net: prevent load/store tearing on sk->sk_stamp

Add a couple of READ_ONCE() and WRITE_ONCE() to prevent
load-tearing and store-tearing in sock_read_timestamp()
and sock_write_timestamp()

This might prevent another KCSAN report.

Fixes: 3a0ed3e9 ("sock: Make sock->sk_stamp thread-safe")
Signed-off-by: NEric Dumazet <edumazet@google.com>
Cc: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: NDeepa Dinamani <deepa.kernel@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -2342,7 +2342,7 @@ static inline ktime_t sock_read_timestamp(struct sock *sk)
 
 	return kt;
 #else
-	return sk->sk_stamp;
+	return READ_ONCE(sk->sk_stamp);
 #endif
 }
 
@@ -2353,7 +2353,7 @@ static inline void sock_write_timestamp(struct sock *sk, ktime_t kt)
 	sk->sk_stamp = kt;
 	write_sequnlock(&sk->sk_stamp_seq);
 #else
-	sk->sk_stamp = kt;
+	WRITE_ONCE(sk->sk_stamp, kt);
 #endif
 }