.