net/tcp: Add TCP-AO sign to outgoing packets

Using precalculated traffic keys, sign TCP segments as prescribed by
RFC5925. Per RFC, TCP header options are included in sign calculation:
"The TCP header, by default including options, and where the TCP
checksum and TCP-AO MAC fields are set to zero, all in network-
byte order." (5.1.3)

tcp_ao_hash_header() has exclude_options parameter to optionally exclude
TCP header from hash calculation, as described in RFC5925 (9.1), this is
needed for interaction with middleboxes that may change "some TCP
options". This is wired up to AO key flags and setsockopt() later.

Similarly to TCP-MD5 hash TCP segment fragments.

From this moment a user can start sending TCP-AO signed segments with
one of crypto ahash algorithms from supported by Linux kernel. It can
have a user-specified MAC length, to either save TCP option header space
or provide higher protection using a longer signature.
The inbound segments are not yet verified, TCP-AO option is ignored and
they are accepted.

Co-developed-by: Francesco Ruggeri <fruggeri@arista.com>
Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
Co-developed-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 64 insertions, 0 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index b72c46cf229b..96e83159f1be 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -195,6 +195,7 @@ static_assert((1 << ATO_BITS) > TCP_DELACK_MAX);
 #define TCPOPT_SACK             5       /* SACK Block */
 #define TCPOPT_TIMESTAMP	8	/* Better RTT estimations/PAWS */
 #define TCPOPT_MD5SIG		19	/* MD5 Signature (RFC2385) */
+#define TCPOPT_AO		29	/* Authentication Option (RFC5925) */
 #define TCPOPT_MPTCP		30	/* Multipath TCP (RFC6824) */
 #define TCPOPT_FASTOPEN		34	/* Fast open (RFC7413) */
 #define TCPOPT_EXP		254	/* Experimental */
@@ -2200,6 +2201,9 @@ struct tcp_sock_af_ops {
 	int (*ao_calc_key_sk)(struct tcp_ao_key *mkt, u8 *key,
 			      const struct sock *sk,
 			      __be32 sisn, __be32 disn, bool send);
+	int (*calc_ao_hash)(char *location, struct tcp_ao_key *ao,
+			    const struct sock *sk, const struct sk_buff *skb,
+			    const u8 *tkey, int hash_offset, u32 sne);
 #endif
 };
 
@@ -2253,6 +2257,66 @@ static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
 }
 #endif
 
+struct tcp_key {
+	union {
+		struct tcp_ao_key *ao_key;
+		struct tcp_md5sig_key *md5_key;
+	};
+	enum {
+		TCP_KEY_NONE = 0,
+		TCP_KEY_MD5,
+		TCP_KEY_AO,
+	} type;
+};
+
+static inline void tcp_get_current_key(const struct sock *sk,
+				       struct tcp_key *out)
+{
+#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;
+	}
+#endif
+#ifdef CONFIG_TCP_MD5SIG
+	if (static_branch_unlikely(&tcp_md5_needed.key) &&
+	    rcu_access_pointer(tp->md5sig_info)) {
+		out->md5_key = tp->af_specific->md5_lookup(sk, sk);
+		if (out->md5_key) {
+			out->type = TCP_KEY_MD5;
+			return;
+		}
+	}
+#endif
+	out->type = TCP_KEY_NONE;
+}
+
+static inline bool tcp_key_is_md5(const struct tcp_key *key)
+{
+#ifdef CONFIG_TCP_MD5SIG
+	if (static_branch_unlikely(&tcp_md5_needed.key) &&
+	    key->type == TCP_KEY_MD5)
+		return true;
+#endif
+	return false;
+}
+
+static inline bool tcp_key_is_ao(const struct tcp_key *key)
+{
+#ifdef CONFIG_TCP_AO
+	if (key->type == TCP_KEY_AO)
+		return true;
+#endif
+	return false;
+}
+
 int tcpv4_offload_init(void);
 
 void tcp_v4_init(void);