linux-kernel - Re: [syzbot] [netfilter?] WARNING in __nf_unregister_net

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Message-ID: <69049df6.050a0220.e9cb8.000c.GAE@google.com>
Date: Fri, 31 Oct 2025 04:31:02 -0700
From: syzbot <syzbot+78ac1e46d2966eb70fda@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, phil@....cc, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [netfilter?] WARNING in __nf_unregister_net_hook (9)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in nf_hook_entry_head

------------[ cut here ]------------
WARNING: CPU: 0 PID: 36 at net/netfilter/core.c:329 nf_hook_entry_head+0x23e/0x2c0 net/netfilter/core.c:329
Modules linked in:
CPU: 0 UID: 0 PID: 36 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: netns cleanup_net
RIP: 0010:nf_hook_entry_head+0x23e/0x2c0 net/netfilter/core.c:329
Code: 4c 89 f8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 4c 89 ff e8 7d b9 b6 f8 4d 39 37 74 36 e8 53 04 51 f8 90 <0f> 0b 90 31 db 48 89 d8 5b 41 5e 41 5f 5d c3 cc cc cc cc cc e8 39
RSP: 0018:ffffc90000ac7768 EFLAGS: 00010293
RAX: ffffffff896eff5b RBX: ffff888030a98000 RCX: ffff8881416b9e40
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffff8881416b9e40 R09: 0000000000000006
R10: 000000000000000a R11: 0000000000000000 R12: ffff888020ec8000
R13: 0000000000000005 R14: ffff888020ec8000 R15: ffff888030a98108
FS:  0000000000000000(0000) GS:ffff88812613e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2e4b7156c0 CR3: 000000000dd38000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __nf_unregister_net_hook+0x74/0x700 net/netfilter/core.c:491
 nft_unregister_flowtable_ops net/netfilter/nf_tables_api.c:8977 [inline]
 __nft_unregister_flowtable_net_hooks net/netfilter/nf_tables_api.c:8992 [inline]
 __nft_release_hook+0x180/0x350 net/netfilter/nf_tables_api.c:11985
 __nft_release_hooks net/netfilter/nf_tables_api.c:11999 [inline]
 nf_tables_pre_exit_net+0xa7/0x110 net/netfilter/nf_tables_api.c:12150
 ops_pre_exit_list net/core/net_namespace.c:161 [inline]
 ops_undo_list+0x187/0x990 net/core/net_namespace.c:234
 cleanup_net+0x4d8/0x820 net/core/net_namespace.c:696
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


Tested on:

commit:         0d0eb186 cxgb4: flower: add support for fragmentation
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=162a7fe2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5683686a5f7ee53f
dashboard link: https://syzkaller.appspot.com/bug?extid=78ac1e46d2966eb70fda
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Note: no patches were applied.