tcp: Fix a data-race around sysctl_tcp_comp_sack_nr.

[ 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@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7b59386..a33e6aa 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5491,7 +5491,7 @@ send_now:
        }
 
        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) {