[PATCH] tcp: use WRITE_ONCE() for tsoffset in tcp_v6_connect()

[Wesley Atwell]

Commit dd23c9f1e8d5 ("tcp: annotate data-races around tp->tsoffset")
updated do_tcp_getsockopt() to read tp->tsoffset with READ_ONCE()
for TCP_TIMESTAMP because another CPU may change it concurrently.

tcp_v6_connect() still stores tp->tsoffset with a plain write. That
store runs under lock_sock() via inet_stream_connect(), but the socket
lock does not serialize a concurrent getsockopt(TCP_TIMESTAMP) from
another task sharing the socket.

Use WRITE_ONCE() for the tcp_v6_connect() store so the connect-time
writer matches the lockless TCP_TIMESTAMP reader. This also makes the
IPv6 path consistent with tcp_v4_connect().

Signed-off-by: Wesley Atwell <atwellwea@xxxxxxxxx>
---
 net/ipv6/tcp_ipv6.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index bb09d5ccf599..ba7cd7d3d4da 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -325,7 +325,7 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr_unsized *uaddr,
 						 inet->inet_dport);
 		if (!tp->write_seq)
 			WRITE_ONCE(tp->write_seq, st.seq);
-		tp->tsoffset = st.ts_off;
+		WRITE_ONCE(tp->tsoffset, st.ts_off);
 	}
 
 	if (tcp_fastopen_defer_connect(sk, &err))
-- 
2.34.1