net_sched: sch_fq: prepare for TIME_WAIT sockets

TCP stack is not attaching skb to TIME_WAIT sockets yet,
but we would like to allow this in the future.

Add sk_listener_or_tw() helper to detect the three states
that FQ needs to take care.

Like NEW_SYN_RECV, TIME_WAIT are not full sockets and
do not contain sk->sk_pacing_status, sk->sk_pacing_rate.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Brian Vazquez <brianvv@google.com>
Link: https://patch.msgid.link/20241010174817.1543642-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/sock.h

@@ -2802,6 +2802,16 @@ static inline bool sk_listener(const struct sock *sk)
 	return (1 << sk->sk_state) & (TCPF_LISTEN | TCPF_NEW_SYN_RECV);
 }
 
+/* This helper checks if a socket is a LISTEN or NEW_SYN_RECV or TIME_WAIT
+ * TCP SYNACK messages can be attached to LISTEN or NEW_SYN_RECV (depending on SYNCOOKIE)
+ * TCP RST and ACK can be attached to TIME_WAIT.
+ */
+static inline bool sk_listener_or_tw(const struct sock *sk)
+{
+	return (1 << READ_ONCE(sk->sk_state)) &
+	       (TCPF_LISTEN | TCPF_NEW_SYN_RECV | TCPF_TIME_WAIT);
+}
+
 void sock_enable_timestamp(struct sock *sk, enum sock_flags flag);
 int sock_recv_errqueue(struct sock *sk, struct msghdr *msg, int len, int level,
 		       int type);

net/sched/sch_fq.c

@@ -362,8 +362,9 @@ static struct fq_flow *fq_classify(struct Qdisc *sch, struct sk_buff *skb,
 	 * 3) We do not want to rate limit them (eg SYNFLOOD attack),
 	 *    especially if the listener set SO_MAX_PACING_RATE
 	 * 4) We pretend they are orphaned
+	 * TCP can also associate TIME_WAIT sockets with RST or ACK packets.
 	 */
-	if (!sk || sk_listener(sk)) {
+	if (!sk || sk_listener_or_tw(sk)) {
 		unsigned long hash = skb_get_hash(skb) & q->orphan_mask;
 
 		/* By forcing low order bit to 1, we make sure to not