1 files changed, 29 insertions, 9 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 36f195fb576a..e460ea7f767b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -494,15 +494,16 @@ static inline void tcp_synq_overflow(const struct sock *sk)
 		reuse = rcu_dereference(sk->sk_reuseport_cb);
 		if (likely(reuse)) {
 			last_overflow = READ_ONCE(reuse->synq_overflow_ts);
-			if (time_after32(now, last_overflow + HZ))
+			if (!time_between32(now, last_overflow,
+					    last_overflow + HZ))
 				WRITE_ONCE(reuse->synq_overflow_ts, now);
 			return;
 		}
 	}
 
-	last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
-	if (time_after32(now, last_overflow + HZ))
-		tcp_sk(sk)->rx_opt.ts_recent_stamp = now;
+	last_overflow = READ_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp);
+	if (!time_between32(now, last_overflow, last_overflow + HZ))
+		WRITE_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp, now);
 }
 
 /* syncookies: no recent synqueue overflow on this listening socket? */
@@ -517,13 +518,23 @@ static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
 		reuse = rcu_dereference(sk->sk_reuseport_cb);
 		if (likely(reuse)) {
 			last_overflow = READ_ONCE(reuse->synq_overflow_ts);
-			return time_after32(now, last_overflow +
-					    TCP_SYNCOOKIE_VALID);
+			return !time_between32(now, last_overflow - HZ,
+					       last_overflow +
+					       TCP_SYNCOOKIE_VALID);
 		}
 	}
 
-	last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
-	return time_after32(now, last_overflow + TCP_SYNCOOKIE_VALID);
+	last_overflow = READ_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp);
+
+	/* If last_overflow <= jiffies <= last_overflow + TCP_SYNCOOKIE_VALID,
+	 * then we're under synflood. However, we have to use
+	 * 'last_overflow - HZ' as lower bound. That's because a concurrent
+	 * tcp_synq_overflow() could update .ts_recent_stamp after we read
+	 * jiffies but before we store .ts_recent_stamp into last_overflow,
+	 * which could lead to rejecting a valid syncookie.
+	 */
+	return !time_between32(now, last_overflow - HZ,
+			       last_overflow + TCP_SYNCOOKIE_VALID);
 }
 
 static inline u32 tcp_cookie_time(void)
@@ -1755,9 +1766,18 @@ static inline bool tcp_skb_is_last(const struct sock *sk,
 	return skb_queue_is_last(&sk->sk_write_queue, skb);
 }
 
+/**
+ * tcp_write_queue_empty - test if any payload (or FIN) is available in write queue
+ * @sk: socket
+ *
+ * Since the write queue can have a temporary empty skb in it,
+ * we must not use "return skb_queue_empty(&sk->sk_write_queue)"
+ */
 static inline bool tcp_write_queue_empty(const struct sock *sk)
 {
-	return skb_queue_empty(&sk->sk_write_queue);
+	const struct tcp_sock *tp = tcp_sk(sk);
+
+	return tp->write_seq == tp->snd_nxt;
 }
 
 static inline bool tcp_rtx_queue_empty(const struct sock *sk)