/*
 *	BIRD -- The Babel protocol
 *
 *	Copyright (c) 2015--2016 Toke Hoiland-Jorgensen
 * 	(c) 2016--2017 Ondrej Zajicek <santiago@crfreenet.org>
 *	(c) 2016--2017 CZ.NIC z.s.p.o.
 *
 *	Can be freely distributed and used under the terms of the GNU GPL.
 *
 *	This file contains the packet and TLV handling code for the protocol.
 */

#include "babel.h"
#include "lib/mac.h"


struct babel_pkt_header {
  u8 magic;
  u8 version;
  u16 length;
} PACKED;

struct babel_tlv {
  u8 type;
  u8 length;
  u8 value[0];
} PACKED;

struct babel_tlv_ack_req {
  u8 type;
  u8 length;
  u16 reserved;
  u16 nonce;
  u16 interval;
} PACKED;

struct babel_tlv_ack {
  u8 type;
  u8 length;
  u16 nonce;
} PACKED;

struct babel_tlv_hello {
  u8 type;
  u8 length;
  u16 flags;
  u16 seqno;
  u16 interval;
} PACKED;

struct babel_tlv_ihu {
  u8 type;
  u8 length;
  u8 ae;
  u8 reserved;
  u16 rxcost;
  u16 interval;
  u8 addr[0];
} PACKED;

struct babel_subtlv_timestamp {
  u8 type;
  u8 length;
  u32 tstamp;
  u32 tstamp_rcvd; /* only used in IHU */
} PACKED;

struct babel_tlv_router_id {
  u8 type;
  u8 length;
  u16 reserved;
  u64 router_id;
} PACKED;

struct babel_tlv_next_hop {
  u8 type;
  u8 length;
  u8 ae;
  u8 reserved;
  u8 addr[0];
} PACKED;

struct babel_tlv_update {
  u8 type;
  u8 length;
  u8 ae;
  u8 flags;
  u8 plen;
  u8 omitted;
  u16 interval;
  u16 seqno;
  u16 metric;
  u8 addr[0];
} PACKED;

struct babel_tlv_route_request {
  u8 type;
  u8 length;
  u8 ae;
  u8 plen;
  u8 addr[0];
} PACKED;

struct babel_tlv_seqno_request {
  u8 type;
  u8 length;
  u8 ae;
  u8 plen;
  u16 seqno;
  u8 hop_count;
  u8 reserved;
  u64 router_id;
  u8 addr[0];
} PACKED;

struct babel_subtlv_source_prefix {
  u8 type;
  u8 length;
  u8 plen;
  u8 addr[0];
} PACKED;

struct babel_tlv_mac {
  u8 type;
  u8 length;
  u8 mac[0];
} PACKED;

struct babel_tlv_pc {
  u8 type;
  u8 length;
  u32 pc;
  u8 index[0];
} PACKED;

struct babel_tlv_challenge {
  u8 type;
  u8 length;
  u8 nonce[0];
} PACKED;

struct babel_mac_pseudoheader {
  u8 src_addr[16];
  u16 src_port;
  u8 dst_addr[16];
  u16 dst_port;
} PACKED;

/* Hello flags */
#define BABEL_HF_UNICAST	0x8000

/* Update flags */
#define BABEL_UF_DEF_PREFIX	0x80
#define BABEL_UF_ROUTER_ID	0x40

struct babel_parse_state;
struct babel_write_state;

struct babel_tlv_data {
  u8 min_length;
  int (*read_tlv)(struct babel_tlv *hdr, union babel_msg *m, struct babel_parse_state *state);
  uint (*write_tlv)(struct babel_tlv *hdr, union babel_msg *m, struct babel_write_state *state, uint max_len);
  void (*handle_tlv)(union babel_msg *m, struct babel_iface *ifa);
};

struct babel_parse_state {
  const struct babel_tlv_data* (*get_tlv_data)(u8 type);
  const struct babel_tlv_data* (*get_subtlv_data)(u8 type);
  struct babel_proto *proto;
  struct babel_iface *ifa;
  btime received_time;
  ip_addr saddr;
  ip_addr next_hop_ip4;
  ip_addr next_hop_ip6;
  u64 router_id;		/* Router ID used in subsequent updates */
  u8 def_ip6_prefix[16];	/* Implicit IPv6 prefix in network order */
  u8 def_ip4_prefix[4];		/* Implicit IPv4 prefix (AE 1) in network order */
  u8 def_ip4_via_ip6_prefix[4];	/* Implicit IPv4 prefix (AE 4) in network order */
  u8 router_id_seen;		/* router_id field is valid */
  u8 def_ip6_prefix_seen;	/* def_ip6_prefix is valid */
  u8 def_ip4_prefix_seen;	/* def_ip4_prefix is valid */
  u8 def_ip4_via_ip6_prefix_seen; /* def_ip4_via_ip6_prefix is valid */
  u8 hello_tstamp_seen;	/* pkt contains a hello timestamp */
  u8 current_tlv_endpos;	/* End of self-terminating TLVs (offset from start) */
  u8 sadr_enabled;
  u8 is_unicast;

  struct babel_msg_auth auth;
};

enum parse_result {
  PARSE_SUCCESS,
  PARSE_ERROR,
  PARSE_IGNORE,
};

struct babel_write_state {
  u64 router_id;
  u8 router_id_seen;
  ip_addr next_hop_ip4;
  ip_addr next_hop_ip6;
  u8 def_ip6_prefix[16];	/* Implicit IPv6 prefix in network order */
  u8 def_ip6_pxlen;
};


#define DROP(DSC,VAL) do { err_dsc = DSC; err_val = VAL; goto drop; } while(0)
#define DROP1(DSC) do { err_dsc = DSC; goto drop; } while(0)
#define LOG_PKT(msg, args...) \
  log_rl(&p->log_pkt_tbf, L_REMOTE "%s: " msg, p->p.name, args)
#define LOG_WARN(msg, args...) \
  log_rl(&p->log_pkt_tbf, L_WARN "%s: " msg, p->p.name, args)
#define LOG_PKT_AUTH(msg, args...) \
  log_rl(&p->log_pkt_tbf, L_AUTH "%s: " msg, p->p.name, args)

#define FIRST_TLV(p) ((struct babel_tlv *) (((struct babel_pkt_header *) p) + 1))
#define NEXT_TLV(t) ((struct babel_tlv *) (((byte *) t) + TLV_LENGTH(t)))
#define TLV_LENGTH(t) (t->type == BABEL_TLV_PAD1 ? 1 : t->length + sizeof(struct babel_tlv))
#define TLV_OPT_LENGTH(t) (t->length + sizeof(struct babel_tlv) - sizeof(*t))
#define TLV_HDR(tlv,t,l) ({ tlv->type = t; tlv->length = l - sizeof(struct babel_tlv); })
#define TLV_HDR0(tlv,t) TLV_HDR(tlv, t, tlv_data[t].min_length)

#define NET_SIZE(n) BYTES(net_pxlen(n))


/* Helper macros to loop over a series of TLVs.
 * @start      pointer to first TLV (void * or struct babel_tlv *)
 * @end        byte * pointer to TLV stream end
 * @tlv        struct babel_tlv pointer used as iterator
 * @frame_err  boolean (u8) that will be set to 1 if a frame error occurred
 * @saddr      source addr for use in log output
 * @ifname     ifname for use in log output
 */
#define WALK_TLVS(start, end, tlv, frame_err, saddr, ifname)    \
  for (tlv = start;						\
       (byte *)tlv < end;                                               \
       tlv = NEXT_TLV(tlv))						\
  {									\
    byte *loop_pos;							\
    /* Ugly special case */						\
    if (tlv->type == BABEL_TLV_PAD1)					\
      continue;                                                         \
									\
    /* The end of the common TLV header */				\
    loop_pos = (byte *)tlv + sizeof(struct babel_tlv);			\
    if ((loop_pos > end) || (loop_pos + tlv->length > end))             \
    {                                                                   \
      LOG_PKT("Bad TLV from %I via %s type %d pos %d - framing error",  \
	      saddr, ifname, tlv->type, (int) ((byte *)tlv - (byte *)start)); \
      frame_err = 1;                                                    \
      break;                                                            \
    }

