server/: Build a proper interface for handling tunnel classes.

[tripe] / server / peer.c

/* -*-c-*-
 *
 * Communication with the peer
 *
 * (c) 2001 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Trivial IP Encryption (TrIPE).
 *
 * TrIPE is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 3 of the License, or (at your
 * option) any later version.
 *
 * TrIPE is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with TrIPE.  If not, see <https://www.gnu.org/licenses/>.
 */

/*----- Header files ------------------------------------------------------*/

#include "tripe.h"

/*----- Global state ------------------------------------------------------*/

udpsocket udpsock[NADDRFAM];

/*----- Static variables --------------------------------------------------*/

static sym_table byname;
static addrmap byaddr;
static unsigned nmobile;
static struct tunnel_node {
  struct tunnel_node *next;
  const tunnel_ops *tops;
} *tunnels, **tunnels_tail = &tunnels;
const tunnel_ops *dflttun;

/*----- Main code ---------------------------------------------------------*/

/* --- @p_pingtype@ --- *
 *
 * Arguments:   @unsigned msg@ = message type
 *
 * Returns:     String to describe the message.
 */

static const char *p_pingtype(unsigned msg)
{
  switch (msg & MSG_TYPEMASK) {
    case MISC_PING:
    case MISC_PONG:
      return "transport-ping";
    case MISC_EPING:
    case MISC_EPONG:
      return "encrypted-ping";
    default:
      abort();
  }
}

/* --- @p_ponged@ --- *
 *
 * Arguments:   @peer *p@ = peer packet arrived from
 *              @unsigned msg@ = message type
 *              @buf *b@ = buffer containing payload
 *
 * Returns:     ---
 *
 * Use:         Processes a ping response.
 */

static void p_ponged(peer *p, unsigned msg, buf *b)
{
  uint32 id;
  const octet *magic;
  ping *pg;

  IF_TRACING(T_PEER, {
    trace(T_PEER, "peer: received %s reply from %s",
          p_pingtype(msg), p->spec.name);
    trace_block(T_PACKET, "peer: ping contents", BBASE(b), BSZ(b));
  })

  if (buf_getu32(b, &id) ||
      (magic = buf_get(b, sizeof(pg->magic))) == 0 ||
      BLEFT(b)) {
    a_warn("PEER", "?PEER", p, "malformed-%s", p_pingtype(msg), A_END);
    return;
  }

  for (pg = p->pings; pg; pg = pg->next) {
    if (pg->id == id)
      goto found;
  }
  a_warn("PEER",
         "?PEER", p,
         "unexpected-%s", p_pingtype(msg),
         "0x%08lx", (unsigned long)id,
         A_END);
  return;

found:
  if (memcmp(magic, pg->magic, sizeof(pg->magic)) != 0) {
    a_warn("PEER", "?PEER", p, "corrupt-%s", p_pingtype(msg), A_END);
    return;
  }
  p_pingdone(pg, PING_OK);
}

/* --- @p_rxupdstats@ --- *
 *
 * Arguments:   @peer *p@ = peer to update
 *              @size_t n@ = size of incoming packet
 *
 * Returns:     ---
 *
 * Use:         Updates the peer's incoming packet statistics.
 */

static void p_rxupdstats(peer *p, size_t n)
{
  p->st.t_last = time(0);
  p->st.n_in++;
  p->st.sz_in += n;
}

/* --- @p_encrypt@ --- *
 *
 * Arguments:   @peer *p@ = peer to encrypt message to
 *              @int ty@ message type to send
 *              @buf *bin, *bout@ = input and output buffers
 *
 * Returns:     ---
 *
 * Use:         Convenience function for packet encryption.  Forces
 *              renegotiation when necessary.  Check for the output buffer
 *              being broken to find out whether the encryption was
 *              successful.
 */

static int p_encrypt(peer *p, int ty, buf *bin, buf *bout)
{
  int err = ksl_encrypt(&p->ks, ty, bin, bout);

  if (err == KSERR_REGEN) {
    kx_start(&p->kx, 1);
    err = 0;
  }
  if (!BOK(bout))
    err = -1;
  return (err);
}

