[PATCH 4.19 20/32] tcp: Fix a data-race around sysctl_tcp_comp_sack_nr.

[Greg Kroah-Hartman]

From: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>

[ Upstream commit 79f55473bfc8ac51bd6572929a679eeb4da22251 ]

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

Fixes: 9c21d2fc41c0 ("tcp: add tcp_comp_sack_nr sysctl")
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index b71866aba426..e1d065ea5a15 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5239,7 +5239,7 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
 	}
 
 	if (!tcp_is_sack(tp) ||
-	    tp->compressed_ack >= sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr)
+	    tp->compressed_ack >= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr))
 		goto send_now;
 
 	if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
-- 
2.35.1