#define WALK_TLVS_END }

static inline uint
bytes_equal(u8 *b1, u8 *b2, uint maxlen)
{
  uint i;
  for (i = 0; (i < maxlen) && (*b1 == *b2); i++, b1++, b2++)
    ;
  return i;
}

static inline uint
get_time16(const void *p)
{
  uint v = get_u16(p) * BABEL_TIME_UNITS;
  return MAX(BABEL_MIN_INTERVAL, v);
}

static inline void
put_time16(void *p, uint v)
{
  put_u16(p, v / BABEL_TIME_UNITS);
}

static inline void
read_ip4_px(net_addr *n, const void *p, uint plen)
{
  ip4_addr addr = {0};
  memcpy(&addr, p, BYTES(plen));
  net_fill_ip4(n, ip4_ntoh(addr), plen);
}

static inline void
put_ip4_px(void *p, net_addr *n)
{
  ip4_addr addr = ip4_hton(net4_prefix(n));
  memcpy(p, &addr, NET_SIZE(n));
}

static inline void
read_ip6_px(net_addr *n, const void *p, uint plen)
{
  ip6_addr addr = IPA_NONE;
  memcpy(&addr, p, BYTES(plen));
  net_fill_ip6(n, ip6_ntoh(addr), plen);
}

static inline void
put_ip6_px(void *p, net_addr *n)
{
  ip6_addr addr = ip6_hton(net6_prefix(n));
  memcpy(p, &addr, NET_SIZE(n));
}

static inline ip6_addr
get_ip6_ll(const void *p)
{
  return ip6_build(0xfe800000, 0, get_u32(p+0), get_u32(p+4));
}

static inline void
put_ip6_ll(void *p, ip6_addr addr)
{
  put_u32(p+0, _I2(addr));
  put_u32(p+4, _I3(addr));
}


/*
 *      Authentication-related functions
 */

uint babel_auth_write_challenge(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, uint max_len);
int babel_auth_add_tlvs(struct babel_iface *ifa, struct babel_tlv *tlv, uint max_len);
int babel_auth_sign(struct babel_iface *ifa, ip_addr dest);
int babel_auth_check(struct babel_iface *ifa,
                     ip_addr saddr, u16 sport,
                     ip_addr daddr, u16 dport,
                     struct babel_pkt_header *pkt,
                     byte *start, uint len);

/*
 *	TLV read/write functions
 */

static int babel_read_ack_req(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
static int babel_read_hello(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
static int babel_read_ihu(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
static int babel_read_router_id(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
static int babel_read_next_hop(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
static int babel_read_update(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
static int babel_read_route_request(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
static int babel_read_seqno_request(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
static int babel_read_source_prefix(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);
static int babel_read_timestamp(struct babel_tlv *hdr, union babel_msg *msg, struct babel_parse_state *state);

static uint babel_write_ack(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, uint max_len);
static uint babel_write_hello(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, uint max_len);
static uint babel_write_ihu(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, uint max_len);
static uint babel_write_update(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, uint max_len);
static uint babel_write_route_request(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, uint max_len);
static uint babel_write_seqno_request(struct babel_tlv *hdr, union babel_msg *msg, struct babel_write_state *state, uint max_len);
static int babel_write_source_prefix(struct babel_tlv *hdr, net_addr *net, uint max_len);
static int babel_write_timestamp(struct babel_tlv *hdr, u32 tstamp, u32 tstamp_rcvd, uint max_len);

static const struct babel_tlv_data tlv_data[BABEL_TLV_MAX] = {
  [BABEL_TLV_ACK_REQ] = {
    sizeof(struct babel_tlv_ack_req),
    babel_read_ack_req,
    NULL,
    babel_handle_ack_req
  },
  [BABEL_TLV_ACK] = {
    sizeof(struct babel_tlv_ack),
    NULL,
    babel_write_ack,
    NULL
  },
  [BABEL_TLV_HELLO] = {
    sizeof(struct babel_tlv_hello),
    babel_read_hello,
    babel_write_hello,
    babel_handle_hello
  },
  [BABEL_TLV_IHU] = {
    sizeof(struct babel_tlv_ihu),
    babel_read_ihu,
    babel_write_ihu,
    babel_handle_ihu
  },
  [BABEL_TLV_ROUTER_ID] = {
    sizeof(struct babel_tlv_router_id),
    babel_read_router_id,
    NULL,
    NULL
  },
  [BABEL_TLV_NEXT_HOP] = {
    sizeof(struct babel_tlv_next_hop),
    babel_read_next_hop,
    NULL,
    NULL
  },
  [BABEL_TLV_UPDATE] = {
    sizeof(struct babel_tlv_update),
    babel_read_update,
    babel_write_update,
    babel_handle_update
  },
  [BABEL_TLV_ROUTE_REQUEST] = {
    sizeof(struct babel_tlv_route_request),
    babel_read_route_request,
    babel_write_route_request,
    babel_handle_route_request
  },
  [BABEL_TLV_SEQNO_REQUEST] = {
    sizeof(struct babel_tlv_seqno_request),
    babel_read_seqno_request,
    babel_write_seqno_request,
    babel_handle_seqno_request
  },
  [BABEL_TLV_CHALLENGE_REQUEST] = {
    sizeof(struct babel_tlv_challenge),
    NULL,
    babel_auth_write_challenge,
    NULL
  },
  [BABEL_TLV_CHALLENGE_REPLY] = {
    sizeof(struct babel_tlv_challenge),
    NULL,
    babel_auth_write_challenge,
    NULL
  },
};

static const struct babel_tlv_data *get_packet_tlv_data(u8 type)
{
  return type < sizeof(tlv_data) / sizeof(*tlv_data) ? &tlv_data[type] : NULL;
}

static const struct babel_tlv_data timestamp_tlv_data = {
  sizeof(struct babel_subtlv_timestamp),
  babel_read_timestamp,
  NULL,
  NULL
};

static const struct babel_tlv_data source_prefix_tlv_data = {
  sizeof(struct babel_subtlv_source_prefix),
  babel_read_source_prefix,
  NULL,
  NULL
};

static const struct babel_tlv_data *get_packet_subtlv_data(u8 type)
{
  switch (type)
  {
  case BABEL_SUBTLV_TIMESTAMP:
    return &timestamp_tlv_data;
  case BABEL_SUBTLV_SOURCE_PREFIX:
    return &source_prefix_tlv_data;

  default:
    return NULL;
  }
}

static int
babel_read_ack_req(struct babel_tlv *hdr, union babel_msg *m,
		   struct babel_parse_state *state)
{
  struct babel_tlv_ack_req *tlv = (void *) hdr;
  struct babel_msg_ack_req *msg = &m->ack_req;

  msg->type = BABEL_TLV_ACK_REQ;
  msg->nonce = get_u16(&tlv->nonce);
  msg->interval = get_time16(&tlv->interval);
  msg->sender = state->saddr;

  if (!msg->interval)
    return PARSE_ERROR;

  return PARSE_SUCCESS;
}

static uint
babel_write_ack(struct babel_tlv *hdr, union babel_msg *m,
                struct babel_write_state *state UNUSED, uint max_len UNUSED)
{
  struct babel_tlv_ack *tlv = (void *) hdr;
  struct babel_msg_ack *msg = &m->ack;

  TLV_HDR0(tlv, BABEL_TLV_ACK);
  put_u16(&tlv->nonce, msg->nonce);

  return sizeof(struct babel_tlv_ack);
}

static int
babel_read_hello(struct babel_tlv *hdr, union babel_msg *m,
                 struct babel_parse_state *state)
{
  struct babel_tlv_hello *tlv = (void *) hdr;
  struct babel_msg_hello *msg = &m->hello;

  /* We currently don't support unicast Hello */
  u16 flags = get_u16(&tlv->flags);
  if (flags & BABEL_HF_UNICAST)
    return PARSE_IGNORE;

  msg->type = BABEL_TLV_HELLO;
  msg->seqno = get_u16(&tlv->seqno);
  msg->interval = get_time16(&tlv->interval);
  msg->sender = state->saddr;

  return PARSE_SUCCESS;
}

static uint
babel_write_hello(struct babel_tlv *hdr, union babel_msg *m,
                  struct babel_write_state *state UNUSED, uint max_len)
{
  struct babel_tlv_hello *tlv = (void *) hdr;
  struct babel_msg_hello *msg = &m->hello;
  uint len = sizeof(struct babel_tlv_hello);

  TLV_HDR0(tlv, BABEL_TLV_HELLO);
  put_u16(&tlv->seqno, msg->seqno);
  put_time16(&tlv->interval, msg->interval);

  if (msg->tstamp)
  {
    /*
     * There can be a substantial delay between when the babel_msg was created
     * and when it is serialised. We don't want this included in the RTT
     * measurement, so replace the timestamp with the current time to get as
     * close as possible to on-wire time for the packet.
     */
    u32 tstamp = current_time_now() TO_US;

    int l = babel_write_timestamp(hdr, tstamp, 0, max_len);
    if (l < 0)
      return 0;

    len += l;
  }

  return len;
}

static int
babel_read_ihu(struct babel_tlv *hdr, union babel_msg *m,
               struct babel_parse_state *state)
{
  struct babel_tlv_ihu *tlv = (void *) hdr;
  struct babel_msg_ihu *msg = &m->ihu;

  msg->type = BABEL_TLV_IHU;
  msg->ae = tlv->ae;
  msg->rxcost = get_u16(&tlv->rxcost);
  msg->interval = get_time16(&tlv->interval);
  msg->addr = IPA_NONE;
  msg->sender = state->saddr;

