tcp: Fix a data-race around sysctl_tcp_ecn_fallback.

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

Fixes: d444f4d90464 ("tcp: add rfc3168, section 6.1.1.1. fallback")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 5e308c1715afc617f7bb821182ccc2176ed26e65..108fd86f2718d6124017aaee8f640a4df54d5529 100644 (file)
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -685,6 +685,8 @@ static struct ctl_table ipv4_net_table[] = {
                .maxlen         = sizeof(u8),
                .mode           = 0644,
                .proc_handler   = proc_dou8vec_minmax,
+               .extra1         = SYSCTL_ZERO,
+               .extra2         = SYSCTL_ONE,
        },
        {
                .procname       = "ip_dynaddr",

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3dc17551ce25652e1fe2c305df4c0e31e4425a1e..11aa0ab10bbad17142b06baa7eecd7d569b33131 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -346,7 +346,7 @@ static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
 
 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
 {
-       if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
+       if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback))
                /* tp->ecn_flags are cleared at a later point in time when
                 * SYN ACK is ultimatively being received.
                 */