tcp: Fix data-races around sysctl_tcp_dsack.

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

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_input.c b/net/ipv4/tcp_input.c
index 07dbcbae7782880baaf5fbca1d344170aa032c12..6fdad9505396a1bfe982b157cdfc8d03de74797f 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4426,7 +4426,7 @@ static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
 {
        struct tcp_sock *tp = tcp_sk(sk);
 
-       if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
+       if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
                int mib_idx;
 
                if (before(seq, tp->rcv_nxt))
@@ -4473,7 +4473,7 @@ static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
                NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
                tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
 
-               if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
+               if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
                        u32 end_seq = TCP_SKB_CB(skb)->end_seq;
 
                        tcp_rcv_spurious_retrans(sk, skb);