  /*
   * We only actually read link-local IPs. In every other case, the addr field
   * will be 0 but validation will succeed. The handler takes care of these
   * cases. We handle them here anyway because we need the length for parsing
   * subtlvs.
   */
  switch (msg->ae)
  {
  case BABEL_AE_WILDCARD:
    return PARSE_SUCCESS;

  case BABEL_AE_IP4:
    if (TLV_OPT_LENGTH(tlv) < 4)
      return PARSE_ERROR;
    state->current_tlv_endpos += 4;
    return PARSE_SUCCESS;

  case BABEL_AE_IP6:
    if (TLV_OPT_LENGTH(tlv) < 16)
      return PARSE_ERROR;
    state->current_tlv_endpos += 16;
    return PARSE_SUCCESS;

  case BABEL_AE_IP6_LL:
    if (TLV_OPT_LENGTH(tlv) < 8)
      return PARSE_ERROR;

    msg->addr = ipa_from_ip6(get_ip6_ll(&tlv->addr));
    state->current_tlv_endpos += 8;
    return PARSE_SUCCESS;

  /* RFC 9229 2.4 - IHU TLV MUST NOT carry the AE 4 (IPv4-via-IPv6) */
  case BABEL_AE_IP4_VIA_IP6:
    return PARSE_ERROR;

  default:
    return PARSE_IGNORE;
  }

  return PARSE_IGNORE;
}

static uint
babel_write_ihu(struct babel_tlv *hdr, union babel_msg *m,
                struct babel_write_state *state UNUSED, uint max_len)
{
  struct babel_tlv_ihu *tlv = (void *) hdr;
  struct babel_msg_ihu *msg = &m->ihu;
  uint len = sizeof(*tlv);

  if (ipa_is_link_local(msg->addr) && max_len < sizeof(struct babel_tlv_ihu) + 8)
    return 0;

  TLV_HDR0(tlv, BABEL_TLV_IHU);
  put_u16(&tlv->rxcost, msg->rxcost);
  put_time16(&tlv->interval, msg->interval);

  if (!ipa_is_link_local(msg->addr))
  {
    tlv->ae = BABEL_AE_WILDCARD;
    goto out;
  }
  put_ip6_ll(&tlv->addr, msg->addr);
  tlv->ae = BABEL_AE_IP6_LL;
  hdr->length += 8;
  len += 8;

out:
  if (msg->tstamp)
  {
    int l = babel_write_timestamp(hdr, msg->tstamp, msg->tstamp_rcvd, max_len);
    if (l < 0)
      return 0;

    len += l;
  }

  return len;
}

static int
babel_read_router_id(struct babel_tlv *hdr, union babel_msg *m UNUSED,
                     struct babel_parse_state *state)
{
  struct babel_tlv_router_id *tlv = (void *) hdr;

  state->router_id = get_u64(&tlv->router_id);
  state->router_id_seen = 1;

  return PARSE_IGNORE;
}

/* This is called directly from babel_write_update() */
static uint
babel_write_router_id(struct babel_tlv *hdr, u64 router_id,
		      struct babel_write_state *state, uint max_len UNUSED)
{
  struct babel_tlv_router_id *tlv = (void *) hdr;

  /* We still assume that first min_length bytes are available and zeroed */

  TLV_HDR0(tlv, BABEL_TLV_ROUTER_ID);
  put_u64(&tlv->router_id, router_id);

  state->router_id = router_id;
  state->router_id_seen = 1;

  return sizeof(struct babel_tlv_router_id);
}

static int
babel_read_next_hop(struct babel_tlv *hdr, union babel_msg *m UNUSED,
                    struct babel_parse_state *state)
{
  struct babel_tlv_next_hop *tlv = (void *) hdr;

  switch (tlv->ae)
  {
  case BABEL_AE_WILDCARD:
    return PARSE_ERROR;

  case BABEL_AE_IP4:
    if (TLV_OPT_LENGTH(tlv) < sizeof(ip4_addr))
      return PARSE_ERROR;

    state->next_hop_ip4 = ipa_from_ip4(get_ip4(&tlv->addr));
    state->current_tlv_endpos += sizeof(ip4_addr);
    return PARSE_IGNORE;

  case BABEL_AE_IP6:
    if (TLV_OPT_LENGTH(tlv) < sizeof(ip6_addr))
      return PARSE_ERROR;

    state->next_hop_ip6 = ipa_from_ip6(get_ip6(&tlv->addr));
    state->current_tlv_endpos += sizeof(ip6_addr);
    return PARSE_IGNORE;

  case BABEL_AE_IP6_LL:
    if (TLV_OPT_LENGTH(tlv) < 8)
      return PARSE_ERROR;

    state->next_hop_ip6 = ipa_from_ip6(get_ip6_ll(&tlv->addr));
    state->current_tlv_endpos += 8;
    return PARSE_IGNORE;

  /* RFC 9229 2.4 - Next Hop TLV MUST NOT carry the AE 4 (IPv4-via-IPv6) */
  case BABEL_AE_IP4_VIA_IP6:
    return PARSE_ERROR;

  default:
    return PARSE_IGNORE;
  }

  return PARSE_IGNORE;
}

/* This is called directly from babel_write_update() and returns -1 if a next
   hop should be written but there is not enough space. */
static int
babel_write_next_hop(struct babel_tlv *hdr, ip_addr addr,
		     struct babel_write_state *state, uint max_len)
{
  struct babel_tlv_next_hop *tlv = (void *) hdr;

  if (ipa_zero(addr))
  {
    /* Should not happen */
    return 0;
  }
  else if (ipa_is_ip4(addr) && !ipa_equal(addr, state->next_hop_ip4))
  {
    uint len = sizeof(struct babel_tlv_next_hop) + sizeof(ip4_addr);
    if (len > max_len)
      return -1;

    TLV_HDR(tlv, BABEL_TLV_NEXT_HOP, len);

    tlv->ae = BABEL_AE_IP4;
    put_ip4(&tlv->addr, ipa_to_ip4(addr));
    state->next_hop_ip4 = addr;

    return len;
  }
  else if (ipa_is_ip6(addr) && !ipa_equal(addr, state->next_hop_ip6))
  {
    uint len = sizeof(struct babel_tlv_next_hop) + sizeof(ip6_addr);
    if (len > max_len)
      return -1;

    TLV_HDR(tlv, BABEL_TLV_NEXT_HOP, len);

    tlv->ae = BABEL_AE_IP6;
    put_ip6(&tlv->addr, ipa_to_ip6(addr));
    state->next_hop_ip6 = addr;

    return len;
  }

  return 0;
}

/* This is called directly from babel_read_update() to handle
   both BABEL_AE_IP4 and BABEL_AE_IP4_VIA_IP6 encodings */
static int
babel_read_ip4_prefix(struct babel_tlv_update *tlv, struct babel_msg_update *msg,
		     u8 *def_prefix, u8 *def_prefix_seen, ip_addr next_hop, int len)
{
    if (tlv->plen > IP4_MAX_PREFIX_LENGTH)
      return PARSE_ERROR;

    /* Cannot omit data if there is no saved prefix */
    if (tlv->omitted && !*def_prefix_seen)
      return PARSE_ERROR;

    /* Update must have next hop, unless it is retraction */
    if (ipa_zero(next_hop) && msg->metric != BABEL_INFINITY)
      return PARSE_ERROR;

    /* Merge saved prefix and received prefix parts */
    u8 buf[4] = {};
    memcpy(buf, def_prefix, tlv->omitted);
    memcpy(buf + tlv->omitted, tlv->addr, len);

    ip4_addr prefix4 = get_ip4(buf);
    net_fill_ip4(&msg->net, prefix4, tlv->plen);

    if (tlv->flags & BABEL_UF_DEF_PREFIX)
    {
      put_ip4(def_prefix, prefix4);
      *def_prefix_seen = 1;
    }

    msg->next_hop = next_hop;

    return PARSE_SUCCESS;
}

static int
babel_read_update(struct babel_tlv *hdr, union babel_msg *m,
                  struct babel_parse_state *state)
{
  struct babel_tlv_update *tlv = (void *) hdr;
  struct babel_msg_update *msg = &m->update;

  msg->type = BABEL_TLV_UPDATE;
  msg->interval = get_time16(&tlv->interval);
  msg->seqno = get_u16(&tlv->seqno);
  msg->metric = get_u16(&tlv->metric);

  /* Length of received prefix data without omitted part */
  int len = BYTES(tlv->plen) - (int) tlv->omitted;

  if ((len < 0) || ((uint) len > TLV_OPT_LENGTH(tlv)))
    return PARSE_ERROR;

  int rc;
  switch (tlv->ae)
  {
  case BABEL_AE_WILDCARD:
    if (tlv->plen > 0)
      return PARSE_ERROR;

    if (msg->metric != 65535)
      return PARSE_ERROR;

    msg->wildcard = 1;
    break;

  case BABEL_AE_IP4:
    rc = babel_read_ip4_prefix(tlv, msg, state->def_ip4_prefix,
			       &state->def_ip4_prefix_seen,
			       state->next_hop_ip4, len);
    if (rc != PARSE_SUCCESS)
      return rc;

    break;

  case BABEL_AE_IP4_VIA_IP6:
    rc = babel_read_ip4_prefix(tlv, msg, state->def_ip4_via_ip6_prefix,
			       &state->def_ip4_via_ip6_prefix_seen,
			       state->next_hop_ip6, len);
    if (rc != PARSE_SUCCESS)
      return rc;

    break;

  case BABEL_AE_IP6:
    if (tlv->plen > IP6_MAX_PREFIX_LENGTH)
      return PARSE_ERROR;

