BFD: Authentication

Implement BFD authentication (part of RFC 5880). Supports plaintext
passwords and cryptographic MD5 / SHA-1 authentication.

Based on former commit from Pavel Tvrdik

1 files changed, 232 insertions, 13 deletions

diff --git a/proto/bfd/packets.c b/proto/bfd/packets.c
index deb501fc..129db72f 100644
--- a/proto/bfd/packets.c
+++ b/proto/bfd/packets.c
@@ -5,24 +5,60 @@
  */
 
 #include "bfd.h"
+#include "lib/mac.h"
 
 
 struct bfd_ctl_packet
 {
-  u8 vdiag;			/* version and diagnostic */
-  u8 flags;			/* state and flags */
+  u8 vdiag;				/* Version and diagnostic */
+  u8 flags;				/* State and flags */
   u8 detect_mult;
-  u8 length;
-  u32 snd_id;			/* sender ID, aka 'my discriminator' */
-  u32 rcv_id;			/* receiver ID, aka 'your discriminator' */
+  u8 length;				/* Whole packet length */
+  u32 snd_id;				/* Sender ID, aka 'my discriminator' */
+  u32 rcv_id;				/* Receiver ID, aka 'your discriminator' */
   u32 des_min_tx_int;
   u32 req_min_rx_int;
   u32 req_min_echo_rx_int;
 };
 
+struct bfd_auth
+{
+  u8 type;				/* Authentication type (BFD_AUTH_*) */
+  u8 length;				/* Authentication section length */
+};
+
+struct bfd_simple_auth
+{
+  u8 type;				/* BFD_AUTH_SIMPLE */
+  u8 length;				/* Length of bfd_simple_auth + pasword length */
+  u8 key_id;				/* Key ID */
+  byte password[0];			/* Password itself, variable length */
+};
+
+#define BFD_MAX_PASSWORD_LENGTH 16
+
+struct bfd_crypto_auth
+{
+  u8 type;				/* BFD_AUTH_*_MD5 or BFD_AUTH_*_SHA1 */
+  u8 length;				/* Length of bfd_crypto_auth + hash length */
+  u8 key_id;				/* Key ID */
+  u8 zero;				/* Reserved, zero on transmit */
+  u32 csn;				/* Cryptographic sequence number */
+  byte data[0];				/* Authentication key/hash, length 16 or 20 */
+};
+
 #define BFD_BASE_LEN	sizeof(struct bfd_ctl_packet)
 #define BFD_MAX_LEN	64
 
+#define DROP(DSC,VAL) do { err_dsc = DSC; err_val = VAL; goto drop; } while(0)
+
+#define LOG_PKT(msg, args...) \
+  log(L_REMOTE "%s: " msg, p->p.name, args)
+
+#define LOG_PKT_AUTH(msg, args...) \
+  log(L_AUTH "%s: " msg, p->p.name, args)
+
+
 static inline u8 bfd_pack_vdiag(u8 version, u8 diag)
 { return (version << 5) | diag; }
 