/* --- @p_updateaddr@ --- *
 *
 * Arguments:   @peer *p@ = pointer to peer block
 *              @const addr *a@ = address to associate with this peer
 *
 * Returns:     Zero if the address was changed; @+1@ if it was already
 *              right.
 *
 * Use:         Updates our idea of @p@'s address.
 */

int p_updateaddr(peer *p, const addr *a)
{
  peer *q;
  peer_byaddr *pa, *qa;
  int ix;
  unsigned f;

  /* --- Figure out how to proceed --- *
   *
   * If this address already belongs to a different peer, then swap the
   * addresses over.  This doesn't leave the displaced peer in an especially
   * good state, but it ought to get sorted out soon enough.
   */

  pa = am_find(&byaddr, a, sizeof(peer_byaddr), &f);
  if (f && pa->p == p)
    return (+1);
  else if (!f) {
    T( trace(T_PEER, "peer: updating address for `%s'", p_name(p)); )
    am_remove(&byaddr, p->byaddr);
    p->byaddr = pa; p->spec.sa = *a; pa->p = p;
    p->afix = afix(p->spec.sa.sa.sa_family); assert(p->afix >= 0);
    a_notify("NEWADDR", "?PEER", p, "?ADDR", a, A_END);
    return (0);
  } else {
    q = pa->p; qa = p->byaddr;
    T( trace(T_PEER, "peer: swapping addresses for `%s' and `%s'",
             p_name(p), p_name(q)); )
    q->byaddr = qa; qa->p = q; q->spec.sa = p->spec.sa;
    p->byaddr = pa; pa->p = p; p->spec.sa = *a;
    ix = p->afix; p->afix = q->afix; q->afix = ix;
    a_notify("NEWADDR", "?PEER", p, "?ADDR", a, A_END);
    a_notify("NEWADDR", "?PEER", q, "?ADDR", &q->spec.sa, A_END);
    return (0);
  }
}

/* --- @p_decrypt@ --- *
 *
 * Arguments:   @peer **pp@ = pointer to peer to decrypt message from
 *              @addr *a@ = address the packet arrived on
 *              @size_t n@ = size of original incoming packet
 *              @int ty@ = message type to expect
 *              @buf *bin, *bout@ = input and output buffers
 *
 * Returns:     Zero on success; nonzero on error.
 *
 * Use:         Convenience function for packet decryption.  Reports errors
 *              and updates statistics appropriately.
 *
 *              If @*pp@ is null on entry and there are mobile peers then we
 *              see if any of them can decrypt the packet.  If so, we record
 *              @*a@ as the peer's new address and send a notification.
 */

static int p_decrypt(peer **pp, addr *a, size_t n,
                     int ty, buf *bin, buf *bout)
{
  peer *p, *q;
  int err = KSERR_DECRYPT;

  /* --- If we have a match on the source address then try that first --- */

  q = *pp;
  if (q) {
    T( trace(T_PEER, "peer: decrypting packet from known peer `%s'",
             p_name(q)); )
    if ((err = ksl_decrypt(&q->ks, ty, bin, bout)) != KSERR_DECRYPT ||
        !(q->spec.f & PSF_MOBILE) || nmobile == 1) {
      p = q;
      goto match;
    }
    T( trace(T_PEER, "peer: failed to decrypt: try other mobile peers..."); )
  } else if (nmobile)
    T( trace(T_PEER, "peer: unknown source: trying mobile peers...") );
  else {
    p = 0;
    goto searched;
  }

  /* --- See whether any mobile peer is interested --- */

  p = 0;
  FOREACH_PEER(qq, {
    if (qq == q || !(qq->spec.f & PSF_MOBILE)) continue;
    if ((err = ksl_decrypt(&qq->ks, ty, bin, bout)) == KSERR_DECRYPT) {
      T( trace(T_PEER, "peer: peer `%s' failed to decrypt",
               p_name(qq)); )
        continue;
    } else {
      p = qq;
      IF_TRACING(T_PEER, {
        if (!err)
          trace(T_PEER, "peer: peer `%s' reports success", p_name(qq));
        else {
          trace(T_PEER, "peer: peer `%s' reports decryption error %d",
                p_name(qq), err);
        }
      })
      break;
    }
  });