    /* Cannot omit data if there is no saved prefix */
    if (tlv->omitted && !state->def_ip6_prefix_seen)
      return PARSE_ERROR;

    /* Merge saved prefix and received prefix parts */
    u8 buf[16] = {};
    memcpy(buf, state->def_ip6_prefix, tlv->omitted);
    memcpy(buf + tlv->omitted, tlv->addr, len);

    ip6_addr prefix6 = get_ip6(buf);
    net_fill_ip6(&msg->net, prefix6, tlv->plen);

    if (state->sadr_enabled)
      net_make_ip6_sadr(&msg->net);

    if (tlv->flags & BABEL_UF_DEF_PREFIX)
    {
      put_ip6(state->def_ip6_prefix, prefix6);
      state->def_ip6_prefix_seen = 1;
    }

    if (tlv->flags & BABEL_UF_ROUTER_ID)
    {
      state->router_id = ((u64) _I2(prefix6)) << 32 | _I3(prefix6);
      state->router_id_seen = 1;
    }

    msg->next_hop = state->next_hop_ip6;

    break;

  case BABEL_AE_IP6_LL:
    /* ??? */
    return PARSE_IGNORE;

  default:
    return PARSE_IGNORE;
  }

  /* Update must have Router ID, unless it is retraction */
  if (!state->router_id_seen && (msg->metric != BABEL_INFINITY))
  {
    DBG("Babel: No router ID seen before update\n");
    return PARSE_ERROR;
  }

  msg->router_id = state->router_id;
  msg->sender = state->saddr;
  state->current_tlv_endpos += len;

  return PARSE_SUCCESS;
}

static uint
babel_write_update(struct babel_tlv *hdr, union babel_msg *m,
                   struct babel_write_state *state, uint max_len)
{
  struct babel_msg_update *msg = &m->update;
  uint len0 = 0;

  /*
   * When needed, we write Router-ID TLV before Update TLV and return size of
   * both of them. There is enough space for the Router-ID TLV, because
   * sizeof(struct babel_tlv_router_id) == sizeof(struct babel_tlv_update).
   *
   * Router ID is not used for retractions, so do not use it in such case.
   */
  if ((msg->metric < BABEL_INFINITY) &&
      (!state->router_id_seen || (msg->router_id != state->router_id)))
  {
    len0 = babel_write_router_id(hdr, msg->router_id, state, max_len);
    hdr = NEXT_TLV(hdr);
  }

  /*
   * We also may add Next Hop TLV for regular updates. It may fail for not
   * enough space or it may be unnecessary as the next hop is the same as the
   * last one already announced. So we handle all three cases.
   */
  if (msg->metric < BABEL_INFINITY)
  {
    int l = babel_write_next_hop(hdr, msg->next_hop, state, max_len - len0);
    if (l < 0)
      return 0;

    if (l)
    {
      len0 += l;
      hdr = NEXT_TLV(hdr);
    }
  }

  struct babel_tlv_update *tlv = (void *) hdr;
  uint len = sizeof(struct babel_tlv_update) + NET_SIZE(&msg->net);

  if (len0 + len > max_len)
    return 0;

  memset(tlv, 0, sizeof(struct babel_tlv_update));
  TLV_HDR(tlv, BABEL_TLV_UPDATE, len);

  if (msg->wildcard)
  {
    tlv->ae = BABEL_AE_WILDCARD;
    tlv->plen = 0;
  }
  else if (msg->net.type == NET_IP4)
  {
    tlv->ae = ipa_is_ip4(msg->next_hop) ? BABEL_AE_IP4 : BABEL_AE_IP4_VIA_IP6;
    tlv->plen = net4_pxlen(&msg->net);
    put_ip4_px(tlv->addr, &msg->net);
  }
  else
  {
    tlv->ae = BABEL_AE_IP6;
    tlv->plen = net6_pxlen(&msg->net);

    /* Address compression - omit initial matching bytes */
    u8 buf[16], omit;
    put_ip6(buf, net6_prefix(&msg->net));
    omit = bytes_equal(buf, state->def_ip6_prefix,
		       MIN(tlv->plen, state->def_ip6_pxlen) / 8);

    if (omit > 0)
    {
      memcpy(tlv->addr, buf + omit, NET_SIZE(&msg->net) - omit);

      tlv->omitted = omit;
      tlv->length -= omit;
      len -= omit;
    }
    else
    {
      put_ip6_px(tlv->addr, &msg->net);
      tlv->flags |= BABEL_UF_DEF_PREFIX;

      put_ip6(state->def_ip6_prefix, net6_prefix(&msg->net));
      state->def_ip6_pxlen = tlv->plen;
    }
  }

  put_time16(&tlv->interval, msg->interval);
  put_u16(&tlv->seqno, msg->seqno);
  put_u16(&tlv->metric, msg->metric);

  if (msg->net.type == NET_IP6_SADR)
  {
    int l = babel_write_source_prefix(hdr, &msg->net, max_len - (len0 + len));
    if (l < 0)
      return 0;

    len += l;
  }

  return len0 + len;
}

static int
babel_read_route_request(struct babel_tlv *hdr, union babel_msg *m,
                         struct babel_parse_state *state)
{
  struct babel_tlv_route_request *tlv = (void *) hdr;
  struct babel_msg_route_request *msg = &m->route_request;

  msg->type = BABEL_TLV_ROUTE_REQUEST;

  switch (tlv->ae)
  {
  case BABEL_AE_WILDCARD:
    /* Wildcard requests must have plen 0 */
    if (tlv->plen > 0)
      return PARSE_ERROR;

    msg->full = 1;
    return PARSE_SUCCESS;

  /*
   * RFC 9229 2.3 - When receiving requests, AE 1 (IPv4) and AE 4
   * (IPv4-via-IPv6) MUST be treated in the same manner.
   */
  case BABEL_AE_IP4:
  case BABEL_AE_IP4_VIA_IP6:
    if (tlv->plen > IP4_MAX_PREFIX_LENGTH)
      return PARSE_ERROR;

    if (TLV_OPT_LENGTH(tlv) < BYTES(tlv->plen))
      return PARSE_ERROR;

    read_ip4_px(&msg->net, tlv->addr, tlv->plen);
    state->current_tlv_endpos += BYTES(tlv->plen);
    return PARSE_SUCCESS;

  case BABEL_AE_IP6:
    if (tlv->plen > IP6_MAX_PREFIX_LENGTH)
      return PARSE_ERROR;

    if (TLV_OPT_LENGTH(tlv) < BYTES(tlv->plen))
      return PARSE_ERROR;

    read_ip6_px(&msg->net, tlv->addr, tlv->plen);
    state->current_tlv_endpos += BYTES(tlv->plen);

    if (state->sadr_enabled)
      net_make_ip6_sadr(&msg->net);

    return PARSE_SUCCESS;

  case BABEL_AE_IP6_LL:
    return PARSE_ERROR;

  default:
    return PARSE_IGNORE;
  }

  return PARSE_IGNORE;
}

static uint
babel_write_route_request(struct babel_tlv *hdr, union babel_msg *m,
			  struct babel_write_state *state UNUSED, uint max_len)
{
  struct babel_tlv_route_request *tlv = (void *) hdr;
  struct babel_msg_route_request *msg = &m->route_request;

  uint len = sizeof(struct babel_tlv_route_request) + NET_SIZE(&msg->net);

  if (len > max_len)
    return 0;

  TLV_HDR(tlv, BABEL_TLV_ROUTE_REQUEST, len);

  if (msg->full)
  {
    tlv->ae = BABEL_AE_WILDCARD;
    tlv->plen = 0;
  }
  else if (msg->net.type == NET_IP4)
  {
    tlv->ae = BABEL_AE_IP4;
    tlv->plen = net4_pxlen(&msg->net);
    put_ip4_px(tlv->addr, &msg->net);
  }
  else
  {
    tlv->ae = BABEL_AE_IP6;
    tlv->plen = net6_pxlen(&msg->net);
    put_ip6_px(tlv->addr, &msg->net);
  }

  if (msg->net.type == NET_IP6_SADR)
  {
    int l = babel_write_source_prefix(hdr, &msg->net, max_len - len);
    if (l < 0)
      return 0;

    len += l;
  }

  return len;
}

static int
babel_read_seqno_request(struct babel_tlv *hdr, union babel_msg *m,
                         struct babel_parse_state *state)
{
  struct babel_tlv_seqno_request *tlv = (void *) hdr;
  struct babel_msg_seqno_request *msg = &m->seqno_request;

  msg->type = BABEL_TLV_SEQNO_REQUEST;
  msg->seqno = get_u16(&tlv->seqno);
  msg->hop_count = tlv->hop_count;
  msg->router_id = get_u64(&tlv->router_id);
  msg->sender = state->saddr;

  if (tlv->hop_count == 0)
    return PARSE_ERROR;

  switch (tlv->ae)
  {
  case BABEL_AE_WILDCARD:
    return PARSE_ERROR;

