[syzbot] [net?] WARNING: lock held when returning to user space in ethnl_act_cable_test

[syzbot] [net?] WARNING: lock held when returning to user space in ethnl_act_cable_test

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f9db28bb09f4 Merge branch 'net-redundant-judgments'
git tree:       net-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=115eb015980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=df2f0ed7e30a639d
dashboard link: https://syzkaller.appspot.com/bug?extid=c641161e97237326ea74
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17d2d609980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1741fbf5980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/585e02f7fe7b/disk-f9db28bb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b9faf5d24900/vmlinux-f9db28bb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f9df5868ea4f/bzImage-f9db28bb.xz

The issue was bisected to:

commit 3688ff3077d3f334cee1d4b61d8bfb6a9508c2d2
Author: Maxime Chevallier <maxime.chevallier@bootlin.com>
Date:   Wed Aug 21 15:10:05 2024 +0000

    net: ethtool: cable-test: Target the command to the requested PHY

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=146fcd8d980000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=166fcd8d980000
console output: https://syzkaller.appspot.com/x/log.txt?x=126fcd8d980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c641161e97237326ea74@syzkaller.appspotmail.com
Fixes: 3688ff3077d3 ("net: ethtool: cable-test: Target the command to the requested PHY")

================================================
WARNING: lock held when returning to user space!
6.11.0-rc4-syzkaller-00565-gf9db28bb09f4 #0 Not tainted
------------------------------------------------
syz-executor124/5240 is leaving the kernel with locks still held!
1 lock held by syz-executor124/5240:
 #0: ffffffff8fc84b88 (rtnl_mutex){+.+.}-{3:3}, at: ethnl_act_cable_test+0x187/0x3f0 net/ethtool/cabletest.c:74


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Re: [syzbot] [net?] WARNING: lock held when returning to user space in ethnl_act_cable_test

[Maxime Chevallier]

Hello,

On Mon, 26 Aug 2024 01:50:24 -0700
syzbot <syzbot+c641161e97237326ea74@syzkaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f9db28bb09f4 Merge branch 'net-redundant-judgments'
> git tree:       net-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=115eb015980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=df2f0ed7e30a639d
> dashboard link: https://syzkaller.appspot.com/bug?extid=c641161e97237326ea74
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17d2d609980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1741fbf5980000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/585e02f7fe7b/disk-f9db28bb.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b9faf5d24900/vmlinux-f9db28bb.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/f9df5868ea4f/bzImage-f9db28bb.xz
> 
> The issue was bisected to:
> 
> commit 3688ff3077d3f334cee1d4b61d8bfb6a9508c2d2
> Author: Maxime Chevallier <maxime.chevallier@bootlin.com>
> Date:   Wed Aug 21 15:10:05 2024 +0000
> 
>     net: ethtool: cable-test: Target the command to the requested PHY
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=146fcd8d980000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=166fcd8d980000
> console output: https://syzkaller.appspot.com/x/log.txt?x=126fcd8d980000

Looks like there's indeed a mistake in the error path for that command,
I'll send a fix for that.

Thanks,

Maxime