  /* --- We've searched the mobile peers --- */

searched:
  if (!p) {
    if (!q)
      a_warn("PEER", "-", "unexpected-source", "?ADDR", a, A_END);
    else {
      a_warn("PEER", "?PEER", p, "decrypt-failed",
             "error-code", "%d", err, A_END);
      p_rxupdstats(q, n);
    }
    return (-1);
  }

  /* --- We found one that accepted, so update the peer's address --- */

  if (!err) {
    *pp = p;
    p_updateaddr(p, a);
  }

match:
  p_rxupdstats(p, n);
  if (err) {
    if (p) p->st.n_reject++;
    a_warn("PEER", "?PEER", p, "decrypt-failed",
           "error-code", "%d", err, A_END);
    return (-1);
  }
  if (!BOK(bout))
    return (-1);
  return (0);
}

/* --- @p_read@ --- *
 *
 * Arguments:   @int fd@ = file descriptor to read from
 *              @unsigned mode@ = what happened
 *              @void *v@ = an uninteresting pointer
 *
 * Returns:     ---
 *
 * Use:         Reads a packet from somewhere.
 */

static void p_read(int fd, unsigned mode, void *v)
{
  peer *p = 0;
  addr a;
  socklen_t sz;
  ssize_t n;
  int ch;
  buf b, bb;
#ifndef NTRACE
  int ix = -1;
  char name[NI_MAXHOST], svc[NI_MAXSERV];
#endif

  /* --- Read the data --- */

  QUICKRAND;
  sz = sizeof(addr);
  n = recvfrom(fd, buf_i, sizeof(buf_i), 0, &a.sa, &sz);
  if (n < 0) {
    a_warn("PEER", "-", "socket-read-error", "?ERRNO", A_END);
    return;
  }
  IF_TRACING(T_PEER, {
    ix = afix(a.sa.sa_family);
    getnameinfo(&a.sa, sz, name, sizeof(name), svc, sizeof(svc),
                NI_NUMERICHOST | NI_NUMERICSERV);
  })

  /* --- If the packet is a greeting, don't check peers --- */

  if (n && buf_i[0] == (MSG_MISC | MISC_GREET)) {
    IF_TRACING(T_PEER, {
      trace(T_PEER, "peer: greeting received from %s %s %s",
            aftab[ix].name, name, svc);
      trace_block(T_PACKET, "peer: greeting contents", buf_i, n);
    })
    buf_init(&b, buf_i, n);
    buf_getbyte(&b);
    if (c_check(0, 0, &b) || BLEFT(&b)) {
      a_warn("PEER", "-", "invalid-greeting", A_END);
      return;
    }
    a_notify("GREET",
             "?B64", buf_i + 1, (size_t)(n - 1),
             "?ADDR", &a,
             A_END);
    return;
  }

  /* --- Find the appropriate peer --- *
   *
   * At this stage, don't worry too much about whether we actually found it.
   */

  p = p_findbyaddr(&a);

  IF_TRACING(T_PEER, {
    if (p) {
      trace(T_PEER,
            "peer: packet received from `%s' from address %s %s %s",
            p_name(p), aftab[ix].name, name, svc);
    } else {
      trace(T_PEER, "peer: packet received from unknown address %s %s %s",
            aftab[ix].name, name, svc);
    }
    trace_block(T_PACKET, "peer: packet contents", buf_i, n);
  })