  /*
   * RFC 9229 2.3 - When receiving requests, AE 1 (IPv4) and AE 4
   * (IPv4-via-IPv6) MUST be treated in the same manner.
   */
  case BABEL_AE_IP4:
  case BABEL_AE_IP4_VIA_IP6:
    if (tlv->plen > IP4_MAX_PREFIX_LENGTH)
      return PARSE_ERROR;

    if (TLV_OPT_LENGTH(tlv) < BYTES(tlv->plen))
      return PARSE_ERROR;

    read_ip4_px(&msg->net, tlv->addr, tlv->plen);
    state->current_tlv_endpos += BYTES(tlv->plen);
    return PARSE_SUCCESS;

  case BABEL_AE_IP6:
    if (tlv->plen > IP6_MAX_PREFIX_LENGTH)
      return PARSE_ERROR;

    if (TLV_OPT_LENGTH(tlv) < BYTES(tlv->plen))
      return PARSE_ERROR;

    read_ip6_px(&msg->net, tlv->addr, tlv->plen);
    state->current_tlv_endpos += BYTES(tlv->plen);

    if (state->sadr_enabled)
      net_make_ip6_sadr(&msg->net);

    return PARSE_SUCCESS;

  case BABEL_AE_IP6_LL:
    return PARSE_ERROR;

  default:
    return PARSE_IGNORE;
  }

  return PARSE_IGNORE;
}

static uint
babel_write_seqno_request(struct babel_tlv *hdr, union babel_msg *m,
			  struct babel_write_state *state UNUSED, uint max_len)
{
  struct babel_tlv_seqno_request *tlv = (void *) hdr;
  struct babel_msg_seqno_request *msg = &m->seqno_request;

  uint len = sizeof(struct babel_tlv_seqno_request) + NET_SIZE(&msg->net);

  if (len > max_len)
    return 0;

  TLV_HDR(tlv, BABEL_TLV_SEQNO_REQUEST, len);

  if (msg->net.type == NET_IP4)
  {
    tlv->ae = BABEL_AE_IP4;
    tlv->plen = net4_pxlen(&msg->net);
    put_ip4_px(tlv->addr, &msg->net);
  }
  else
  {
    tlv->ae = BABEL_AE_IP6;
    tlv->plen = net6_pxlen(&msg->net);
    put_ip6_px(tlv->addr, &msg->net);
  }

  put_u16(&tlv->seqno, msg->seqno);
  tlv->hop_count = msg->hop_count;
  put_u64(&tlv->router_id, msg->router_id);

  if (msg->net.type == NET_IP6_SADR)
  {
    int l = babel_write_source_prefix(hdr, &msg->net, max_len - len);
    if (l < 0)
      return 0;

    len += l;
  }

  return len;
}

static int
babel_read_source_prefix(struct babel_tlv *hdr, union babel_msg *msg,
			 struct babel_parse_state *state UNUSED)
{
  struct babel_subtlv_source_prefix *tlv = (void *) hdr;
  net_addr_ip6_sadr *net;

  /*
   * We would like to skip the sub-TLV if SADR is not enabled, but we do not
   * know AF of the enclosing TLV yet. We will do that later.
   */

  /* Check internal consistency */
  if ((tlv->length < 1) ||
      (tlv->plen > IP6_MAX_PREFIX_LENGTH) ||
      (tlv->length < (1 + BYTES(tlv->plen))))
    return PARSE_ERROR;

  /* Plen MUST NOT be 0 */
  if (tlv->plen == 0)
    return PARSE_ERROR;

  switch (msg->type)
  {
  case BABEL_TLV_UPDATE:
    /* Wildcard updates with source prefix MUST be silently ignored */
    if (msg->update.wildcard)
      return PARSE_IGNORE;

    net = (void *) &msg->update.net;
    break;

  case BABEL_TLV_ROUTE_REQUEST:
    /* Wildcard requests with source addresses MUST be silently ignored */
    if (msg->route_request.full)
      return PARSE_IGNORE;

    net = (void *) &msg->route_request.net;
    break;

  case BABEL_TLV_SEQNO_REQUEST:
    net = (void *) &msg->seqno_request.net;
    break;

  default:
    return PARSE_ERROR;
  }

  /* If SADR is active, the net has appropriate type */
  if (net->type != NET_IP6_SADR)
    return PARSE_IGNORE;

  /* Duplicate Source Prefix sub-TLV; SHOULD ignore whole TLV */
  if (net->src_pxlen > 0)
    return PARSE_IGNORE;

  net_addr_ip6 src;
  read_ip6_px((void *) &src, tlv->addr, tlv->plen);
  net->src_prefix = src.prefix;
  net->src_pxlen = src.pxlen;

  return PARSE_SUCCESS;
}

static int
babel_write_source_prefix(struct babel_tlv *hdr, net_addr *n, uint max_len)
{
  struct babel_subtlv_source_prefix *tlv = (void *) NEXT_TLV(hdr);
  net_addr_ip6_sadr *net = (void *) n;

  /* Do not use this sub-TLV for default prefix */
  if (net->src_pxlen == 0)
    return 0;

  uint len = sizeof(*tlv) + BYTES(net->src_pxlen);

  if (len > max_len)
    return -1;

  TLV_HDR(tlv, BABEL_SUBTLV_SOURCE_PREFIX, len);
  hdr->length += len;

  net_addr_ip6 src = NET_ADDR_IP6(net->src_prefix, net->src_pxlen);
  tlv->plen = src.pxlen;
  put_ip6_px(tlv->addr, (void *) &src);

  return len;
}

static int
babel_read_timestamp(struct babel_tlv *hdr, union babel_msg *msg,
                     struct babel_parse_state *state)
{
  struct babel_subtlv_timestamp *tlv = (void *) hdr;

  switch (msg->type)
  {
  case BABEL_TLV_HELLO:
    if (tlv->length < 4)
      return PARSE_ERROR;

    msg->hello.tstamp = get_u32(&tlv->tstamp);
    msg->hello.pkt_received = state->received_time;
    state->hello_tstamp_seen = 1;
    break;

  case BABEL_TLV_IHU:
    if (tlv->length < 8)
      return PARSE_ERROR;

    /* RTT calculation relies on a Hello always being present with an IHU */
    if (!state->hello_tstamp_seen)
      break;

    msg->ihu.tstamp = get_u32(&tlv->tstamp);
    msg->ihu.tstamp_rcvd = get_u32(&tlv->tstamp_rcvd);
    msg->ihu.pkt_received = state->received_time;
    break;

  default:
    return PARSE_ERROR;
  }

  return PARSE_SUCCESS;
}

static int
babel_write_timestamp(struct babel_tlv *hdr, u32 tstamp, u32 tstamp_rcvd, uint max_len)
{
  struct babel_subtlv_timestamp *tlv = (void *) NEXT_TLV(hdr);
  uint len = sizeof(*tlv);

  if (hdr->type == BABEL_TLV_HELLO)
    len -= 4;

  if (len > max_len)
    return -1;

  TLV_HDR(tlv, BABEL_SUBTLV_TIMESTAMP, len);
  hdr->length += len;

  put_u32(&tlv->tstamp, tstamp);

  if (hdr->type == BABEL_TLV_IHU)
    put_u32(&tlv->tstamp_rcvd, tstamp_rcvd);

  return len;
}

static inline int
babel_read_subtlvs(struct babel_tlv *hdr,
		   union babel_msg *msg,
		   struct babel_parse_state *state)
{
  const struct babel_tlv_data *tlv_data;
  struct babel_proto *p = state->proto;
  struct babel_tlv *tlv;
  byte *end = (byte *) hdr + TLV_LENGTH(hdr);
  u8 frame_err = 0;
  int res;

