tcp: Fix a data-race around sysctl_tcp_comp_sack_delay_ns.

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

Fixes: 7364cd7c5be7 ("tcp: add tcp_comp_sack_delay_ns sysctl")
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 ff2e0d87aee4880087df1263e0b5e6fa3f274aea..813744180d87920a5e5c88c9550b00cdcebca8a3 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5542,7 +5542,8 @@ send_now:
        if (tp->srtt_us && tp->srtt_us < rtt)
                rtt = tp->srtt_us;
 
-       delay = min_t(unsigned long, sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns,
+       delay = min_t(unsigned long,
+                     READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns),
                      rtt * (NSEC_PER_USEC >> 3)/20);
        sock_hold(sk);
        hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay),