WARNING in nf_ct_bridge_post

Status: upstream: reported C repro on 2025/11/19 13:14
Subsystems: bridge netfilter
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+a8ba738fe2db6b4bb27f@syzkaller.appspotmail.com
First crash: 249d, last: 2d19h
Cause bisection: failed (error log, bisect log)
  
Fix bisection: failed (error log, bisect log)
  
✨ AI Patch Versions (2)
Version Stage Reported Report Link Job
1 moderation 2026/06/23 15:32 Discussion 4867c9de-cc2a-406b-a01c-4321a64f38ec
1 moderation 2026/05/20 23:14 Discussion d2874cff-e6fe-4bb5-807f-dd0552282866
✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision Error
4867c9de patching WARNING in nf_ct_bridge_post 2026/06/23 14:12 2026/06/23 14:12 2026/06/23 15:32 e30e5c89

			
		
d2874cff patching WARNING in nf_ct_bridge_post 2026/05/20 18:04 2026/05/20 21:31 2026/05/20 23:14 cf874a1c

			
		
b7498e33 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ✅ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ✅ VMHostTrigger: ✅ WARNING in nf_ct_bridge_post 2026/05/12 09:11 2026/05/12 09:11 2026/05/12 11:25 d5b1a17d

			
		
Discussions (4)
Title Replies (including bot) Last reply
[syzbot] Monthly bridge report (May 2026) 0 (1) 2026/05/08 20:32
[syzbot] Monthly bridge report (Apr 2026) 0 (1) 2026/04/07 20:34
[syzbot] Monthly netfilter report (Mar 2026) 0 (1) 2026/03/31 08:07
[syzbot] [bridge?] [netfilter?] WARNING in nf_ct_bridge_post 0 (1) 2025/11/19 13:14
Last patch testing requests (10)
Created Duration User Patch Repo Result
2026/07/18 14:50 21m retest repro upstream error
2026/07/04 13:37 25m retest repro upstream report log
2026/07/04 13:37 25m retest repro upstream report log
2026/06/20 19:11 27m retest repro net log
2026/05/16 21:12 38m retest repro net-next log
2026/05/16 21:12 25m retest repro net-next log
2026/04/25 12:36 22m retest repro upstream error
2026/04/25 12:36 21m retest repro upstream error
2026/04/25 12:36 21m retest repro upstream error
2026/04/11 12:02 28m retest repro net report log

Sample crash report:
------------[ cut here ]------------
1
WARNING: net/bridge/netfilter/nf_conntrack_bridge.c:356 at nf_ct_bridge_refrag net/bridge/netfilter/nf_conntrack_bridge.c:356 [inline], CPU#0: syz.3.93/6147
WARNING: net/bridge/netfilter/nf_conntrack_bridge.c:356 at nf_ct_bridge_post+0x42e/0x1110 net/bridge/netfilter/nf_conntrack_bridge.c:407, CPU#0: syz.3.93/6147
Modules linked in:
CPU: 0 UID: 0 PID: 6147 Comm: syz.3.93 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:nf_ct_bridge_refrag net/bridge/netfilter/nf_conntrack_bridge.c:356 [inline]
RIP: 0010:nf_ct_bridge_post+0x42e/0x1110 net/bridge/netfilter/nf_conntrack_bridge.c:407
Code: 88 f7 49 8b 36 4c 89 ff 48 89 da 48 8d 8c 24 40 01 00 00 49 c7 c0 70 c6 ab 8a e8 0d 46 e1 ff e9 93 09 00 00 e8 53 c6 1a f7 90 <0f> 0b 90 45 31 ff 4c 8b 64 24 18 e9 83 09 00 00 e8 3d c6 1a f7 eb
RSP: 0018:ffffc90003ed6be0 EFLAGS: 00010293
RAX: ffffffff8aabab2d RBX: ffff888074381000 RCX: ffff888027ce1f00
RDX: 0000000000000000 RSI: ffffffff901923e0 RDI: 0000000000000081
RBP: ffffc90003ed6dc0 R08: ffff888027ce1f00 R09: 0000000000000002
R10: 000000000000dd86 R11: 0000000000000000 R12: 0000000000000081
R13: dffffc0000000000 R14: ffffc90003ed6e80 R15: 1ffff1100e870206
FS:  00007f090ebc66c0(0000) GS:ffff888124f54000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7171daeb00 CR3: 0000000077ea8000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_slow+0xc5/0x220 net/netfilter/core.c:619
 nf_hook include/linux/netfilter.h:273 [inline]
 NF_HOOK+0x23e/0x3f0 include/linux/netfilter.h:316
 br_forward_finish+0xd3/0x130 net/bridge/br_forward.c:66
 NF_HOOK+0x360/0x3f0 include/linux/netfilter.h:318
 __br_forward+0x397/0x540 net/bridge/br_forward.c:115
 deliver_clone net/bridge/br_forward.c:131 [inline]
 maybe_deliver net/bridge/br_forward.c:191 [inline]
 br_flood+0x3e6/0x8d0 net/bridge/br_forward.c:245
 br_handle_frame_finish+0x1175/0x1990 net/bridge/br_input.c:229
 nf_hook_bridge_pre net/bridge/br_input.c:313 [inline]
 br_handle_frame+0x81b/0x1510 net/bridge/br_input.c:442
 __netif_receive_skb_core+0x989/0x30b0 net/core/dev.c:6099
 __netif_receive_skb_one_core net/core/dev.c:6210 [inline]
 __netif_receive_skb net/core/dev.c:6325 [inline]
 netif_receive_skb_internal net/core/dev.c:6411 [inline]
 netif_receive_skb+0x1fe/0xbf0 net/core/dev.c:6470
 tun_rx_batched+0x1de/0x790 drivers/net/tun.c:1518
 tun_get_user+0x2b44/0x4370 drivers/net/tun.c:1986
 tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:2032
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x612/0xba0 fs/read_write.c:687
 ksys_write+0x150/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f090dd5e6ce
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007f090ebc5fb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f090ebc66c0 RCX: 00007f090dd5e6ce
RDX: 000000000000004e RSI: 0000200000000500 RDI: 00000000000000c8
RBP: 00007f090de33eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f090e026128 R14: 00007f090e026090 R15: 00007ffd3fce8af8
 </TASK>

Crashes (10):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/23 18:34 upstream 4539944e5151 71a13572 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce WARNING in nf_ct_bridge_post
2026/07/23 08:16 upstream 4539944e5151 881ce5c2 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce WARNING in nf_ct_bridge_post
2025/11/19 03:57 upstream 5bebe8de1926 ef766cd7 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in nf_ct_bridge_post
2025/11/19 02:07 upstream 5bebe8de1926 ef766cd7 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in nf_ct_bridge_post
2025/11/19 00:25 upstream 5bebe8de1926 ef766cd7 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in nf_ct_bridge_post
2026/03/28 11:01 net 2edfa31769a4 356bdfc9 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce WARNING in nf_ct_bridge_post
2026/03/28 06:15 net 2edfa31769a4 356bdfc9 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce WARNING in nf_ct_bridge_post
2026/05/02 15:05 net-next 0f19519fdd22 a0d91488 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce WARNING in nf_ct_bridge_post
2026/05/01 23:04 net-next edf4bee4215a 753c55b9 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce WARNING in nf_ct_bridge_post
2025/11/18 22:43 upstream 5bebe8de1926 ef766cd7 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in nf_ct_bridge_post
* Struck through repros no longer work on HEAD.