  /* --- Pick the packet apart --- */

  buf_init(&b, buf_i, n);
  if ((ch = buf_getbyte(&b)) < 0) {
    a_warn("PEER", "?PEER", p, "bad-packet", "no-type", A_END);
    return;
  }
  switch (ch & MSG_CATMASK) {
    case MSG_PACKET:
      if (ch & MSG_TYPEMASK) {
        a_warn("PEER",
               "?PEER", p,
               "bad-packet",
               "unknown-type", "0x%02x", ch,
               A_END);
        if (p) p->st.n_reject++;
        return;
      }
      buf_init(&bb, buf_o, sizeof(buf_o));
      if (p_decrypt(&p, &a, n, MSG_PACKET, &b, &bb))
        return;
      if (BOK(&bb)) {
        p->st.n_ipin++;
        p->st.sz_ipin += BSZ(&b);
        p->t->ops->inject(p->t, &bb);
      } else {
        p->st.n_reject++;
        a_warn("PEER", "?PEER", p, "packet-build-failed", A_END);
      }
      break;
    case MSG_KEYEXCH:
      if (p) p_rxupdstats(p, n);
      if (kx_message(p ? &p->kx : 0, &a, ch & MSG_TYPEMASK, &b)) goto unexp;
      break;
    case MSG_MISC:
      switch (ch & MSG_TYPEMASK) {
        case MISC_NOP:
          if (!p) goto unexp;
          p_rxupdstats(p, n);
          T( trace(T_PEER, "peer: received NOP packet"); )
          break;
        case MISC_PING:
          if (!p) goto unexp;
          p_rxupdstats(p, n);
          buf_put(p_txstart(p, MSG_MISC | MISC_PONG), BCUR(&b), BLEFT(&b));
          p_txend(p);
          break;
        case MISC_PONG:
          if (!p) goto unexp;
          p_rxupdstats(p, n);
          p_ponged(p, MISC_PONG, &b);
          break;
        case MISC_EPING:
          buf_init(&bb, buf_t, sizeof(buf_t));
          if (p_decrypt(&p, &a, n, ch, &b, &bb))
            return;
          if (BOK(&bb)) {
            buf_flip(&bb);
            p_encrypt(p, MSG_MISC | MISC_EPONG, &bb,
                      p_txstart(p, MSG_MISC | MISC_EPONG));
            p_txend(p);
          }
          break;
        case MISC_EPONG:
          buf_init(&bb, buf_t, sizeof(buf_t));
          if (p_decrypt(&p, &a, n, ch, &b, &bb))
            return;
          if (BOK(&bb)) {
            buf_flip(&bb);
            p_ponged(p, MISC_EPONG, &bb);
          }
          break;
        case MISC_BYE:
          buf_init(&bb, buf_t, sizeof(buf_t));
          if (p_decrypt(&p, &a, n, ch, &b, &bb)) return;
          if (!(p->spec.f&PSF_EPHEM)) return;
          if (BOK(&bb)) {
            buf_flip(&bb);
            if (BSZ(&bb)) return;
            p_destroy(p, 0);
          }
          break;
      }
      break;
    default:
      if (p) p->st.n_reject++;
      a_warn("PEER",
             "?PEER", p,
             "bad-packet",
             "unknown-category", "0x%02x", ch,
             A_END);
      break;
    unexp:
      a_warn("PEER", "-", "unexpected-source", "?ADDR", &a, A_END);
      break;
  }
}

/* --- @p_txstart@ --- *
 *
 * Arguments:   @peer *p@ = pointer to peer block
 *              @unsigned msg@ = message type code
 *
 * Returns:     A pointer to a buffer to write to.
 *
 * Use:         Starts sending to a peer.  Only one send can happen at a
 *              time.
 */

buf *p_txstart(peer *p, unsigned msg)
{
  buf_init(&p->b, buf_o, sizeof(buf_o));
  buf_putbyte(&p->b, msg);
  return (&p->b);
}

/* --- @p_txaddr@ --- *
 *
 * Arguments:   @const addr *a@ = recipient address
 *              @const void *p@ = pointer to packet to send
 *              @size_t sz@ = length of packet
 *
 * Returns:     Zero if successful, nonzero on error.
 *
 * Use:         Sends a packet to an address which (possibly) isn't a current
 *              peer.
 */

int p_txaddr(const addr *a, const void *p, size_t sz)
{
  socklen_t sasz = addrsz(a);
  int i;

  if ((i = afix(a->sa.sa_family)) < 0) {
    a_warn("PEER", "?ADDR", a, "disabled-address-family", A_END);
    return (-1);
  }
  IF_TRACING(T_PEER, trace_block(T_PACKET, "peer: sending packet", p, sz); )
  if (sendto(udpsock[i].sf.fd, p, sz, 0, &a->sa, sasz) < 0) {
    a_warn("PEER", "?ADDR", a, "socket-write-error", "?ERRNO", A_END);
    return (-1);
  }
  return (0);
}

