KCSAN reports a race in the CPU round robin function, which, as the comment points out, is intentional:

BUG: KCSAN: data-race in wg_packet_send_staged_packets / wg_packet_send_staged_packets

read to 0xffff88811254eb28 of 4 bytes by task 3160 on cpu 1: wg_cpumask_next_online drivers/net/wireguard/queueing.h:127 [inline] wg_queue_enqueue_per_device_and_peer drivers/net/wireguard/queueing.h:173 [inline] wg_packet_create_data drivers/net/wireguard/send.c:320 [inline] wg_packet_send_staged_packets+0x60e/0xac0 drivers/net/wireguard/send.c:388 wg_packet_send_keepalive+0xe2/0x100 drivers/net/wireguard/send.c:239 wg_receive_handshake_packet drivers/net/wireguard/receive.c:186 [inline] wg_packet_handshake_receive_worker+0x449/0x5f0 drivers/net/wireguard/receive.c:213 process_one_work kernel/workqueue.c:3248 [inline] process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3329 worker_thread+0x526/0x720 kernel/workqueue.c:3409 kthread+0x1d1/0x210 kernel/kthread.c:389 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

write to 0xffff88811254eb28 of 4 bytes by task 3158 on cpu 0: wg_cpumask_next_online drivers/net/wireguard/queueing.h:130 [inline] wg_queue_enqueue_per_device_and_peer drivers/net/wireguard/queueing.h:173 [inline] wg_packet_create_data drivers/net/wireguard/send.c:320 [inline] wg_packet_send_staged_packets+0x6e5/0xac0 drivers/net/wireguard/send.c:388 wg_packet_send_keepalive+0xe2/0x100 drivers/net/wireguard/send.c:239 wg_receive_handshake_packet drivers/net/wireguard/receive.c:186 [inline] wg_packet_handshake_receive_worker+0x449/0x5f0 drivers/net/wireguard/receive.c:213 process_one_work kernel/workqueue.c:3248 [inline] process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3329 worker_thread+0x526/0x720 kernel/workqueue.c:3409 kthread+0x1d1/0x210 kernel/kthread.c:389 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

value changed: 0xffffffff -> 0x00000000

Mark this race as intentional by using READ/WRITE_ONCE().

Cc: stable@vger.kernel.org Fixes: e7096c131e51 ("net: WireGuard secure network tunnel") Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com --- drivers/net/wireguard/queueing.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireguard/queueing.h b/drivers/net/wireguard/queueing.h index 1ea4f874e367..7eb76724b3ed 100644 --- a/drivers/net/wireguard/queueing.h +++ b/drivers/net/wireguard/queueing.h @@ -124,10 +124,10 @@ static inline int wg_cpumask_choose_online(int *stored_cpu, unsigned int id) */ static inline int wg_cpumask_next_online(int *last_cpu) { - int cpu = cpumask_next(*last_cpu, cpu_online_mask); + int cpu = cpumask_next(READ_ONCE(*last_cpu), cpu_online_mask); if (cpu >= nr_cpu_ids) cpu = cpumask_first(cpu_online_mask); - *last_cpu = cpu; + WRITE_ONCE(*last_cpu, cpu); return cpu; }