net/tcp: Verify inbound TCP-AO signed segments

Now there is a common function to verify signature on TCP segments:
tcp_inbound_hash(). It has checks for all possible cross-interactions
with MD5 signs as well as with unsigned segments.

The rules from RFC5925 are:
(1) Any TCP segment can have at max only one signature.
(2) TCP connections can't switch between using TCP-MD5 and TCP-AO.
(3) TCP-AO connections can't stop using AO, as well as unsigned
    connections can't suddenly start using AO.

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, 51 insertions, 2 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index c7f80cc94d718..8e1f835bad227 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1809,7 +1809,7 @@ tcp_md5_do_lookup_any_l3index(const struct sock *sk,
 enum skb_drop_reason
 tcp_inbound_md5_hash(const struct sock *sk, const struct sk_buff *skb,
 		     const void *saddr, const void *daddr,
-		     int family, int dif, int sdif);
+		     int family, int l3index, const __u8 *hash_location);
 
 
 #define tcp_twsk_md5_key(twsk)	((twsk)->tw_md5_key)
@@ -1831,7 +1831,7 @@ tcp_md5_do_lookup_any_l3index(const struct sock *sk,
 static inline enum skb_drop_reason
 tcp_inbound_md5_hash(const struct sock *sk, const struct sk_buff *skb,
 		     const void *saddr, const void *daddr,
-		     int family, int dif, int sdif)
+		     int family, int l3index, const __u8 *hash_location)
 {
 	return SKB_NOT_DROPPED_YET;
 }
@@ -2730,4 +2730,53 @@ static inline bool tcp_ao_required(struct sock *sk, const void *saddr,
 	return false;
 }
 
+/* Called with rcu_read_lock() */
+static inline enum skb_drop_reason
+tcp_inbound_hash(struct sock *sk, const struct request_sock *req,
+		 const struct sk_buff *skb,
+		 const void *saddr, const void *daddr,
+		 int family, int dif, int sdif)
+{
+	const struct tcphdr *th = tcp_hdr(skb);
+	const struct tcp_ao_hdr *aoh;
+	const __u8 *md5_location;
+	int l3index;
+
+	/* Invalid option or two times meet any of auth options */
+	if (tcp_parse_auth_options(th, &md5_location, &aoh))
+		return SKB_DROP_REASON_TCP_AUTH_HDR;
+
+	if (req) {
+		if (tcp_rsk_used_ao(req) != !!aoh)
+			return SKB_DROP_REASON_TCP_AOFAILURE;
+	}
+
+	/* sdif set, means packet ingressed via a device
+	 * in an L3 domain and dif is set to the l3mdev
+	 */
+	l3index = sdif ? dif : 0;
+
+	/* Fast path: unsigned segments */
+	if (likely(!md5_location && !aoh)) {
+		/* Drop if there's TCP-MD5 or TCP-AO key with any rcvid/sndid
+		 * for the remote peer. On TCP-AO established connection
+		 * the last key is impossible to remove, so there's
+		 * always at least one current_key.
+		 */
+		if (tcp_ao_required(sk, saddr, family))
+			return SKB_DROP_REASON_TCP_AONOTFOUND;
+		if (unlikely(tcp_md5_do_lookup(sk, l3index, saddr, family))) {
+			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND);
+			return SKB_DROP_REASON_TCP_MD5NOTFOUND;
+		}
+		return SKB_NOT_DROPPED_YET;
+	}
+
+	if (aoh)
+		return tcp_inbound_ao_hash(sk, skb, family, req, aoh);
+
+	return tcp_inbound_md5_hash(sk, skb, saddr, daddr, family,
+				    l3index, md5_location);
+}
+
 #endif	/* _TCP_H */