[PATCH 5.4 50/87] tcp: Fix data-races around sysctl_tcp_slow_start_after_idle.

[Greg Kroah-Hartman]

From: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>

[ Upstream commit 4845b5713ab18a1bb6e31d1fbb4d600240b8b691 ]

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

Fixes: 35089bb203f4 ("[TCP]: Add tcp_slow_start_after_idle sysctl.")
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/net/tcp.h     | 4 ++--
 net/ipv4/tcp_output.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index eb984ec22f22..aaf1d5d5a13b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1373,8 +1373,8 @@ static inline void tcp_slow_start_after_idle_check(struct sock *sk)
 	struct tcp_sock *tp = tcp_sk(sk);
 	s32 delta;
 
-	if (!sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle || tp->packets_out ||
-	    ca_ops->cong_control)
+	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle) ||
+	    tp->packets_out || ca_ops->cong_control)
 		return;
 	delta = tcp_jiffies32 - tp->lsndtime;
 	if (delta > inet_csk(sk)->icsk_rto)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 72ee1fca0501..5d9a1a498a18 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1673,7 +1673,7 @@ static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
 		if (tp->packets_out > tp->snd_cwnd_used)
 			tp->snd_cwnd_used = tp->packets_out;
 
-		if (sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle &&
+		if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle) &&
 		    (s32)(tcp_jiffies32 - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto &&
 		    !ca_ops->cong_control)
 			tcp_cwnd_application_limited(sk);
-- 
2.35.1