Babel: Add MAC authentication support

This implements support for MAC authentication in the Babel protocol, as
specified by RFC 8967. The implementation seeks to follow the RFC as close
as possible, with the only deliberate deviation being the addition of
support for all the HMAC algorithms already supported by Bird, as well as
the Blake2b variant of the Blake algorithm.

For description of applicability, assumptions and security properties,
see RFC 8967 sections 1.1 and 1.2.

1 files changed, 59 insertions, 7 deletions

diff --git a/proto/babel/babel.h b/proto/babel/babel.h
index 09bf530c..ef5b4a5d 100644
--- a/proto/babel/babel.h
+++ b/proto/babel/babel.h
@@ -19,6 +19,7 @@
 #include "nest/route.h"
 #include "nest/protocol.h"
 #include "nest/locks.h"
+#include "nest/password.h"
 #include "lib/resource.h"
 #include "lib/lists.h"
 #include "lib/socket.h"
@@ -60,6 +61,14 @@
 #define BABEL_OVERHEAD		(IP6_HEADER_LENGTH+UDP_HEADER_LENGTH)
 #define BABEL_MIN_MTU		(512 + BABEL_OVERHEAD)
 
+#define BABEL_AUTH_NONE		0
+#define BABEL_AUTH_MAC			1
+#define BABEL_AUTH_NONCE_LEN		10	/* we send 80 bit nonces */
+#define BABEL_AUTH_MAX_NONCE_LEN	192	/* max allowed by spec */
+#define BABEL_AUTH_INDEX_LEN		32	/* max size in spec */
+#define BABEL_AUTH_NEIGHBOR_TIMEOUT	(300 S_)
+#define BABEL_AUTH_CHALLENGE_TIMEOUT	(30 S_)
+#define BABEL_AUTH_CHALLENGE_INTERVAL	(300 MS_) /* used for both challenges and replies */
 
 enum babel_tlv_type {
   BABEL_TLV_PAD1		= 0,
@@ -73,13 +82,10 @@ enum babel_tlv_type {
   BABEL_TLV_UPDATE		= 8,
   BABEL_TLV_ROUTE_REQUEST	= 9,
   BABEL_TLV_SEQNO_REQUEST	= 10,
-  /* extensions - not implemented
-  BABEL_TLV_TS_PC		= 11,
-  BABEL_TLV_HMAC		= 12,
-  BABEL_TLV_SS_UPDATE		= 13,
-  BABEL_TLV_SS_REQUEST		= 14,
-  BABEL_TLV_SS_SEQNO_REQUEST	= 15,
-  */
+  BABEL_TLV_MAC		= 16,
+  BABEL_TLV_PC			= 17,
+  BABEL_TLV_CHALLENGE_REQ	= 18,
+  BABEL_TLV_CHALLENGE_REPLY	= 19,
   BABEL_TLV_MAX
 };
 
@@ -137,6 +143,12 @@ struct babel_iface_config {
 
   ip_addr next_hop_ip4;
   ip_addr next_hop_ip6;
+
+  u8 auth_type;			/* Authentication type (BABEL_AUTH_*) */
+  u8 auth_permissive;			/* Don't drop packets failing auth check */
+  uint mac_num_keys;			/* Number of configured HMAC keys */
+  uint mac_total_len;			/* Total digest length for all configured keys */
+  list *passwords;			/* Passwords for authentication */
 };
 
 struct babel_proto {
@@ -184,6 +196,10 @@ struct babel_iface {
 
   u16 hello_seqno;			/* To be increased on each hello */
 
+  u32 auth_pc;
+  int auth_tx_overhead;
+  u8 auth_index[BABEL_AUTH_INDEX_LEN];
+
   btime next_hello;
   btime next_regular;
   btime next_triggered;
@@ -206,9 +222,20 @@ struct babel_neighbor {
   u16 hello_map;
   u16 next_hello_seqno;
   uint last_hello_int;
+
+  u32 auth_pc;
+  u8 auth_passed;
+  u8 auth_index_len;
+  u8 auth_index[BABEL_AUTH_INDEX_LEN];
+  u8 auth_nonce[BABEL_AUTH_NONCE_LEN];
+  btime auth_nonce_expiry;
+  btime auth_next_challenge;
+  btime auth_next_challenge_reply;
+
   /* expiry timers */
   btime hello_expiry;
   btime ihu_expiry;
+  btime auth_expiry;
 
   list routes;				/* Routes this neighbour has sent us (struct babel_route) */
   list requests;			/* Seqno requests bound to this neighbor */
@@ -340,6 +367,12 @@ struct babel_msg_seqno_request {
   ip_addr sender;
 };
 
+struct babel_msg_challenge {
+  u8 type;
+  u8 nonce_len;
+  u8 *nonce;
+};
+
 union babel_msg {
   u8 type;
   struct babel_msg_ack_req ack_req;
@@ -349,6 +382,7 @@ union babel_msg {
   struct babel_msg_update update;
   struct babel_msg_route_request route_request;
   struct babel_msg_seqno_request seqno_request;
+  struct babel_msg_challenge challenge;
 };
 
 struct babel_msg_node {
@@ -356,6 +390,20 @@ struct babel_msg_node {
   union babel_msg msg;
 };
 
+/* only used for auth checking, so not a part of union above */
+struct babel_msg_auth {
+  ip_addr sender;
+  u32 pc;
+  u8 pc_seen;
+  u8 index_len;
+  u8 *index;
+  u8 challenge_reply_seen;
+  u8 challenge_reply[BABEL_AUTH_NONCE_LEN];
+  u8 challenge_seen;
+  u8 challenge_len;
+  u8 challenge[BABEL_AUTH_MAX_NONCE_LEN];
+};
+
 static inline int babel_sadr_enabled(struct babel_proto *p)
 { return p->ip6_rtable.addr_type == NET_IP6_SADR; }
 
@@ -374,11 +422,15 @@ void babel_show_neighbors(struct proto *P, const char *iff);
 void babel_show_entries(struct proto *P);
 void babel_show_routes(struct proto *P);
 
+void babel_auth_reset_index(struct babel_iface *ifa);
+int babel_auth_check_pc(struct babel_iface *ifa, struct babel_msg_auth *msg);
+
 /* packets.c */
 void babel_enqueue(union babel_msg *msg, struct babel_iface *ifa);
 void babel_send_unicast(union babel_msg *msg, struct babel_iface *ifa, ip_addr dest);
 int babel_open_socket(struct babel_iface *ifa);
 void babel_send_queue(void *arg);
+void babel_auth_set_tx_overhead(struct babel_iface *ifa);
 
 
 #endif