Re: [syzbot] [net?] WARNING in l2tp_exit_net

[James Chapman <jchapman@katalix.com>]

On 13/09/2024 03:49, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f3b6129b7d25 Merge branch '100GbE' of git://git.kernel.org..
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=144ba477980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=37742f4fda0d1b09
> dashboard link: https://syzkaller.appspot.com/bug?extid=332fe1e67018625f63c9
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/a742e7b2e0d2/disk-f3b6129b.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/6982186745fb/vmlinux-f3b6129b.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/5fd38b217bb5/bzImage-f3b6129b.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+332fe1e67018625f63c9@syzkaller.appspotmail.com
> 
> bond0 (unregistering): (slave dummy0): Releasing backup interface
> bond0 (unregistering): Released all slaves
> tipc: Disabling bearer <eth:batadv0>
> tipc: Disabling bearer <udp:syz0>
> tipc: Left network mode
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 17026 at net/l2tp/l2tp_core.c:1881 l2tp_exit_net+0x165/0x170 net/l2tp/l2tp_core.c:1881
> Modules linked in:
> CPU: 0 UID: 0 PID: 17026 Comm: kworker/u8:36 Not tainted 6.11.0-rc6-syzkaller-01324-gf3b6129b7d25 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
> Workqueue: netns cleanup_net
> RIP: 0010:l2tp_exit_net+0x165/0x170 net/l2tp/l2tp_core.c:1881
> Code: 0f 0b 90 e9 3b ff ff ff e8 48 a4 b0 f6 eb 05 e8 41 a4 b0 f6 90 0f 0b 90 e9 7a ff ff ff e8 33 a4 b0 f6 eb 05 e8 2c a4 b0 f6 90 <0f> 0b 90 eb b5 66 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90
> RSP: 0018:ffffc9000ae07a98 EFLAGS: 00010293
> RAX: ffffffff8ae2e87d RBX: ffff8880797c0888 RCX: ffff88806dbbda00
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
> RBP: ffffc9000ae07bb0 R08: ffffffff8bb2ce16 R09: 1ffffffff2031025
> R10: dffffc0000000000 R11: fffffbfff2031026 R12: dffffc0000000000
> R13: 1ffffffff1fd274c R14: ffff8880797c0930 R15: ffff8880797c0840
> FS:  0000000000000000(0000) GS:ffff8880b8800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000110c3831d6 CR3: 000000000e734000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   <TASK>
>   ops_exit_list net/core/net_namespace.c:173 [inline]
>   cleanup_net+0x802/0xcc0 net/core/net_namespace.c:626
>   process_one_work kernel/workqueue.c:3231 [inline]
>   process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
>   worker_thread+0x86d/0xd10 kernel/workqueue.c:3389
>   kthread+0x2f0/0x390 kernel/kthread.c:389
>   ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
>   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>   </TASK>

This warning is l2tp checking that there are no l2tp tunnels left when 
l2tp_exit_net is called and finding one or more tunnels still in its IDR 
list. These should be removed by l2tp_pre_exit_net.

I'll review l2tp code and watch this one.

> 
> ---
> 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@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
>