Subject: [syzbot] [netfilter?] WARNING in nf_conntrack_cleanup_net_list

From: syzbot <[email-masked]>
Date: Thu, 11 Dec 2025 10:38:31 -0800

Hello,

syzbot found the following issue on:

HEAD commit:    5ce74bc1b7cb Add linux-next specific files for 20251211
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11a241b4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=4393c47753b7808dac7d
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e1660176a50f/disk-5ce74bc1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/616ede012bbd/vmlinux-5ce74bc1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7c0c5bc40fd8/bzImage-5ce74bc1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

------------[ cut here ]------------
conntrack cleanup blocked for 60s
WARNING: net/netfilter/nf_conntrack_core.c:2512 at nf_conntrack_cleanup_net_list+0x234/0x340 net/netfilter/nf_conntrack_core.c:2511, CPU#1: kworker/u8:0/12
Modules linked in:
CPU: 1 UID: 0 PID: 12 Comm: kworker/u8:0 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: netns cleanup_net
RIP: 0010:nf_conntrack_cleanup_net_list+0x234/0x340 net/netfilter/nf_conntrack_core.c:2511
Code: 08 48 89 df e8 fd 78 a3 f8 4c 8b 3b 49 39 df 74 69 e8 20 16 3d f8 45 31 e4 e9 8e fe ff ff e8 13 16 3d f8 48 8d 3d ec 2f 0c 06 <67> 48 0f b9 3a eb c0 89 e9 80 e1 07 80 c1 03 38 c1 0f 8c cd fe ff
RSP: 0018:ffffc90000117870 EFLAGS: 00010293
RAX: ffffffff8984a13d RBX: ffffc90000117a00 RCX: ffff88801ce8db80
RDX: 0000000000000000 RSI: ffffffffffffffcb RDI: ffffffff8f90d130
RBP: 0000000000000001 R08: ffff88807ce6b003 R09: 1ffff1100f9cd600
R10: dffffc0000000000 R11: ffffed100f9cd601 R12: 0000000000000001
R13: dffffc0000000000 R14: 00000001000068e3 R15: 0000000100006918
FS:  0000000000000000(0000) GS:ffff888125f32000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000020000 CR3: 00000000306ac000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ops_exit_list net/core/net_namespace.c:205 [inline]
 ops_undo_list+0x525/0x990 net/core/net_namespace.c:252
 cleanup_net+0x4d8/0x7a0 net/core/net_namespace.c:696
 process_one_work+0x93a/0x15a0 kernel/workqueue.c:3279
 process_scheduled_works kernel/workqueue.c:3362 [inline]
 worker_thread+0x9b0/0xee0 kernel/workqueue.c:3443
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
----------------
Code disassembly (best guess):
   0:	08 48 89             	or     %cl,-0x77(%rax)
   3:	df e8                	fucomip %st(0),%st
   5:	fd                   	std
   6:	78 a3                	js     0xffffffab
   8:	f8                   	clc
   9:	4c 8b 3b             	mov    (%rbx),%r15
   c:	49 39 df             	cmp    %rbx,%r15
   f:	74 69                	je     0x7a
  11:	e8 20 16 3d f8       	call   0xf83d1636
  16:	45 31 e4             	xor    %r12d,%r12d
  19:	e9 8e fe ff ff       	jmp    0xfffffeac
  1e:	e8 13 16 3d f8       	call   0xf83d1636
  23:	48 8d 3d ec 2f 0c 06 	lea    0x60c2fec(%rip),%rdi        # 0x60c3016
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb c0                	jmp    0xfffffff1
  31:	89 e9                	mov    %ebp,%ecx
  33:	80 e1 07             	and    $0x7,%cl
  36:	80 c1 03             	add    $0x3,%cl
  39:	38 c1                	cmp    %al,%cl
  3b:	0f                   	.byte 0xf
  3c:	8c cd                	mov    %cs,%ebp
  3e:	fe                   	(bad)
  3f:	ff                   	.byte 0xff

---
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