linux-kernel - Re: unregister_netdevice: waiting for DEV to become free (4)

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Date:   Wed, 19 Aug 2020 16:03:33 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+df400f2f24a1677cd7e0@...kaller.appspotmail.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        bpf <bpf@...r.kernel.org>
Subject: Re: unregister_netdevice: waiting for DEV to become free (4)

On Wed, Aug 19, 2020 at 3:54 PM syzbot
<syzbot+df400f2f24a1677cd7e0@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    18445bf4 Merge tag 'spi-fix-v5.9-rc1' of git://git.kernel...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1710d97a900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=bb68b9e8a8cc842f
> dashboard link: https://syzkaller.appspot.com/bug?extid=df400f2f24a1677cd7e0
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15859986900000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1228fea1900000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+df400f2f24a1677cd7e0@...kaller.appspotmail.com
>
> unregister_netdevice: waiting for lo to become free. Usage count = 1

Based on the repro, it looks bpf/bpf link related:

syz_emit_ethernet(0x86, &(0x7f0000000000)={@...al, @empty=[0x2],
@void, {@...4={0x800, @udp={{0x5, 0x4, 0x0, 0x0, 0x78, 0x0, 0x0, 0x0,
0x11, 0x0, @empty, @empty}, {0x0, 0x1b59, 0x64, 0x0,
@wg=@...ponse={0x5, 0x0, 0x0, "020000010865390406030500000000010900",
"9384bbeb3018ad591b661fe808b21b77",
{"694c875dfb1be5d2a0057a62022a1564",
"a329d3a73b8268129e5fa4316a5d8c69"}}}}}}}, 0x0)
mkdirat(0xffffffffffffff9c, &(0x7f0000000000)='./file0\x00', 0x0)
mount(0x0, &(0x7f0000000080)='./file0\x00',
&(0x7f0000000040)='cgroup2\x00', 0x0, 0x0)
r0 = openat$cgroup_root(0xffffffffffffff9c, &(0x7f0000000000), 0x200002, 0x0)
r1 = bpf$PROG_LOAD(0x5, &(0x7f0000000080)={0x9, 0x4,
&(0x7f0000000000)=@...med={{}, [@alu={0x8000000201a7f19, 0x0, 0x6,
0x2, 0x1}]}, &(0x7f0000000100)='GPL\x00', 0x0, 0x0, 0x0, 0x0, 0x0, [],
0x0, 0x0, 0xffffffffffffffff, 0x8, 0x0, 0x0, 0x10, 0x0}, 0x70)
bpf$BPF_LINK_CREATE(0x1c, &(0x7f0000000100)={r1, r0, 0x2}, 0x10)

> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches