tcp: Fix a data-race around sysctl_tcp_comp_sack_delay_ns.

[ Upstream commit 4866b2b0f7672b6d760c4b8ece6fb56f965dcc8a ] While reading sysctl_tcp_comp_sack_delay_ns, it can be changed concurrently. Thus, we need to add READ_ONCE() to its reader. Fixes: 6d82aa2 ("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> Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: q2ven

net/ipv4/tcp_input.c

@@ -5512,7 +5512,8 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
 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),