  WALK_TLVS((void *)hdr + state->current_tlv_endpos, end, tlv, frame_err,
            state->saddr, state->ifa->ifname)
  {
    if (tlv->type == BABEL_SUBTLV_PADN)
      continue;

    if (!state->get_subtlv_data ||
        !(tlv_data = state->get_subtlv_data(tlv->type)) ||
        !tlv_data->read_tlv)
    {
      /* Unknown mandatory subtlv; PARSE_IGNORE ignores the whole TLV */
      if (tlv->type >= 128)
        return PARSE_IGNORE;
      continue;
    }

    res = tlv_data->read_tlv(tlv, msg, state);
    if (res != PARSE_SUCCESS)
      return res;
  }
  WALK_TLVS_END;

  return frame_err ? PARSE_ERROR : PARSE_SUCCESS;
}

static int
babel_read_tlv(struct babel_tlv *hdr,
               union babel_msg *msg,
               struct babel_parse_state *state)
{
  const struct babel_tlv_data *tlv_data;

  if ((hdr->type <= BABEL_TLV_PADN) ||
      (hdr->type >= BABEL_TLV_MAX))
    return PARSE_IGNORE;

  tlv_data = state->get_tlv_data(hdr->type);

  if (!tlv_data || !tlv_data->read_tlv)
    return PARSE_IGNORE;

  if (TLV_LENGTH(hdr) < tlv_data->min_length)
    return PARSE_ERROR;

  state->current_tlv_endpos = tlv_data->min_length;

  int res = tlv_data->read_tlv(hdr, msg, state);
  if (res != PARSE_SUCCESS)
    return res;

  return babel_read_subtlvs(hdr, msg, state);
}

static uint
babel_write_tlv(struct babel_tlv *hdr,
		union babel_msg *msg,
		struct babel_write_state *state,
		uint max_len)
{
  if ((msg->type <= BABEL_TLV_PADN) ||
      (msg->type >= BABEL_TLV_MAX) ||
      !tlv_data[msg->type].write_tlv)
    return 0;

  if (tlv_data[msg->type].min_length > max_len)
    return 0;

  memset(hdr, 0, tlv_data[msg->type].min_length);
  return tlv_data[msg->type].write_tlv(hdr, msg, state, max_len);
}


/*
 *	Packet RX/TX functions
 */

static int
babel_send_to(struct babel_iface *ifa, ip_addr dest)
{
  sock *sk = ifa->sk;
  struct babel_pkt_header *hdr = (void *) sk->tbuf;
  int len = get_u16(&hdr->length) + sizeof(struct babel_pkt_header);

  len += babel_auth_sign(ifa, dest);

  DBG("Babel: Sending %d bytes to %I\n", len, dest);
  return sk_send_to(sk, len, dest, 0);
}

/**
 * babel_write_queue - Write a TLV queue to a transmission buffer
 * @ifa: Interface holding the transmission buffer
 * @queue: TLV queue to write (containing internal-format TLVs)
 *
 * This function writes a packet to the interface transmission buffer with as
 * many TLVs from the &queue as will fit in the buffer. It returns the number of
 * bytes written (NOT counting the packet header). The function is called by
 * babel_send_queue() and babel_send_unicast() to construct packets for
 * transmission, and uses per-TLV helper functions to convert the
 * internal-format TLVs to their wire representations.
 *
 * The TLVs in the queue are freed after they are written to the buffer.
 */
static uint
babel_write_queue(struct babel_iface *ifa, list *queue)
{
  struct babel_write_state state = { .next_hop_ip6 = ifa->addr };

  if (EMPTY_LIST(*queue))
    return 0;

  byte *pos = ifa->sk->tbuf;
  byte *end = pos + ifa->tx_length;

  struct babel_pkt_header *pkt = (void *) pos;
  pkt->magic = BABEL_MAGIC;
  pkt->version = BABEL_VERSION;
  pkt->length = 0;
  pos += sizeof(struct babel_pkt_header);

  struct babel_msg_node *msg;
  WALK_LIST_FIRST(msg, *queue)
  {
    if (pos >= end)
      break;

    int len = babel_write_tlv((struct babel_tlv *) pos, &msg->msg, &state, end - pos);

    if (!len)
      break;

    pos += len;
    rem_node(NODE msg);
    sl_free(msg);
  }

  pos += babel_auth_add_tlvs(ifa, (struct babel_tlv *) pos, end - pos);

  uint plen = pos - (byte *) pkt;
  put_u16(&pkt->length, plen - sizeof(struct babel_pkt_header));

  return plen;
}

void
babel_send_queue(void *arg)
{
  struct babel_iface *ifa = arg;
  ASSERT_DIE(birdloop_inside(ifa->proto->p.loop));
  while ((babel_write_queue(ifa, &ifa->msg_queue) > 0) &&
	 (babel_send_to(ifa, IP6_BABEL_ROUTERS) > 0));
}

static inline void
babel_kick_queue(struct babel_iface *ifa)
{
  /*
   * Only schedule send event if there is not already data in the socket buffer.
   * Otherwise we may overwrite the data already in the buffer.
   */

  if ((ifa->sk->tpos == ifa->sk->tbuf) && !ev_active(ifa->send_event))
    ev_send(proto_event_list(&ifa->proto->p), ifa->send_event);
}

/**
 * babel_send_unicast - send a single TLV via unicast to a destination
 * @msg: TLV to send
 * @ifa: Interface to send via
 * @dest: Destination of the TLV
 *
 * This function is used to send a single TLV via unicast to a designated
 * receiver. This is used for replying to certain incoming requests, and for
 * sending unicast requests to refresh routes before they expire.
 */
void
babel_send_unicast(union babel_msg *msg, struct babel_iface *ifa, ip_addr dest)
{
  struct babel_proto *p = ifa->proto;
  ASSERT_DIE(birdloop_inside(p->p.loop));
  struct babel_msg_node *msgn = sl_alloc(p->msg_slab);
  list queue;

  *msgn = (struct babel_msg_node) { .msg = *msg };
  init_list(&queue);
  add_tail(&queue, NODE msgn);
  babel_write_queue(ifa, &queue);
  babel_send_to(ifa, dest);

  /* We could overwrite waiting packet here, we may have to kick TX queue */
  if (!EMPTY_LIST(ifa->msg_queue))
    babel_kick_queue(ifa);
}

/**
 * babel_enqueue - enqueue a TLV for transmission on an interface
 * @msg: TLV to enqueue (in internal TLV format)
 * @ifa: Interface to enqueue to
 *
 * This function is called to enqueue a TLV for subsequent transmission on an
 * interface. The transmission event is triggered whenever a TLV is enqueued;
 * this ensures that TLVs will be transmitted in a timely manner, but that TLVs
 * which are enqueued in rapid succession can be transmitted together in one
 * packet.
 */
void
babel_enqueue(union babel_msg *msg, struct babel_iface *ifa)
{
  struct babel_proto *p = ifa->proto;
  ASSERT_DIE(birdloop_inside(p->p.loop));
  struct babel_msg_node *msgn = sl_alloc(p->msg_slab);

  *msgn = (struct babel_msg_node) { .msg = *msg };
  add_tail(&ifa->msg_queue, NODE msgn);
  babel_kick_queue(ifa);
}

/**
 * babel_process_packet - process incoming data packet
 * @ifa: Interface packet was received on
 * @pkt: Pointer to the packet data
 * @len: Length of received packet
 * @saddr: Address of packet sender
 * @sport: Packet source port
 * @daddr: Destination address of packet
 * @dport: Packet destination port
 *
 * This function is the main processing hook of incoming Babel packets. It
 * checks that the packet header is well-formed, then processes the TLVs
 * contained in the packet. This is done in two passes: First all TLVs are
 * parsed into the internal TLV format. If a TLV parser fails, processing of the
 * rest of the packet is aborted.
 *
 * After the parsing step, the TLV handlers are called for each parsed TLV in
 * order.
 */
static void
babel_process_packet(struct babel_iface *ifa,
		     struct babel_pkt_header *pkt, int len,
                     ip_addr saddr, u16 sport,
		     ip_addr daddr, u16 dport)
{
  u8 frame_err UNUSED = 0;
  struct babel_proto *p = ifa->proto;
  struct babel_tlv *tlv;
  struct babel_msg_node *msg;
  list msgs;
  int res;

  int plen = sizeof(struct babel_pkt_header) + get_u16(&pkt->length);
  byte *end = (byte *)pkt + plen;

  struct babel_parse_state state = {
    .get_tlv_data    = &get_packet_tlv_data,
    .get_subtlv_data = &get_packet_subtlv_data,
    .proto           = p,
    .ifa             = ifa,
    .saddr           = saddr,
    .next_hop_ip6    = saddr,
    .sadr_enabled    = babel_sadr_enabled(p),

    /*
     * The core updates current_time() after returning from poll(), so this is
     * actually the time the packet was received, even though there may have
     * been a bit of delay before we got to process it
     */
    .received_time   = current_time(),
  };

  if ((pkt->magic != BABEL_MAGIC) || (pkt->version != BABEL_VERSION))
  {
    TRACE(D_PACKETS, "Strange packet from %I via %s - magic %d version %d",
	  saddr, ifa->iface->name, pkt->magic, pkt->version);
    return;
  }

  if (plen > len)
  {
    LOG_PKT("Bad packet from %I via %s - %s (%u)",
	    saddr, ifa->iface->name, "length mismatch", plen);
    return;
  }

  TRACE(D_PACKETS, "Packet received from %I via %s",
        saddr, ifa->iface->name);

  if (!babel_auth_check(ifa, saddr, sport, daddr, dport, pkt, end, len - plen))
    return;

  init_list(&msgs);

