net/tcp: Add static_key for TCP-AO

Similarly to TCP-MD5, add a static key to TCP-AO that is patched out
when there are no keys on a machine and dynamically enabled with the
first setsockopt(TCP_AO) adds a key on any socket. The static key is as
well dynamically disabled later when the socket is destructed.

The lifetime of enabled static key here is the same as ao_info: it is
enabled on allocation, passed over from full socket to twsk and
destructed when ao_info is scheduled for destruction.

Signed-off-by: Dmitry Safonov <dima@arista.com>
Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -2288,14 +2288,18 @@ static inline void tcp_get_current_key(const struct sock *sk,
 #if defined(CONFIG_TCP_AO) || defined(CONFIG_TCP_MD5SIG)
 	const struct tcp_sock *tp = tcp_sk(sk);
 #endif
-#ifdef CONFIG_TCP_AO
-	struct tcp_ao_info *ao;
 
-	ao = rcu_dereference_protected(tp->ao_info, lockdep_sock_is_held(sk));
-	if (ao) {
-		out->ao_key = READ_ONCE(ao->current_key);
-		out->type = TCP_KEY_AO;
-		return;
+#ifdef CONFIG_TCP_AO
+	if (static_branch_unlikely(&tcp_ao_needed.key)) {
+		struct tcp_ao_info *ao;
+
+		ao = rcu_dereference_protected(tp->ao_info,
+					       lockdep_sock_is_held(sk));
+		if (ao) {
+			out->ao_key = READ_ONCE(ao->current_key);
+			out->type = TCP_KEY_AO;
+			return;
+		}
 	}
 #endif
 #ifdef CONFIG_TCP_MD5SIG
@@ -2324,7 +2328,8 @@ static inline bool tcp_key_is_md5(const struct tcp_key *key)
 static inline bool tcp_key_is_ao(const struct tcp_key *key)
 {
 #ifdef CONFIG_TCP_AO
-	if (key->type == TCP_KEY_AO)
+	if (static_branch_unlikely(&tcp_ao_needed.key) &&
+	    key->type == TCP_KEY_AO)
 		return true;
 #endif
 	return false;
@@ -2718,6 +2723,9 @@ static inline bool tcp_ao_required(struct sock *sk, const void *saddr,
 	struct tcp_ao_info *ao_info;
 	struct tcp_ao_key *ao_key;
 
+	if (!static_branch_unlikely(&tcp_ao_needed.key))
+		return false;
+
 	ao_info = rcu_dereference_check(tcp_sk(sk)->ao_info,
 					lockdep_sock_is_held(sk));
 	if (!ao_info)

include/net/tcp_ao.h

@@ -151,6 +151,8 @@ do {									\
 
 #ifdef CONFIG_TCP_AO
 /* TCP-AO structures and functions */
+#include <linux/jump_label.h>
+extern struct static_key_false_deferred tcp_ao_needed;
 
 struct tcp4_ao_context {
 	__be32		saddr;

net/ipv4/tcp_ao.c

@@ -17,6 +17,8 @@
 #include <net/ipv6.h>
 #include <net/icmp.h>
 
+DEFINE_STATIC_KEY_DEFERRED_FALSE(tcp_ao_needed, HZ);
+
 int tcp_ao_calc_traffic_key(struct tcp_ao_key *mkt, u8 *key, void *ctx,
 			    unsigned int len, struct tcp_sigpool *hp)
 {
@@ -50,6 +52,9 @@ bool tcp_ao_ignore_icmp(const struct sock *sk, int family, int type, int code)
 	bool ignore_icmp = false;
 	struct tcp_ao_info *ao;
 
+	if (!static_branch_unlikely(&tcp_ao_needed.key))
+		return false;
+
 	/* RFC5925, 7.8:
 	 * >> A TCP-AO implementation MUST default to ignore incoming ICMPv4
 	 * messages of Type 3 (destination unreachable), Codes 2-4 (protocol
@@ -185,6 +190,9 @@ static struct tcp_ao_key *__tcp_ao_do_lookup(const struct sock *sk,
 	struct tcp_ao_key *key;
 	struct tcp_ao_info *ao;
 
