[PATCH v1 net 08/15] tcp: Fix data-races around sysctl_tcp_workaround_signed_windows.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

While reading sysctl_tcp_workaround_signed_windows, it can be changed
concurrently.  Thus, we need to add READ_ONCE() to its readers.

Fixes: 15d99e02baba ("[TCP]: sysctl to allow TCP window > 32767 sans wscale")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
CC: Rick Jones <rick.jones2@hp.com>
---
 net/ipv4/tcp_output.c | 4 ++--
 net/mptcp/options.c   | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c38e07b50639..88f7d51e6691 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -230,7 +230,7 @@ void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss,
 	 * which we interpret as a sign the remote TCP is not
 	 * misinterpreting the window field as a signed quantity.
 	 */
-	if (sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows)
+	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows))
 		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
 	else
 		(*rcv_wnd) = min_t(u32, space, U16_MAX);
@@ -285,7 +285,7 @@ static u16 tcp_select_window(struct sock *sk)
 	 * scaled window.
 	 */
 	if (!tp->rx_opt.rcv_wscale &&
-	    sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows)
+	    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows))
 		new_win = min(new_win, MAX_TCP_WINDOW);
 	else
 		new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index bd8f0f425be4..30d289044e71 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -1271,7 +1271,7 @@ static void mptcp_set_rwin(struct tcp_sock *tp, struct tcphdr *th)
 		if (unlikely(th->syn))
 			new_win = min(new_win, 65535U) << tp->rx_opt.rcv_wscale;
 		if (!tp->rx_opt.rcv_wscale &&
-		    sock_net(ssk)->ipv4.sysctl_tcp_workaround_signed_windows)
+		    READ_ONCE(sock_net(ssk)->ipv4.sysctl_tcp_workaround_signed_windows))
 			new_win = min(new_win, MAX_TCP_WINDOW);
 		else
 			new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
-- 
2.30.2