/* --- @p_txend@ --- *
 *
 * Arguments:   @peer *p@ = pointer to peer block
 *
 * Returns:     ---
 *
 * Use:         Sends a packet to the peer.
 */

static void p_setkatimer(peer *);

static int p_dotxend(peer *p)
{
  socklen_t sasz = addrsz(&p->spec.sa);

  if (!BOK(&p->b)) {
    a_warn("PEER", "?PEER", p, "packet-build-failed", A_END);
    return (0);
  }
  IF_TRACING(T_PEER, trace_block(T_PACKET, "peer: sending packet",
                                 BBASE(&p->b), BLEN(&p->b)); )
  if (sendto(udpsock[p->afix].sf.fd, BBASE(&p->b), BLEN(&p->b),
             0, &p->spec.sa.sa, sasz) < 0) {
    a_warn("PEER", "?PEER", p, "socket-write-error", "?ERRNO", A_END);
    return (0);
  } else {
    p->st.n_out++;
    p->st.sz_out += BLEN(&p->b);
    return (1);
  }
}

void p_txend(peer *p)
{
  if (p_dotxend(p) && p->spec.t_ka) {
    sel_rmtimer(&p->tka);
    p_setkatimer(p);
  }
}

/* --- @p_pingwrite@ --- *
 *
 * Arguments:   @ping *p@ = ping structure
 *              @buf *b@ = buffer to write in
 *
 * Returns:     ---
 *
 * Use:         Fills in a ping structure and writes the packet payload.
 */

static void p_pingwrite(ping *p, buf *b)
{
  static uint32 seq = 0;

  p->id = U32(seq++);
  GR_FILL(&rand_global, p->magic, sizeof(p->magic));
  buf_putu32(b, p->id);
  buf_put(b, p->magic, sizeof(p->magic));
}

/* --- @p_pingdone@ --- *
 *
 * Arguments:   @ping *p@ = ping structure
 *              @int rc@ = return code to pass on
 *
 * Returns:     ---
 *
 * Use:         Disposes of a ping structure, maybe sending a notification.
 */

void p_pingdone(ping *p, int rc)
{
  if (p->prev) p->prev->next = p->next;
  else p->p->pings = p->next;
  if (p->next) p->next->prev = p->prev;
  if (rc != PING_TIMEOUT) sel_rmtimer(&p->t);
  T( trace(T_PEER, "peer: ping 0x%08lx done (rc = %d)",
           (unsigned long)p->id, rc); )
  if (rc >= 0) p->func(rc, p->arg);
}

/* --- @p_pingtimeout@ --- *
 *
 * Arguments:   @struct timeval *now@ = the time now
 *              @void *pv@ = pointer to ping block
 *
 * Returns:     ---
 *
 * Use:         Called when a ping times out.
 */

static void p_pingtimeout(struct timeval *now, void *pv)
{
  ping *p = pv;

  T( trace(T_PEER, "peer: ping 0x%08lx timed out", (unsigned long)p->id); )
  p_pingdone(p, PING_TIMEOUT);
}

/* --- @p_pingsend@ --- *
 *
 * Arguments:   @peer *p@ = destination peer
 *              @ping *pg@ = structure to fill in
 *              @unsigned type@ = message type
 *              @unsigned long timeout@ = how long to wait before giving up
 *              @void (*func)(int, void *)@ = callback function
 *              @void *arg@ = argument for callback
 *
 * Returns:     Zero if successful, nonzero if it failed.
 *
 * Use:         Sends a ping to a peer.  Call @func@ with a nonzero argument
 *              if we get an answer within the timeout, or zero if no answer.
 */

