net/tcp: Don't consider TCP_CLOSE in TCP_AO_ESTABLISHED

TCP_CLOSE may or may not have current/rnext keys and should not be
considered "established". The fast-path for TCP_CLOSE is
SKB_DROP_REASON_TCP_CLOSE. This is what tcp_rcv_state_process() does
anyways. Add an early drop path to not spend any time verifying
segment signatures for sockets in TCP_CLOSE state.

Cc: stable@vger.kernel.org # v6.7
Fixes: 0a3a809 ("net/tcp: Verify inbound TCP-AO signed segments")
Signed-off-by: Dmitry Safonov <0x7f454c46@gmail.com>
Link: https://lore.kernel.org/r/20240529-tcp_ao-sk_state-v1-1-d69b5d323c52@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/tcp_ao.h

@@ -86,7 +86,8 @@ static inline int tcp_ao_sizeof_key(const struct tcp_ao_key *key)
 struct tcp_ao_info {
 	/* List of tcp_ao_key's */
 	struct hlist_head	head;
-	/* current_key and rnext_key aren't maintained on listen sockets.
+	/* current_key and rnext_key are maintained on sockets
+	 * in TCP_AO_ESTABLISHED states.
 	 * Their purpose is to cache keys on established connections,
 	 * saving needless lookups. Never dereference any of them from
 	 * listen sockets.
@@ -201,9 +202,9 @@ struct tcp6_ao_context {
 };
 
 struct tcp_sigpool;
+/* Established states are fast-path and there always is current_key/rnext_key */
 #define TCP_AO_ESTABLISHED (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_FIN_WAIT2 | \
-			    TCPF_CLOSE | TCPF_CLOSE_WAIT | \
-			    TCPF_LAST_ACK | TCPF_CLOSING)
+			    TCPF_CLOSE_WAIT | TCPF_LAST_ACK | TCPF_CLOSING)
 
 int tcp_ao_transmit_skb(struct sock *sk, struct sk_buff *skb,
 			struct tcp_ao_key *key, struct tcphdr *th,

net/ipv4/tcp_ao.c

@@ -933,6 +933,7 @@ tcp_inbound_ao_hash(struct sock *sk, const struct sk_buff *skb,
 	struct tcp_ao_key *key;
 	__be32 sisn, disn;
 	u8 *traffic_key;
+	int state;
 	u32 sne = 0;
 
 	info = rcu_dereference(tcp_sk(sk)->ao_info);
@@ -948,8 +949,9 @@ tcp_inbound_ao_hash(struct sock *sk, const struct sk_buff *skb,
 		disn = 0;
 	}
 
+	state = READ_ONCE(sk->sk_state);
 	/* Fast-path */
-	if (likely((1 << sk->sk_state) & TCP_AO_ESTABLISHED)) {
+	if (likely((1 << state) & TCP_AO_ESTABLISHED)) {
 		enum skb_drop_reason err;
 		struct tcp_ao_key *current_key;
 
@@ -988,6 +990,9 @@ tcp_inbound_ao_hash(struct sock *sk, const struct sk_buff *skb,
 		return SKB_NOT_DROPPED_YET;
 	}
 
+	if (unlikely(state == TCP_CLOSE))
+		return SKB_DROP_REASON_TCP_CLOSE;
+
 	/* Lookup key based on peer address and keyid.
 	 * current_key and rnext_key must not be used on tcp listen
 	 * sockets as otherwise:
@@ -1001,7 +1006,7 @@ tcp_inbound_ao_hash(struct sock *sk, const struct sk_buff *skb,
 	if (th->syn && !th->ack)
 		goto verify_hash;
 
-	if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_NEW_SYN_RECV)) {
+	if ((1 << state) & (TCPF_LISTEN | TCPF_NEW_SYN_RECV)) {
 		/* Make the initial syn the likely case here */
 		if (unlikely(req)) {
 			sne = tcp_ao_compute_sne(0, tcp_rsk(req)->rcv_isn,
@@ -1018,14 +1023,14 @@ tcp_inbound_ao_hash(struct sock *sk, const struct sk_buff *skb,
 			/* no way to figure out initial sisn/disn - drop */
 			return SKB_DROP_REASON_TCP_FLAGS;
 		}
-	} else if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
+	} else if ((1 << state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 		disn = info->lisn;
 		if (th->syn || th->rst)
 			sisn = th->seq;
 		else
 			sisn = info->risn;
 	} else {
-		WARN_ONCE(1, "TCP-AO: Unexpected sk_state %d", sk->sk_state);
+		WARN_ONCE(1, "TCP-AO: Unexpected sk_state %d", state);
 		return SKB_DROP_REASON_TCP_AOFAILURE;
 	}
 verify_hash: