[PATCH v6 20/21] net/tcp: Add static_key for TCP-AO

[Dmitry Safonov <dima@arista.com>]

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>
---
 include/net/tcp.h    |  3 +++
 include/net/tcp_ao.h |  2 ++
 net/ipv4/tcp_ao.c    | 23 +++++++++++++++++++++++
 net/ipv4/tcp_input.c | 42 ++++++++++++++++++++++++++++--------------
 4 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index e7b077805d9e..8eae8e82980f 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2575,6 +2575,9 @@ 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)
diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h
index d1dcda8f81be..c19c9416ff6d 100644
--- a/include/net/tcp_ao.h
+++ b/include/net/tcp_ao.h
@@ -138,6 +138,8 @@ 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;
diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
index 40b13fcb0723..3538321a742f 100644
--- a/net/ipv4/tcp_ao.c
+++ b/net/ipv4/tcp_ao.c
@@ -17,6 +17,9 @@
 #include <net/ipv6.h>
 #include <net/icmp.h>
 
+DEFINE_STATIC_KEY_DEFERRED_FALSE(tcp_ao_needed, HZ);
+EXPORT_SYMBOL_GPL(tcp_ao_needed);
+
 int tcp_ao_calc_traffic_key(struct tcp_ao_key *mkt, u8 *key, void *ctx,
 			    unsigned int len)
 {
@@ -58,6 +61,9 @@ bool tcp_ao_ignore_icmp(struct sock *sk, int type, int code)
 	struct tcp_ao_info *ao;
 	bool ignore_icmp = false;
 
+	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
@@ -198,6 +204,9 @@ 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)
@@ -292,6 +301,7 @@ 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)
@@ -1037,6 +1047,11 @@ 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);
 
@@ -1443,6 +1458,10 @@ 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);
 	}
@@ -1705,6 +1724,10 @@ 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);
 	}
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d87c73346e8c..7f6f9b04e9e9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3524,17 +3524,14 @@ static inline bool tcp_may_update_window(const struct tcp_sock *tp,
 		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
 }
 
-/* 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) {
@@ -3543,20 +3540,27 @@ static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
 		ao->snd_sne_seq = ack;
 	}
 #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;
 }
 
-/* If we update tp->rcv_nxt, also update tp->bytes_received */
-static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
+static void tcp_rcv_sne_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
+	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) {
@@ -3565,6 +3569,16 @@ static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
 		ao->rcv_sne_seq = seq;
 	}
 #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;
+
+	sock_owned_by_me((struct sock *)tp);
+	tp->bytes_received += delta;
+	tcp_rcv_sne_update(tp, seq);
 	WRITE_ONCE(tp->rcv_nxt, seq);
 }
 
-- 
2.40.0