tcp: annotate data-race around challenge_timestamp

stable inclusion
from stable-v4.19.258
commit 12f99f07a5f4d7ec8d72da6ee8ef66f048634f6a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5UQH4
CVE: NA

--------------------------------

[ Upstream commit 8c705212 ]

challenge_timestamp can be read an written by concurrent threads.

This was expected, but we need to annotate the race to avoid potential issues.

Following patch moves challenge_timestamp and challenge_count
to per-netns storage to provide better isolation.

Fixes: 354e4aa3 ("tcp: RFC 5961 5.2 Blind Data Injection Attack Mitigation")
Reported-by: Nsyzbot <syzkaller@googlegroups.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Acked-by: NNeal Cardwell <ncardwell@google.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

net/ipv4/tcp_input.c

@@ -3471,11 +3471,11 @@ 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) {
+	if (now != READ_ONCE(challenge_timestamp)) {
 		u32 ack_limit = READ_ONCE(net->ipv4.sysctl_tcp_challenge_ack_limit);
 		u32 half = (ack_limit + 1) >> 1;
 
-		challenge_timestamp = now;
+		WRITE_ONCE(challenge_timestamp, now);
 		WRITE_ONCE(challenge_count, half + prandom_u32_max(ack_limit));
 	}
 	count = READ_ONCE(challenge_count);