tcp: Fix data-races around sysctl_tcp_syn(ack)?_retries.

While reading sysctl_tcp_syn(ack)?_retries, they can be changed
concurrently.  Thus, we need to add READ_ONCE() to their 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/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 2c44556..eb31c71 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -833,7 +833,8 @@ static void reqsk_timer_handler(struct timer_list *t)
 
        icsk = inet_csk(sk_listener);
        net = sock_net(sk_listener);
-       max_syn_ack_retries = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_synack_retries;
+       max_syn_ack_retries = icsk->icsk_syn_retries ? :
+               READ_ONCE(net->ipv4.sysctl_tcp_synack_retries);
        /* Normally all the openreqs are young and become mature
         * (i.e. converted to established socket) for first timeout.
         * If synack was not acknowledged for 1 second, it means

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 2222dfd..19ce08c 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3967,7 +3967,8 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
                val = keepalive_probes(tp);
                break;
        case TCP_SYNCNT:
-               val = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
+               val = icsk->icsk_syn_retries ? :
+                       READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);
                break;
        case TCP_LINGER2:
                val = tp->linger2;

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 4f3b9ab..a234704 100644 (file)
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -239,7 +239,8 @@ static int tcp_write_timeout(struct sock *sk)
        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
                if (icsk->icsk_retransmits)
                        __dst_negative_advice(sk);
-               retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
+               retry_until = icsk->icsk_syn_retries ? :
+                       READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);
                expired = icsk->icsk_retransmits >= retry_until;
        } else {
                if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0)) {
@@ -406,12 +407,15 @@ abort:            tcp_write_err(sk);
 static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
 {
        struct inet_connection_sock *icsk = inet_csk(sk);
-       int max_retries = icsk->icsk_syn_retries ? :
-           sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
        struct tcp_sock *tp = tcp_sk(sk);
+       int max_retries;
 
        req->rsk_ops->syn_ack_timeout(req);
 
+       /* add one more retry for fastopen */
+       max_retries = icsk->icsk_syn_retries ? :
+               READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1;
+
        if (req->num_timeout >= max_retries) {
                tcp_write_err(sk);
                return;