@@ -59,6 +95,189 @@ bfd_format_flags(u8 flags, char *buf)
   return buf;
 }
 
+const u8 bfd_auth_type_to_hash_alg[] = {
+    [BFD_AUTH_NONE] = 			ALG_UNDEFINED,
+    [BFD_AUTH_SIMPLE] = 		ALG_UNDEFINED,
+    [BFD_AUTH_KEYED_MD5] = 		ALG_MD5,
+    [BFD_AUTH_METICULOUS_KEYED_MD5] = 	ALG_MD5,
+    [BFD_AUTH_KEYED_SHA1] = 		ALG_SHA1,
+    [BFD_AUTH_METICULOUS_KEYED_SHA1] = 	ALG_SHA1,
+};
+
+
+/* Fill authentication section and modifies final length in control section packet */
+static void
+bfd_fill_authentication(struct bfd_proto *p, struct bfd_session *s, struct bfd_ctl_packet *pkt)
+{
+  struct bfd_iface_config *cf = s->ifa->cf;
+  struct password_item *pass = password_find(cf->passwords, 0);
+  uint meticulous = 0;
+
+  if (!pass)
+  {
+    /* FIXME: This should not happen */
+    log(L_ERR "%s: No suitable password found for authentication", p->p.name);
+    return;
+  }
+
+  switch (cf->auth_type)
+  {
+  case BFD_AUTH_SIMPLE:
+  {
+    struct bfd_simple_auth *auth = (void *) (pkt + 1);
+    uint pass_len = MIN(pass->length, BFD_MAX_PASSWORD_LENGTH);
+
+    auth->type = BFD_AUTH_SIMPLE;
+    auth->length = sizeof(struct bfd_simple_auth) + pass_len;
+    auth->key_id = pass->id;
+
+    pkt->flags |= BFD_FLAG_AP;
+    pkt->length += auth->length;
+
+    memcpy(auth->password, pass->password, pass_len);
+    return;
+  }
+
+  case BFD_AUTH_METICULOUS_KEYED_MD5:
+  case BFD_AUTH_METICULOUS_KEYED_SHA1:
+    meticulous = 1;
+
+  case BFD_AUTH_KEYED_MD5:
+  case BFD_AUTH_KEYED_SHA1:
+  {
+    struct bfd_crypto_auth *auth = (void *) (pkt + 1);
+    uint hash_alg = bfd_auth_type_to_hash_alg[cf->auth_type];
+    uint hash_len = mac_type_length(pass->alg);
+
+    /* Increase CSN about one time per second */
+    u32  new_time = (u64) current_time() >> 20;
+    if ((new_time != s->tx_csn_time) || meticulous)
+    {
+      s->tx_csn++;
+      s->tx_csn_time = new_time;
+    }
+
+    DBG("[%I] CSN: %u\n", s->addr, s->last_tx_csn);
+
+    auth->type = cf->auth_type;
+    auth->length = sizeof(struct bfd_crypto_auth) + hash_len;
+    auth->key_id = pass->id;
+    auth->zero = 0;
+    auth->csn = htonl(s->tx_csn);
+
+    pkt->flags |= BFD_FLAG_AP;
+    pkt->length += auth->length;
+
+    strncpy(auth->data, pass->password, hash_len);
+    mac_fill(hash_alg, NULL, 0, (byte *) pkt, pkt->length, auth->data);
+    return;
+  }
+  }
+}
+
+static int
+bfd_check_authentication(struct bfd_proto *p, struct bfd_session *s, struct bfd_ctl_packet *pkt)
+{
+  struct bfd_iface_config *cf = s->ifa->cf;
+  const char *err_dsc = NULL;
+  uint err_val = 0;
+  uint auth_type = 0;
+  uint meticulous = 0;
+
+  if (pkt->flags & BFD_FLAG_AP)
+  {
+    struct bfd_auth *auth = (void *) (pkt + 1);
+
+    if ((pkt->length < (BFD_BASE_LEN + sizeof(struct bfd_auth))) ||
+	(pkt->length < (BFD_BASE_LEN + auth->length)))
+      DROP("packet length mismatch", pkt->length);
+
+    /* Zero is reserved, we use it as BFD_AUTH_NONE internally */
+    if (auth->type == 0)
+      DROP("reserved authentication type", 0);
+
+    auth_type = auth->type;
+  }
+
+  if (auth_type != cf->auth_type)
+    DROP("authentication method mismatch", auth_type);
+
+  switch (auth_type)
+  {
+  case BFD_AUTH_NONE:
+    return 1;
+
+  case BFD_AUTH_SIMPLE:
+  {
+    struct bfd_simple_auth *auth = (void *) (pkt + 1);
+
+    if (auth->length < sizeof(struct bfd_simple_auth))
+      DROP("wrong authentication length", auth->length);
+
+    struct password_item *pass = password_find_by_id(cf->passwords, auth->key_id);
+    if (!pass)
+      DROP("no suitable password found", auth->key_id);
+
+    uint pass_len = MIN(pass->length, BFD_MAX_PASSWORD_LENGTH);
+    uint auth_len = sizeof(struct bfd_simple_auth) + pass_len;
+
+    if ((auth->length != auth_len) || memcmp(auth->password, pass->password, pass_len))
+      DROP("wrong password", pass->id);
+
+    return 1;
+  }
+
+  case BFD_AUTH_METICULOUS_KEYED_MD5:
+  case BFD_AUTH_METICULOUS_KEYED_SHA1:
+    meticulous = 1;
+
+  case BFD_AUTH_KEYED_MD5:
+  case BFD_AUTH_KEYED_SHA1:
+  {
+    struct bfd_crypto_auth *auth = (void *) (pkt + 1);
+    uint hash_alg = bfd_auth_type_to_hash_alg[cf->auth_type];
+    uint hash_len = mac_type_length(hash_alg);
+
+    if (auth->length != (sizeof(struct bfd_crypto_auth) + hash_len))
+      DROP("wrong authentication length", auth->length);
+
+    struct password_item *pass = password_find_by_id(cf->passwords, auth->key_id);
+    if (!pass)
+      DROP("no suitable password found", auth->key_id);
+
+    /* BFD CSNs are in 32-bit circular number space */
+    u32 csn = ntohl(auth->csn);
+    if (s->rx_csn_known &&
+	(((csn - s->rx_csn) > (3 * s->detect_mult)) ||
+	 (meticulous && (csn == s->rx_csn))))
+    {
+      /* We want to report both new and old CSN */
+      LOG_PKT_AUTH("Authentication failed for %I - "
+		   "wrong sequence number (rcv %u, old %u)",
+		   s->addr, csn, s->rx_csn);
+      return 0;
+    }
+
+    byte *auth_data = alloca(hash_len);
+    memcpy(auth_data, auth->data, hash_len);
+    strncpy(auth->data, pass->password, hash_len);
+
+    if (!mac_verify(hash_alg, NULL, 0, (byte *) pkt, pkt->length, auth_data))
+      DROP("wrong authentication code", pass->id);
+
+    s->rx_csn = csn;
+    s->rx_csn_known = 1;
+
+    return 1;
+  }
+  }
+
+drop:
+  LOG_PKT_AUTH("Authentication failed for %I - %s (%u)",
+	       s->addr, err_dsc, err_val);
+  return 0;
+}
+
 void
 bfd_send_ctl(struct bfd_proto *p, struct bfd_session *s, int final)
 {
@@ -85,6 +304,9 @@ bfd_send_ctl(struct bfd_proto *p, struct bfd_session *s, int final)
   else if (s->poll_active)
     pkt->flags |= BFD_FLAG_POLL;
 