  /* First pass through the packet TLV by TLV, parsing each into internal data
     structures. */
  WALK_TLVS(FIRST_TLV(pkt), end, tlv, frame_err, saddr, ifa->iface->name)
  {
    msg = sl_allocz(p->msg_slab);
    res = babel_read_tlv(tlv, &msg->msg, &state);
    if (res == PARSE_SUCCESS)
    {
      add_tail(&msgs, NODE msg);
    }
    else if (res == PARSE_IGNORE)
    {
      DBG("Babel: Ignoring TLV of type %d\n", tlv->type);
      sl_free(msg);
    }
    else /* PARSE_ERROR */
    {
      LOG_PKT("Bad TLV from %I via %s type %d pos %d - parse error",
	      saddr, ifa->iface->name, tlv->type, (int) ((byte *)tlv - (byte *)pkt));
      sl_free(msg);
      break;
    }
  }
  WALK_TLVS_END;

  /* Parsing done, handle all parsed TLVs, regardless of any errors */
  WALK_LIST_FIRST(msg, msgs)
  {
    if (tlv_data[msg->msg.type].handle_tlv)
      tlv_data[msg->msg.type].handle_tlv(&msg->msg, ifa);
    rem_node(NODE msg);
    sl_free(msg);
  }
}

static void
babel_err_hook(sock *sk, int err)
{
  struct babel_iface *ifa = sk->data;
  struct babel_proto *p = ifa->proto;

  log(L_ERR "%s: Socket error on %s: %M", p->p.name, ifa->iface->name, err);
  /* FIXME: Drop queued TLVs here? */
}


static void
babel_tx_hook(sock *sk)
{
  struct babel_iface *ifa = sk->data;

  DBG("Babel: TX hook called (iface %s, src %I, dst %I)\n",
      sk->iface->name, sk->saddr, sk->daddr);

  babel_send_queue(ifa);
}


static int
babel_rx_hook(sock *sk, uint len)
{
  struct babel_iface *ifa = sk->data;
  struct babel_proto *p = ifa->proto;
  const char *err_dsc = NULL;
  uint err_val = 0;

  if (sk->lifindex != ifa->iface->index)
    return 1;

  DBG("Babel: RX hook called (iface %s, src %I, dst %I)\n",
      sk->iface->name, sk->faddr, sk->laddr);

  /* Silently ignore my own packets */
  if (ipa_equal(sk->faddr, sk->saddr))
    return 1;

  if (!ipa_is_link_local(sk->faddr))
    DROP1("wrong src address");

  if (sk->fport != ifa->cf->port)
    DROP("wrong src port", sk->fport);

  if (len < sizeof(struct babel_pkt_header))
    DROP("too short", len);

  if (sk->flags & SKF_TRUNCATED)
    DROP("truncated", len);

  babel_process_packet(ifa,
		       (struct babel_pkt_header *) sk->rbuf, len,
		       sk->faddr, sk->fport,
		       sk->laddr, sk->dport);
  return 1;

drop:
  LOG_PKT("Bad packet from %I via %s - %s (%u)",
	  sk->faddr, sk->iface->name, err_dsc, err_val);
  return 1;
}

int
babel_open_socket(struct babel_iface *ifa)
{
  struct babel_proto *p = ifa->proto;
  ASSERT_DIE(birdloop_inside(p->p.loop));

  sock *sk;
  sk = sk_new(ifa->pool);
  sk->type = SK_UDP;
  sk->sport = ifa->cf->port;
  sk->dport = ifa->cf->port;
  sk->iface = ifa->iface;
  sk->saddr = ifa->addr;
  sk->vrf = p->p.vrf;

  sk->rx_hook = babel_rx_hook;
  sk->tx_hook = babel_tx_hook;
  sk->err_hook = babel_err_hook;
  sk->data = ifa;

  sk->tos = ifa->cf->tx_tos;
  sk->priority = ifa->cf->tx_priority;
  sk->ttl = 1;
  sk->flags = SKF_LADDR_RX;

  if (sk_open(sk, p->p.loop) < 0)
    goto err;

  if (sk_setup_multicast(sk) < 0)
    goto err;

  if (sk_join_group(sk, IP6_BABEL_ROUTERS) < 0)
    goto err;

  ifa->sk = sk;
  return 1;

err:
  sk_log_error(sk, p->p.name);
  sk_close(sk);
  return 0;
}


/* Authentication checks */
static int
babel_read_pc(struct babel_tlv *hdr, union babel_msg *m UNUSED,
              struct babel_parse_state *state)
{
  struct babel_tlv_pc *tlv = (void *) hdr;

  /* RFC 8967 4.3 (3) - If multiple PCs are found, only the first one is used */
  if (state->auth.pc_seen)
    return PARSE_IGNORE;

  uint index_len = TLV_OPT_LENGTH(tlv);
  if (index_len > BABEL_AUTH_INDEX_LEN)
    return PARSE_IGNORE;

  state->auth.pc = get_u32(&tlv->pc);
  state->auth.pc_seen = 1;
  state->auth.index_len = index_len;
  state->auth.index = tlv->index;
  state->auth.unicast = state->is_unicast;
  state->current_tlv_endpos += index_len;

  return PARSE_SUCCESS;
}

static const struct babel_tlv_data pc_tlv_data = {
  .min_length = sizeof(struct babel_tlv_pc),
  .read_tlv = &babel_read_pc
};

static int
babel_read_challenge_req(struct babel_tlv *hdr, union babel_msg *m UNUSED,
			 struct babel_parse_state *state)
{
  struct babel_tlv_challenge *tlv = (void *) hdr;

  if (!state->is_unicast)
    return PARSE_IGNORE;

  uint nonce_len = TLV_OPT_LENGTH(tlv);
  if (nonce_len > BABEL_AUTH_MAX_NONCE_LEN)
    return PARSE_IGNORE;

  state->auth.challenge_len = nonce_len;
  bmemcpy(state->auth.challenge, tlv->nonce, nonce_len);
  state->auth.challenge_seen = 1;
  state->current_tlv_endpos += nonce_len;

  return PARSE_SUCCESS;
}

static const struct babel_tlv_data challenge_req_tlv_data = {
  .min_length = sizeof(struct babel_tlv_challenge),
  .read_tlv = &babel_read_challenge_req,
};

static int
babel_read_challenge_reply(struct babel_tlv *hdr, union babel_msg *m UNUSED,
                           struct babel_parse_state *state)
{
  struct babel_tlv_challenge *tlv = (void *) hdr;

  if (state->auth.challenge_reply_seen)
    return PARSE_IGNORE;

  uint nonce_len = TLV_OPT_LENGTH(tlv);
  if (nonce_len != BABEL_AUTH_NONCE_LEN)
    return PARSE_IGNORE;

  memcpy(state->auth.challenge_reply, tlv->nonce, BABEL_AUTH_NONCE_LEN);
  state->auth.challenge_reply_seen = 1;
  state->current_tlv_endpos += nonce_len;

  return PARSE_SUCCESS;
}

static const struct babel_tlv_data challenge_reply_tlv_data = {
  .min_length = sizeof(struct babel_tlv_challenge),
  .read_tlv = &babel_read_challenge_reply,
};

static const struct babel_tlv_data *
get_auth_tlv_data(u8 type)
{
  switch (type)
  {
  case BABEL_TLV_PC:
    return &pc_tlv_data;
  case BABEL_TLV_CHALLENGE_REQUEST:
    return &challenge_req_tlv_data;
  case BABEL_TLV_CHALLENGE_REPLY:
    return &challenge_reply_tlv_data;
  default:
    return NULL;
  }
}

uint
babel_auth_write_challenge(struct babel_tlv *hdr, union babel_msg *m,
                           struct babel_write_state *state UNUSED, uint max_len)
{
  struct babel_tlv_challenge *tlv = (void *) hdr;
  struct babel_msg_challenge *msg = &m->challenge;

  uint len = sizeof(struct babel_tlv_challenge) + msg->nonce_len;

  if (len > max_len)
    return 0;

  TLV_HDR(tlv, msg->type, len);
  bmemcpy(tlv->nonce, msg->nonce, msg->nonce_len);

  return len;
}

static void
babel_mac_fill(struct password_item *pass,
	       struct babel_mac_pseudoheader *phdr,
	       byte *pkt, uint pkt_len,
	       byte *mac)
{
  struct mac_context ctx;

  mac_init(&ctx, pass->alg, pass->password, pass->length);
  mac_update(&ctx, (byte *)phdr, sizeof(*phdr));
  mac_update(&ctx, (byte *)pkt, pkt_len);
  memcpy(mac, mac_final(&ctx), mac_get_length(&ctx));
  mac_cleanup(&ctx);
}

static void
babel_mac_build_phdr(struct babel_mac_pseudoheader *phdr,
                     ip_addr saddr, u16 sport,
                     ip_addr daddr, u16 dport)
{
  memset(phdr, 0, sizeof(*phdr));
  put_ip6(phdr->src_addr, saddr);
  put_u16(&phdr->src_port, sport);
  put_ip6(phdr->dst_addr, daddr);
  put_u16(&phdr->dst_port, dport);
  DBG("MAC pseudo-header: %I %d %I %d\n", saddr, sport, daddr, dport);
}

static int
babel_auth_check_mac(struct babel_iface *ifa, byte *pkt,
                     byte *trailer, uint trailer_len,
                     ip_addr saddr, u16 sport,
                     ip_addr daddr, u16 dport)
{
  struct babel_proto *p = ifa->proto;
  uint pkt_len = (uint)(trailer - pkt);
  byte *end = trailer + trailer_len;
  btime now_ = current_real_time();

  if (trailer_len < sizeof(struct babel_tlv))
  {
    LOG_PKT_AUTH("Authentication failed for %I on %s - no MAC signature",
                 saddr, ifa->ifname);
    return 0;
  }

  struct babel_mac_pseudoheader phdr;
  babel_mac_build_phdr(&phdr, saddr, sport, daddr, dport);

  struct password_item *pass;
  WALK_LIST(pass, *ifa->cf->passwords)
  {
    byte mac[MAX_HASH_SIZE];
    uint mac_len = mac_type_length(pass->alg);
    uint frame_err = 0;

    if (pass->accfrom > now_ || pass->accto < now_)
      continue;

    babel_mac_fill(pass, &phdr, pkt, pkt_len, mac);

    struct babel_tlv *tlv0;
    WALK_TLVS((void *)trailer, end, tlv0, frame_err, saddr, ifa->ifname)
    {
      struct babel_tlv_mac *tlv = (void *)tlv0;

      if (tlv->type != BABEL_TLV_MAC)
	continue;

      if ((TLV_OPT_LENGTH(tlv) == mac_len) && !memcmp(tlv->mac, mac, mac_len))
        return 1;

