[PATCH net v2] wireguard: receive: annotate data-race around receiving_counter.counter

Syzkaller with KCSAN identified a data-race issue [1] when accessing
keypair->receiving_counter.counter.

This patch uses READ_ONCE() and WRITE_ONCE() annotations to fix the
problem.

[1]
BUG: KCSAN: data-race in wg_packet_decrypt_worker / wg_packet_rx_poll

write to 0xffff888107765888 of 8 bytes by interrupt on cpu 0:
 counter_validate drivers/net/wireguard/receive.c:321 [inline]
 wg_packet_rx_poll+0x3ac/0xf00 drivers/net/wireguard/receive.c:461
 __napi_poll+0x60/0x3b0 net/core/dev.c:6536
 napi_poll net/core/dev.c:6605 [inline]
 net_rx_action+0x32b/0x750 net/core/dev.c:6738
 __do_softirq+0xc4/0x279 kernel/softirq.c:553
 do_softirq+0x5e/0x90 kernel/softirq.c:454
 __local_bh_enable_ip+0x64/0x70 kernel/softirq.c:381
 __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline]
 _raw_spin_unlock_bh+0x36/0x40 kernel/locking/spinlock.c:210
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 ptr_ring_consume_bh include/linux/ptr_ring.h:367 [inline]
 wg_packet_decrypt_worker+0x6c5/0x700 drivers/net/wireguard/receive.c:499
 process_one_work kernel/workqueue.c:2633 [inline]
 ...

read to 0xffff888107765888 of 8 bytes by task 3196 on cpu 1:
 decrypt_packet drivers/net/wireguard/receive.c:252 [inline]
 wg_packet_decrypt_worker+0x220/0x700 drivers/net/wireguard/receive.c:501
 process_one_work kernel/workqueue.c:2633 [inline]
 process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2706
 worker_thread+0x525/0x730 kernel/workqueue.c:2787
 ...

Fixes: a9e90d9931f3 ("wireguard: noise: separate receive counter from send counter")
Reported-by: syzbot+d1de830e4ecdaac83d89@syzkaller.appspotmail.com
Signed-off-by: Nikita Zhandarovich <redacted>
---
v2: add missing annotation in wg_packet_rx_poll() per Eric Duzamet's
[off-list ref] helpful suggestion.

 drivers/net/wireguard/receive.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireguard/receive.c b/drivers/net/wireguard/receive.c
index a176653c8861..db01ec03bda0 100644
--- a/drivers/net/wireguard/receive.c
+++ b/drivers/net/wireguard/receive.c

@@ -251,7 +251,7 @@ static bool decrypt_packet(struct sk_buff *skb, struct noise_keypair *keypair)
 
 	if (unlikely(!READ_ONCE(keypair->receiving.is_valid) ||
 		  wg_birthdate_has_expired(keypair->receiving.birthdate, REJECT_AFTER_TIME) ||
-		  keypair->receiving_counter.counter >= REJECT_AFTER_MESSAGES)) {
+		  READ_ONCE(keypair->receiving_counter.counter) >= REJECT_AFTER_MESSAGES)) {
 		WRITE_ONCE(keypair->receiving.is_valid, false);
 		return false;
 	}

@@ -318,7 +318,7 @@ static bool counter_validate(struct noise_replay_counter *counter, u64 their_cou
 		for (i = 1; i <= top; ++i)
 			counter->backtrack[(i + index_current) &
 				((COUNTER_BITS_TOTAL / BITS_PER_LONG) - 1)] = 0;
-		counter->counter = their_counter;
+		WRITE_ONCE(counter->counter, their_counter);
 	}
 
 	index &= (COUNTER_BITS_TOTAL / BITS_PER_LONG) - 1;

@@ -463,7 +463,7 @@ int wg_packet_rx_poll(struct napi_struct *napi, int budget)
 			net_dbg_ratelimited("%s: Packet has invalid nonce %llu (max %llu)\n",
 					    peer->device->dev->name,
 					    PACKET_CB(skb)->nonce,
-					    keypair->receiving_counter.counter);
+					    READ_ONCE(keypair->receiving_counter.counter));
 			goto next;
 		}