tcp: Fix a data-race around sysctl_tcp_challenge_ack_limit.

commit db3815a2fa691da145cfbe834584f31ad75df9ff upstream.

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

Fixes: 282f23c6ee34 ("tcp: implement RFC 5961 3.2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 426f8fe..a5357eb 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3622,7 +3622,7 @@ static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
        /* Then check host-wide RFC 5961 rate limit. */
        now = jiffies / HZ;
        if (now != challenge_timestamp) {
-               u32 ack_limit = net->ipv4.sysctl_tcp_challenge_ack_limit;
+               u32 ack_limit = READ_ONCE(net->ipv4.sysctl_tcp_challenge_ack_limit);
                u32 half = (ack_limit + 1) >> 1;
 
                challenge_timestamp = now;