[syzbot] [bridge?] [netfilter?] WARNING in br_nf_local_in

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 08b06c30a445 Merge tag 'v6.17-rc4-ksmbd-fix' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12e3087c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b7511150b112b9c3
dashboard link: https://syzkaller.appspot.com/bug?extid=aa8e2b2bfec0dd8e7e81
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-08b06c30.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0e152fe53de2/vmlinux-08b06c30.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5a1bd9f48488/bzImage-08b06c30.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aa8e2b...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 3 PID: 8841 at net/bridge/br_netfilter_hooks.c:630 br_nf_local_in+0x714/0x7f0 net/bridge/br_netfilter_hooks.c:630
Modules linked in:
CPU: 3 UID: 0 PID: 8841 Comm: syz.0.801 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:br_nf_local_in+0x714/0x7f0 net/bridge/br_netfilter_hooks.c:630
Code: 12 f7 4b f7 90 0f 0b 90 e9 e1 fb ff ff e8 04 f7 4b f7 be 03 00 00 00 48 89 ef e8 87 e8 73 fa e9 39 fa ff ff e8 ed f6 4b f7 90 <0f> 0b 90 e9 dc fd ff ff 4c 89 f7 e8 2c 56 b2 f7 e9 48 f9 ff ff 4c
RSP: 0018:ffffc9000500efc0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff8a6f9520
RDX: ffff8880255b4880 RSI: ffffffff8a6f9743 RDI: 0000000000000001
RBP: ffff88803a6b2900 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000008
R13: ffff88803a6b29c0 R14: 0000000000000000 R15: ffff88803608d874
FS: 00007faf552176c0(0000) GS:ffff8880d69b8000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007faf55216f98 CR3: 000000001fa82000 CR4: 0000000000352ef0
Call Trace:
<TASK>
nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
nf_hook_slow+0xbe/0x200 net/netfilter/core.c:623
nf_hook.constprop.0+0x3e7/0x6b0 include/linux/netfilter.h:273
NF_HOOK include/linux/netfilter.h:316 [inline]
br_pass_frame_up+0x307/0x490 net/bridge/br_input.c:70
br_handle_frame_finish+0xf5a/0x1ca0 net/bridge/br_input.c:227
br_nf_hook_thresh+0x307/0x410 net/bridge/br_netfilter_hooks.c:1170
br_nf_pre_routing_finish+0x8a1/0x1810 net/bridge/br_netfilter_hooks.c:425
NF_HOOK include/linux/netfilter.h:318 [inline]
NF_HOOK include/linux/netfilter.h:312 [inline]
br_nf_pre_routing+0xf7b/0x15b0 net/bridge/br_netfilter_hooks.c:534
nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
nf_hook_bridge_pre net/bridge/br_input.c:283 [inline]
br_handle_frame+0xad5/0x14b0 net/bridge/br_input.c:434
__netif_receive_skb_core.constprop.0+0xa22/0x48c0 net/core/dev.c:5878
__netif_receive_skb_one_core+0xb0/0x1e0 net/core/dev.c:5989
__netif_receive_skb+0x1d/0x160 net/core/dev.c:6104
netif_receive_skb_internal net/core/dev.c:6190 [inline]
netif_receive_skb+0x137/0x7b0 net/core/dev.c:6249
tun_rx_batched.isra.0+0x3ee/0x740 drivers/net/tun.c:1509
tun_get_user+0x28e4/0x3ce0 drivers/net/tun.c:1950
tun_chr_write_iter+0xdc/0x210 drivers/net/tun.c:1996
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x7d3/0x11d0 fs/read_write.c:686
ksys_write+0x12a/0x250 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7faf5438d69f
Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 f9 92 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 4c 93 02 00 48
RSP: 002b:00007faf55217000 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007faf545c5fa0 RCX: 00007faf5438d69f
RDX: 000000000000002a RSI: 0000200000000000 RDI: 00000000000000c8
RBP: 00007faf54411e19 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000002a R11: 0000000000000293 R12: 0000000000000000
R13: 00007faf545c6038 R14: 00007faf545c5fa0 R15: 00007fffb9e76588
</TASK>


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[Florian Westphal]

syzbot <syzbot+aa8e2b...@syzkaller.appspotmail.com> wrote:
> ------------[ cut here ]------------
> WARNING: CPU: 3 PID: 8841 at net/bridge/br_netfilter_hooks.c:630 br_nf_local_in+0x714/0x7f0 net/bridge/br_netfilter_hooks.c:630

#syz fix: netfilter: br_netfilter: do not check confirmed bit in br_nf_local_in() after confirm

[Ido Schimmel]

On Mon, Sep 08, 2025 at 10:13:31PM -0700, syzbot wrote:
> syzbot found the following issue on:
>
> HEAD commit: 08b06c30a445 Merge tag 'v6.17-rc4-ksmbd-fix' of git://git...

Doesn't include this patch:
https://lore.kernel.org/netdev/202508271339...@strlen.de/

Which removed the warning.