published June 18, 2025
In the Linux kernel, the following vulnerability has been resolved:
vxlan: Annotate FDB data races
The 'used' and 'updated' fields in the FDB entry structure can be
accessed concurrently by multiple threads, leading to reports such as
[1]. Can be reproduced using [2].
Suppress these reports by annotating these accesses using
READ_ONCE() / WRITE_ONCE().
[1]
BUG: KCSAN: data-race in vxlan_xmit / vxlan_xmit
write to 0xffff942604d263a8 of 8 bytes by task 286 on cpu 0:
vxlan_xmit+0xb29/0x2380
dev_hard_start_xmit+0x84/0x2f0
__dev_queue_xmit+0x45a/0x1650
packet_xmit+0x100/0x150
packet_sendmsg+0x2114/0x2ac0
__sys_sendto+0x318/0x330
__x64_sys_sendto+0x76/0x90
x64_sys_call+0x14e8/0x1c00
do_syscall_64+0x9e/0x1a0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
read to 0xffff942604d263a8 of 8 bytes by task 287 on cpu 2:
vxlan_xmit+0xadf/0x2380
dev_hard_start_xmit+0x84/0x2f0
__dev_queue_xmit+0x45a/0x1650
packet_xmit+0x100/0x150
packet_sendmsg+0x2114/0x2ac0
__sys_sendto+0x318/0x330
__x64_sys_sendto+0x76/0x90
x64_sys_call+0x14e8/0x1c00
do_syscall_64+0x9e/0x1a0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
value changed: 0x00000000fffbac6e -> 0x00000000fffbac6f
Reported by Kernel Concurrency Sanitizer on:
CPU: 2 UID: 0 PID: 287 Comm: mausezahn Not tainted 6.13.0-rc7-01544-gb4b270f11a02 #5
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-3.fc41 04/01/2014
[2]
#!/bin/bash
set +H
echo whitelist > /sys/kernel/debug/kcsan
echo !vxlan_xmit > /sys/kernel/debug/kcsan
ip link add name vx0 up type vxlan id 10010 dstport 4789 local 192.0.2.1
bridge fdb add 00:11:22:33:44:55 dev vx0 self static dst 198.51.100.1
taskset -c 0 mausezahn vx0 -a own -b 00:11:22:33:44:55 -c 0 -q &
taskset -c 2 mausezahn vx0 -a own -b 00:11:22:33:44:55 -c 0 -q &