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

[Nikita Zhandarovich]

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

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

Fixes: a9e90d9931f3 ("wireguard: noise: separate receive counter from send counter")
Reported-by: syzbot+d1de830e4ecdaac83d89@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>
---
 drivers/net/wireguard/receive.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireguard/receive.c b/drivers/net/wireguard/receive.c
index 0b3f0c843550..b5232ffa8bc7 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;
-- 
2.25.1