int p_pingsend(peer *p, ping *pg, unsigned type,
               unsigned long timeout,
               void (*func)(int, void *), void *arg)
{
  buf *b, bb;
  struct timeval tv;

  switch (type) {
    case MISC_PING:
      pg->msg = MISC_PONG;
      b = p_txstart(p, MSG_MISC | MISC_PING);
      p_pingwrite(pg, b);
      p_txend(p);
      break;
    case MISC_EPING:
      pg->msg = MISC_EPONG;
      b = p_txstart(p, MSG_MISC | MISC_EPING);
      buf_init(&bb, buf_t, sizeof(buf_t));
      p_pingwrite(pg, &bb);
      buf_flip(&bb);
      p_encrypt(p, MSG_MISC | MISC_EPING, &bb, b);
      if (!BOK(b))
        return (-1);
      p_txend(p);
      break;
    default:
      abort();
      break;
  }

  pg->next = p->pings;
  pg->prev = 0;
  pg->p = p;
  pg->func = func;
  pg->arg = arg;
  if (p->pings) p->pings->prev = pg;
  p->pings = pg;
  gettimeofday(&tv, 0);
  tv.tv_sec += timeout;
  sel_addtimer(&sel, &pg->t, &tv, p_pingtimeout, pg);
  T( trace(T_PEER, "peer: send %s 0x%08lx to %s",
           p_pingtype(type), (unsigned long)pg->id, p->spec.name); )
  return (0);
}

/* --- @p_greet@ --- *
 *
 * Arguments:   @peer *p@ = peer to send to
 *              @const void *c@ = pointer to challenge
 *              @size_t sz@ = size of challenge
 *
 * Returns:     ---
 *
 * Use:         Sends a greeting packet.
 */

void p_greet(peer *p, const void *c, size_t sz)
{
  buf *b = p_txstart(p, MSG_MISC | MISC_GREET);
  buf_put(b, c, sz);
  p_txend(p);
}

/* --- @p_tun@ --- *
 *
 * Arguments:   @peer *p@ = pointer to peer block
 *              @buf *b@ = buffer containing incoming packet
 *
 * Returns:     ---
 *
 * Use:         Handles a packet which needs to be sent to a peer.
 */

void p_tun(peer *p, buf *b)
{
  buf *bb = p_txstart(p, MSG_PACKET);

  QUICKRAND;
  p_encrypt(p, MSG_PACKET, b, bb);
  if (BOK(bb) && BLEN(bb)) {
    p->st.n_ipout++;
    p->st.sz_ipout += BLEN(bb);
    p_txend(p);
  }
}

/* --- @p_keyreload@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Forces a check of the daemon's keyring files.
 */

void p_keyreload(void)
{
  if (km_reload())
    FOREACH_PEER(p, { kx_newkeys(&p->kx); });
}

/* --- @p_interval@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Called periodically to do tidying.
 */

void p_interval(void)
{
  p_keyreload();
  FOREACH_PEER(p, { ksl_prune(&p->ks); });
}

/* --- @p_stats@ --- *
 *
 * Arguments:   @peer *p@ = pointer to a peer block
 *
 * Returns:     A pointer to the peer's statistics.
 */

stats *p_stats(peer *p) { return (&p->st); }

/* --- @p_ifname@ --- *
 *
 * Arguments:   @peer *p@ = pointer to a peer block
 *
 * Returns:     A pointer to the peer's interface name.
 */

const char *p_ifname(peer *p) { return (p->ifname); }

/* --- @p_setifname@ --- *
 *
 * Arguments:   @peer *p@ = pointer to a peer block
 *              @const char *name@ = pointer to the new name
 *
 * Returns:     ---
 *
 * Use:         Changes the name held for a peer's interface.
 */

void p_setifname(peer *p, const char *name)
{
  xfree(p->ifname);
  p->ifname = xstrdup(name);
  if (p->spec.tops->setifname)
    p->spec.tops->setifname(p->t, name);
}

