tcp: Fix a data-race around sysctl_tcp_tw_reuse.

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

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index da5a3c44c4fb70f1d3ecc596e694a86267f1c44a..d16e6e40f47ba4aee2b1a412c42d2f9791698e27 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -108,10 +108,10 @@ static u32 tcp_v4_init_ts_off(const struct net *net, const struct sk_buff *skb)
 
 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
 {
+       int reuse = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_tw_reuse);
        const struct inet_timewait_sock *tw = inet_twsk(sktw);
        const struct tcp_timewait_sock *tcptw = tcp_twsk(sktw);
        struct tcp_sock *tp = tcp_sk(sk);
-       int reuse = sock_net(sk)->ipv4.sysctl_tcp_tw_reuse;
 
        if (reuse == 2) {
                /* Still does not detect *everything* that goes through