+	if (!static_branch_unlikely(&tcp_ao_needed.key))
+		return NULL;
+
 	ao = rcu_dereference_check(tcp_sk(sk)->ao_info,
 				   lockdep_sock_is_held(sk));
 	if (!ao)
@@ -276,6 +284,7 @@ void tcp_ao_destroy_sock(struct sock *sk, bool twsk)
 	}
 
 	kfree_rcu(ao, rcu);
+	static_branch_slow_dec_deferred(&tcp_ao_needed);
 }
 
 void tcp_ao_time_wait(struct tcp_timewait_sock *tcptw, struct tcp_sock *tp)
@@ -1180,6 +1189,11 @@ int tcp_ao_copy_all_matching(const struct sock *sk, struct sock *newsk,
 		goto free_and_exit;
 	}
 
+	if (!static_key_fast_inc_not_disabled(&tcp_ao_needed.key.key)) {
+		ret = -EUSERS;
+		goto free_and_exit;
+	}
+
 	key_head = rcu_dereference(hlist_first_rcu(&new_ao->head));
 	first_key = hlist_entry_safe(key_head, struct tcp_ao_key, node);
 
@@ -1607,6 +1621,10 @@ static int tcp_ao_add_cmd(struct sock *sk, unsigned short int family,
 
 	tcp_ao_link_mkt(ao_info, key);
 	if (first) {
+		if (!static_branch_inc(&tcp_ao_needed.key)) {
+			ret = -EUSERS;
+			goto err_free_sock;
+		}
 		sk_gso_disable(sk);
 		rcu_assign_pointer(tcp_sk(sk)->ao_info, ao_info);
 	}
@@ -1875,6 +1893,10 @@ static int tcp_ao_info_cmd(struct sock *sk, unsigned short int family,
 	if (new_rnext)
 		WRITE_ONCE(ao_info->rnext_key, new_rnext);
 	if (first) {
+		if (!static_branch_inc(&tcp_ao_needed.key)) {
+			err = -EUSERS;
+			goto out;
+		}
 		sk_gso_disable(sk);
 		rcu_assign_pointer(tcp_sk(sk)->ao_info, ao_info);
 	}

net/ipv4/tcp_input.c

@@ -3572,41 +3572,55 @@ static inline bool tcp_may_update_window(const struct tcp_sock *tp,
 		(ack_seq == tp->snd_wl1 && (nwin > tp->snd_wnd || !nwin));
 }
 
-/* If we update tp->snd_una, also update tp->bytes_acked */
-static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
+static void tcp_snd_sne_update(struct tcp_sock *tp, u32 ack)
 {
-	u32 delta = ack - tp->snd_una;
 #ifdef CONFIG_TCP_AO
 	struct tcp_ao_info *ao;
-#endif
 
-	sock_owned_by_me((struct sock *)tp);
-	tp->bytes_acked += delta;
-#ifdef CONFIG_TCP_AO
+	if (!static_branch_unlikely(&tcp_ao_needed.key))
+		return;
+
 	ao = rcu_dereference_protected(tp->ao_info,
 				       lockdep_sock_is_held((struct sock *)tp));
 	if (ao && ack < tp->snd_una)
 		ao->snd_sne++;
 #endif
+}
+
+/* If we update tp->snd_una, also update tp->bytes_acked */
+static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
+{
+	u32 delta = ack - tp->snd_una;
+
+	sock_owned_by_me((struct sock *)tp);
+	tp->bytes_acked += delta;
+	tcp_snd_sne_update(tp, ack);
 	tp->snd_una = ack;
 }
 
+static void tcp_rcv_sne_update(struct tcp_sock *tp, u32 seq)
+{
+#ifdef CONFIG_TCP_AO
+	struct tcp_ao_info *ao;
+
+	if (!static_branch_unlikely(&tcp_ao_needed.key))
+		return;
+
+	ao = rcu_dereference_protected(tp->ao_info,
+				       lockdep_sock_is_held((struct sock *)tp));
+	if (ao && seq < tp->rcv_nxt)
+		ao->rcv_sne++;
+#endif
+}
+
 /* If we update tp->rcv_nxt, also update tp->bytes_received */
 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
 {
 	u32 delta = seq - tp->rcv_nxt;
-#ifdef CONFIG_TCP_AO
-	struct tcp_ao_info *ao;
-#endif
 