+  if (s->ifa->cf->auth_type)
+    bfd_fill_authentication(p, s, pkt);
+
   if (sk->tbuf != sk->tpos)
     log(L_WARN "%s: Old packet overwritten in TX buffer", p->p.name);
 
@@ -94,8 +316,6 @@ bfd_send_ctl(struct bfd_proto *p, struct bfd_session *s, int final)
   sk_send_to(sk, pkt->length, s->addr, sk->dport);
 }
 
-#define DROP(DSC,VAL) do { err_dsc = DSC; err_val = VAL; goto drop; } while(0)
-
 static int
 bfd_rx_hook(sock *sk, uint len)
 {
@@ -151,10 +371,9 @@ bfd_rx_hook(sock *sk, uint len)
       return 1;
   }
 
-  /* FIXME: better authentication handling and message */
-  if (pkt->flags & BFD_FLAG_AP)
-    DROP("authentication not supported", 0);
-
+  /* bfd_check_authentication() has its own error logging */
+  if (!bfd_check_authentication(p, s, pkt))
+    return 1;
 
   u32 old_tx_int = s->des_min_tx_int;
   u32 old_rx_int = s->rem_min_rx_int;
@@ -173,8 +392,8 @@ bfd_rx_hook(sock *sk, uint len)
   bfd_session_process_ctl(s, pkt->flags, old_tx_int, old_rx_int);
   return 1;
 
- drop:
-  log(L_REMOTE "%s: Bad packet from %I - %s (%u)", p->p.name, sk->faddr, err_dsc, err_val);
+drop:
+  LOG_PKT("Bad packet from %I - %s (%u)", sk->faddr, err_dsc, err_val);
   return 1;
 }