tcp: Fix a data-race around sysctl_tcp_thin_linear_timeouts.

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

Fixes: 36e31b0af587 ("net: TCP thin linear timeouts")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index ec5277b..50bba37 100644 (file)
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -578,7 +578,7 @@ out_reset_timer:
         * linear-timeout retransmissions into a black hole
         */
        if (sk->sk_state == TCP_ESTABLISHED &&
-           (tp->thin_lto || net->ipv4.sysctl_tcp_thin_linear_timeouts) &&
+           (tp->thin_lto || READ_ONCE(net->ipv4.sysctl_tcp_thin_linear_timeouts)) &&
            tcp_stream_is_thin(tp) &&
            icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
                icsk->icsk_backoff = 0;