 	sock_owned_by_me((struct sock *)tp);
 	tp->bytes_received += delta;
-#ifdef CONFIG_TCP_AO
-	ao = rcu_dereference_protected(tp->ao_info,
-				       lockdep_sock_is_held((struct sock *)tp));
-	if (ao && seq < tp->rcv_nxt)
-		ao->rcv_sne++;
-#endif
+	tcp_rcv_sne_update(tp, seq);
 	WRITE_ONCE(tp->rcv_nxt, seq);
 }
 

net/ipv4/tcp_ipv4.c

@@ -1024,18 +1024,20 @@ static void tcp_v4_timewait_ack(struct sock *sk, struct sk_buff *skb)
 #ifdef CONFIG_TCP_AO
 	struct tcp_ao_info *ao_info;
 
-	/* FIXME: the segment to-be-acked is not verified yet */
-	ao_info = rcu_dereference(tcptw->ao_info);
-	if (ao_info) {
-		const struct tcp_ao_hdr *aoh;
+	if (static_branch_unlikely(&tcp_ao_needed.key)) {
+		/* FIXME: the segment to-be-acked is not verified yet */
+		ao_info = rcu_dereference(tcptw->ao_info);
+		if (ao_info) {
+			const struct tcp_ao_hdr *aoh;
 
-		if (tcp_parse_auth_options(tcp_hdr(skb), NULL, &aoh)) {
-			inet_twsk_put(tw);
-			return;
+			if (tcp_parse_auth_options(tcp_hdr(skb), NULL, &aoh)) {
+				inet_twsk_put(tw);
+				return;
+			}
+
+			if (aoh)
+				key.ao_key = tcp_ao_established_key(ao_info, aoh->rnext_keyid, -1);
 		}
-
-		if (aoh)
-			key.ao_key = tcp_ao_established_key(ao_info, aoh->rnext_keyid, -1);
 	}
 	if (key.ao_key) {
 		struct tcp_ao_key *rnext_key;
@@ -1081,7 +1083,8 @@ static void tcp_v4_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
 					     tcp_sk(sk)->snd_nxt;
 
 #ifdef CONFIG_TCP_AO
-	if (tcp_rsk_used_ao(req)) {
+	if (static_branch_unlikely(&tcp_ao_needed.key) &&
+	    tcp_rsk_used_ao(req)) {
 		const union tcp_md5_addr *addr;
 		const struct tcp_ao_hdr *aoh;
 

net/ipv6/tcp_ipv6.c

@@ -1154,17 +1154,19 @@ static void tcp_v6_timewait_ack(struct sock *sk, struct sk_buff *skb)
 #ifdef CONFIG_TCP_AO
 	struct tcp_ao_info *ao_info;
 
-	/* FIXME: the segment to-be-acked is not verified yet */
-	ao_info = rcu_dereference(tcptw->ao_info);
-	if (ao_info) {
-		const struct tcp_ao_hdr *aoh;
+	if (static_branch_unlikely(&tcp_ao_needed.key)) {
 
-		/* Invalid TCP option size or twice included auth */
-		if (tcp_parse_auth_options(tcp_hdr(skb), NULL, &aoh))
-			goto out;
-		if (aoh) {
-			key.ao_key = tcp_ao_established_key(ao_info,
-							    aoh->rnext_keyid, -1);
+		/* FIXME: the segment to-be-acked is not verified yet */
+		ao_info = rcu_dereference(tcptw->ao_info);
+		if (ao_info) {
+			const struct tcp_ao_hdr *aoh;
+
+			/* Invalid TCP option size or twice included auth */
+			if (tcp_parse_auth_options(tcp_hdr(skb), NULL, &aoh))
+				goto out;
+			if (aoh)
+				key.ao_key = tcp_ao_established_key(ao_info,
+						aoh->rnext_keyid, -1);
 		}
 	}
 	if (key.ao_key) {
@@ -1206,7 +1208,8 @@ static void tcp_v6_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
 	struct tcp_key key = {};
 
 #ifdef CONFIG_TCP_AO
-	if (tcp_rsk_used_ao(req)) {
+	if (static_branch_unlikely(&tcp_ao_needed.key) &&
+	    tcp_rsk_used_ao(req)) {
 		const struct in6_addr *addr = &ipv6_hdr(skb)->saddr;
 		const struct tcp_ao_hdr *aoh;
 		int l3index;