[syzbot] [bridge?] KCSAN: data-race in br_fdb_update / br_fdb_update (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f0b9d8eb98df Merge tag 'nfsd-6.19-3' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1304c922580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=bfab43087ad57222ce96
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/f91c35600c27/disk-f0b9d8eb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9edb3553b7a5/vmlinux-f0b9d8eb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4d762ee145b8/bzImage-f0b9d8eb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bfab43...@syzkaller.appspotmail.com

bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
==================================================================
BUG: KCSAN: data-race in br_fdb_update / br_fdb_update

read to 0xffff88811a0655c0 of 8 bytes by interrupt on cpu 1:
br_fdb_update+0x106/0x460 net/bridge/br_fdb.c:1005
br_handle_frame_finish+0x340/0xfc0 net/bridge/br_input.c:144
br_nf_hook_thresh+0x1eb/0x220 net/bridge/br_netfilter_hooks.c:-1
br_nf_pre_routing_finish_ipv6+0x4d1/0x570 net/bridge/br_netfilter_ipv6.c:-1
NF_HOOK include/linux/netfilter.h:318 [inline]
br_nf_pre_routing_ipv6+0x1fa/0x2b0 net/bridge/br_netfilter_ipv6.c:184
br_nf_pre_routing+0x52b/0xbd0 net/bridge/br_netfilter_hooks.c:508
nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
nf_hook_bridge_pre net/bridge/br_input.c:291 [inline]
br_handle_frame+0x4f0/0x9e0 net/bridge/br_input.c:442
__netif_receive_skb_core+0x5df/0x1920 net/core/dev.c:6026
__netif_receive_skb_one_core net/core/dev.c:6137 [inline]
__netif_receive_skb+0x59/0x270 net/core/dev.c:6252
process_backlog+0x228/0x420 net/core/dev.c:6604
__napi_poll+0x5f/0x300 net/core/dev.c:7668
napi_poll net/core/dev.c:7731 [inline]
net_rx_action+0x425/0x8c0 net/core/dev.c:7883
handle_softirqs+0xba/0x290 kernel/softirq.c:622
do_softirq+0x45/0x60 kernel/softirq.c:523
__local_bh_enable_ip+0x70/0x80 kernel/softirq.c:450
local_bh_enable include/linux/bottom_half.h:33 [inline]
__alloc_skb+0x476/0x4b0 net/core/skbuff.c:674
alloc_skb include/linux/skbuff.h:1383 [inline]
wg_socket_send_buffer_to_peer+0x35/0x120 drivers/net/wireguard/socket.c:192
wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:40 [inline]
wg_packet_handshake_send_worker+0x10d/0x160 drivers/net/wireguard/send.c:51
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
worker_thread+0x582/0x770 kernel/workqueue.c:3421
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

write to 0xffff88811a0655c0 of 8 bytes by interrupt on cpu 0:
br_fdb_update+0x13e/0x460 net/bridge/br_fdb.c:1006
br_handle_frame_finish+0x340/0xfc0 net/bridge/br_input.c:144
br_nf_hook_thresh+0x1eb/0x220 net/bridge/br_netfilter_hooks.c:-1
br_nf_pre_routing_finish_ipv6+0x4d1/0x570 net/bridge/br_netfilter_ipv6.c:-1
NF_HOOK include/linux/netfilter.h:318 [inline]
br_nf_pre_routing_ipv6+0x1fa/0x2b0 net/bridge/br_netfilter_ipv6.c:184
br_nf_pre_routing+0x52b/0xbd0 net/bridge/br_netfilter_hooks.c:508
nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
nf_hook_bridge_pre net/bridge/br_input.c:291 [inline]
br_handle_frame+0x4f0/0x9e0 net/bridge/br_input.c:442
__netif_receive_skb_core+0x5df/0x1920 net/core/dev.c:6026
__netif_receive_skb_one_core net/core/dev.c:6137 [inline]
__netif_receive_skb+0x59/0x270 net/core/dev.c:6252
process_backlog+0x228/0x420 net/core/dev.c:6604
__napi_poll+0x5f/0x300 net/core/dev.c:7668
napi_poll net/core/dev.c:7731 [inline]
net_rx_action+0x425/0x8c0 net/core/dev.c:7883
handle_softirqs+0xba/0x290 kernel/softirq.c:622
do_softirq+0x45/0x60 kernel/softirq.c:523
__local_bh_enable_ip+0x70/0x80 kernel/softirq.c:450
local_bh_enable include/linux/bottom_half.h:33 [inline]
fpregs_unlock arch/x86/include/asm/fpu/api.h:77 [inline]
kernel_fpu_end+0x6c/0x80 arch/x86/kernel/fpu/core.c:480
blake2s_compress+0x67/0x1740 lib/crypto/x86/blake2s.h:42
blake2s_update+0xa3/0x160 lib/crypto/blake2s.c:119
hmac+0x141/0x270 drivers/net/wireguard/noise.c:324
kdf+0x10b/0x1d0 drivers/net/wireguard/noise.c:375
mix_dh drivers/net/wireguard/noise.c:413 [inline]
wg_noise_handshake_create_initiation+0x1ac/0x520 drivers/net/wireguard/noise.c:550
wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:34 [inline]
wg_packet_handshake_send_worker+0xb2/0x160 drivers/net/wireguard/send.c:51
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
worker_thread+0x582/0x770 kernel/workqueue.c:3421
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

value changed: 0x0000000100026abc -> 0x0000000100026abd

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 8678 Comm: kworker/u8:42 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: wg-kex-wg0 wg_packet_handshake_send_worker
==================================================================
net_ratelimit: 6540 callbacks suppressed
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:aa, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:aa, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:96:6e:14:75:db:9d, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:96:6e:14:75:db:9d, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
net_ratelimit: 7050 callbacks suppressed
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:aa, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:aa, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:96:6e:14:75:db:9d, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:96:6e:14:75:db:9d, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)


---
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 syzk...@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

[Eric Dumazet]

I am taking care of this issue, I will add the syzbot tags when sending V3 of

https://lore.kernel.org/netdev/CANn89iLaMpL1Kz=t13b0eGZ+m5dBxUpX...@mail.gmail.com/T/#m19446ad4b132da817bda52a98a77a815034ed020

Thanks !