      DBG("MAC mismatch key id %d pos %d len %d/%d\n",
	  pass->id, (int) ((byte *)tlv - (byte *)pkt), mac_len, tlv->length);
    }
    WALK_TLVS_END;

    if (frame_err)
      return 0;
  }

  LOG_PKT_AUTH("Authentication failed for %I on %s - no matching key",
               saddr, ifa->ifname);
  return 0;
}

/**
 * babel_auth_check - Check authentication for a packet
 * @ifa: Interface holding the transmission buffer
 * @saddr: Source address the packet was received from
 * @sport: Source port the packet was received from
 * @daddr: Destination address the packet was sent to
 * @dport: Destination port the packet was sent to
 * @pkt: Pointer to start of the packet data
 * @trailer: Pointer to the packet trailer
 * @trailer_len: Length of the packet trailer
 *
 * This function performs any necessary authentication checks on a packet and
 * returns 0 if the packet should be accepted (either because it has been
 * successfully authenticated or because authentication is disabled or
 * configured in permissive mode), or 1 if the packet should be dropped without
 * further processing.
 */
int
babel_auth_check(struct babel_iface *ifa,
                 ip_addr saddr, u16 sport,
                 ip_addr daddr, u16 dport,
                 struct babel_pkt_header *pkt,
                 byte *trailer, uint trailer_len)
{
  uint frame_err UNUSED = 0;
  struct babel_proto *p = ifa->proto;
  ASSERT_DIE(birdloop_inside(p->p.loop));
  struct babel_tlv *tlv;

  struct babel_parse_state state = {
    .get_tlv_data = &get_auth_tlv_data,
    .proto        = p,
    .ifa          = ifa,
    .saddr        = saddr,
    .is_unicast   = !(ipa_classify(daddr) & IADDR_MULTICAST),
    .auth = {
      .sender = saddr,
    },
  };

  if (ifa->cf->auth_type == BABEL_AUTH_NONE)
    return 1;

  TRACE(D_PACKETS, "Checking packet authentication signature");

  if (!babel_auth_check_mac(ifa, (byte *)pkt,
                           trailer, trailer_len,
                           saddr, sport,
                           daddr, dport))
    goto fail;

  /* MAC verified; parse packet to check packet counter and challenge */
  WALK_TLVS(FIRST_TLV(pkt), trailer, tlv, frame_err, saddr, ifa->ifname)
  {
    union babel_msg msg;
    enum parse_result res;

    res = babel_read_tlv(tlv, &msg, &state);
    if (res == PARSE_ERROR)
    {
      LOG_PKT("Bad TLV from %I via %s type %d pos %d - parse error",
	      saddr, ifa->ifname, tlv->type, (int) ((byte *)tlv - (byte *)pkt));
      goto fail;
    }
  }
  WALK_TLVS_END;

  if (!babel_auth_check_pc(ifa, &state.auth))
    goto fail;

  TRACE(D_PACKETS, "Packet from %I via %s authenticated successfully",
        saddr, ifa->ifname);
  return 1;

fail:
  TRACE(D_PACKETS, "Packet from %I via %s failed authentication%s",
               saddr, ifa->ifname,
               ifa->cf->auth_permissive ? " but accepted in permissive mode" : "");

  return ifa->cf->auth_permissive;
}

/**
 * babel_auth_add_tlvs - Add authentication-related TLVs to a packet
 * @ifa: Interface holding the transmission buffer
 * @tlv: Pointer to the place where any new TLVs should be added
 * @max_len: Maximum length available for adding new TLVs
 *
 * This function adds any new TLVs required by the authentication mode to a
 * packet before it is shipped out. For MAC authentication, this is the packet
 * counter TLV that must be included in every packet.
 */
int
babel_auth_add_tlvs(struct babel_iface *ifa, struct babel_tlv *hdr, uint max_len)
{
  struct babel_proto *p = ifa->proto;
  ASSERT_DIE(birdloop_inside(p->p.loop));
  struct babel_tlv_pc *tlv;
  uint len;

  if (ifa->cf->auth_type == BABEL_AUTH_NONE)
    return 0;

  tlv = (void *) hdr;
  len = sizeof(struct babel_tlv_pc) + BABEL_AUTH_INDEX_LEN;
  max_len += ifa->auth_tx_overhead;

  if (len > max_len)
  {
    LOG_WARN("Insufficient space to add MAC seqno TLV on iface %s: %d < %d",
             ifa->ifname, max_len, len);
    return 0;
  }

  TLV_HDR(tlv, BABEL_TLV_PC, len);
  put_u32(&tlv->pc, ifa->auth_pc++);
  memcpy(tlv->index, ifa->auth_index, BABEL_AUTH_INDEX_LEN);

  /* Reset index on overflow to 0 */
  if (!ifa->auth_pc)
    babel_auth_reset_index(ifa);

  return len;
}

/**
 * babel_auth_sign - Sign an outgoing packet before transmission
 * @ifa: Interface holding the transmission buffer
 * @dest: Destination address of the packet
 *
 * This function adds authentication signature(s) to the packet trailer for each
 * of the configured authentication keys on the interface.
 */
int
babel_auth_sign(struct babel_iface *ifa, ip_addr dest)
{
  struct babel_proto *p = ifa->proto;
  ASSERT_DIE(birdloop_inside(p->p.loop));
  sock *sk = ifa->sk;

  if (ifa->cf->auth_type == BABEL_AUTH_NONE)
    return 0;

  struct babel_pkt_header *hdr = (void *) sk->tbuf;
  int len = get_u16(&hdr->length) + sizeof(struct babel_pkt_header);

  byte *pkt = (byte *) hdr;
  byte *pos = pkt + len;
  byte *end = pkt + ifa->tx_length + ifa->auth_tx_overhead;
  btime now_ = current_real_time();

  struct babel_mac_pseudoheader phdr;
  babel_mac_build_phdr(&phdr, sk->saddr, sk->sport, dest, sk->dport);

  struct password_item *pass;
  WALK_LIST(pass, *ifa->cf->passwords)
  {
    struct babel_tlv_mac *tlv = (void *) pos;
    uint tlv_len = sizeof(struct babel_tlv_mac) + mac_type_length(pass->alg);

    if (pass->genfrom > now_ || pass->gento < now_)
      continue;

    if (pos + tlv_len > end)
    {
      LOG_WARN("Insufficient space for MAC signatures on iface %s dst %I (%d/%d)",
               ifa->ifname, dest, tlv_len, (int) (end-pos));
      break;
    }

    TLV_HDR(tlv, BABEL_TLV_MAC, tlv_len);
    babel_mac_fill(pass, &phdr, pkt, len, tlv->mac);

    pos += tlv_len;
  }

  DBG("Added MAC signatures (%d bytes) on ifa %s for dest %I\n",
      pos - (pkt + len), ifa->ifname, dest);

  return pos - (pkt + len);
}

/**
 * babel_auth_set_tx_overhead - Set interface TX overhead for authentication
 * @ifa: Interface to configure
 *
 * This function sets the TX overhead for an interface based on its
 * authentication configuration.
 */
void
babel_auth_set_tx_overhead(struct babel_iface *ifa)
{
  ASSERT_DIE(birdloop_inside(ifa->proto->p.loop));
  if (ifa->cf->auth_type == BABEL_AUTH_NONE)
  {
    ifa->auth_tx_overhead = 0;
    return;
  }

  ifa->auth_tx_overhead = (sizeof(struct babel_tlv_pc) + BABEL_AUTH_INDEX_LEN +
                           sizeof(struct babel_tlv_mac) * ifa->cf->mac_num_keys +
                           ifa->cf->mac_total_len);
  ifa->tx_length -= ifa->auth_tx_overhead;
}