/* --- @p_addr@ --- *
 *
 * Arguments:   @peer *p@ = pointer to a peer block
 *
 * Returns:     A pointer to the peer's address.
 */

const addr *p_addr(peer *p) { return (&p->spec.sa); }

/* --- @p_bind@ --- *
 *
 * Arguments:   @struct addrinfo *ailist@ = addresses to bind to
 *
 * Returns:     ---
 *
 * Use:         Initializes the peer system; creates the socket.
 */

void p_bind(struct addrinfo *ailist)
{
  int fd;
  int len = PKBUFSZ;
  int yes = 1;
  int i;
  struct addrinfo *ai;
  unsigned port, lastport = 0;
  addr a;
  socklen_t sz;

  for (i = 0; i < NADDRFAM; i++) udpsock[i].sf.fd = -1;

  for (ai = ailist; ai; ai = ai->ai_next) {
    if ((i = afix(ai->ai_family)) < 0) continue;
    if (udpsock[i].sf.fd != -1) continue;

    /* --- Note on socket buffer sizes --- *
     *
     * For some bizarre reason, Linux 2.2 (at least) doubles the socket
     * buffer sizes I pass to @setsockopt@.  I'm not putting special-case
     * code here for Linux: BSD (at least TCPv2) does what I tell it rather
     * than second-guessing me.
     */

    if ((fd = socket(ai->ai_family, SOCK_DGRAM, 0)) < 0) {
      a_warn("PEER", "-", "udp-socket", "%s", aftab[i].name,
             "create-failed", "?ERRNO", A_END);
      exit(EXIT_FAILURE);
    }
    if (i == AFIX_INET6 &&
        setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &yes, sizeof(yes))) {
      a_warn("PEER", "-", "udp-socket", "%s", aftab[i].name,
             "set-v6only-failed", "?ERRNO", A_END);
      exit(EXIT_FAILURE);
    }
    assert(ai->ai_addrlen <= sizeof(a));
    memcpy(&a, ai->ai_addr, ai->ai_addrlen);
    if ((port = getport(&a)) == 0 && lastport) setport(&a, lastport);
    if (bind(fd, &a.sa, addrsz(&a))) {
      a_warn("PEER", "-", "udp-socket", "%s", aftab[i].name,
             "bind-failed", "?ERRNO", A_END);
      exit(EXIT_FAILURE);
    }
    if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &len, sizeof(len)) ||
        setsockopt(fd, SOL_SOCKET, SO_SNDBUF, &len, sizeof(len))) {
      a_warn("PEER", "-", "udp-socket", "%s", aftab[i].name,
             "set-buffers-failed", "?ERRNO", A_END);
      exit(EXIT_FAILURE);
    }
    fdflags(fd, O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC);
    if (port)
      udpsock[i].port = port;
    else {
      sz = sizeof(a);
      if (getsockname(fd, &a.sa, &sz)) {
        a_warn("PEER", "-", "udp-socket", "%s", aftab[i].name,
               "read-local-address-failed", "?ERRNO", A_END);
        exit(EXIT_FAILURE);
      }
      udpsock[i].port = lastport = getport(&a);
    }
    T( trace(T_PEER, "peer: created %s socket", aftab[i].name); )
    sel_initfile(&sel, &udpsock[i].sf, fd, SEL_READ, p_read, 0);
    sel_addfile(&udpsock[i].sf);
  }

}

/* --- @p_unbind@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Unbinds the UDP sockets.  There must not be any active peers,
 *              and none can be created until the sockets are rebound.
 */

void p_unbind(void)
{
  int i;

#ifndef NDEBUG
  { peer_iter it; p_mkiter(&it); assert(!p_next(&it)); }
#endif

  for (i = 0; i < NADDRFAM; i++) {
    if (udpsock[i].sf.fd == -1) continue;
    sel_rmfile(&udpsock[i].sf);
    close(udpsock[i].sf.fd);
    udpsock[i].sf.fd = -1;
  }
}

/* --- @p_init@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Initializes the peer system.
 */

void p_init(void)
{
  sym_create(&byname);
  am_create(&byaddr);
}

/* --- @p_addtun@ --- *
 *
 * Arguments:   @const tunnel_ops *tops@ = tunnel ops to add
 *
 * Returns:     ---
 *
 * Use:         Adds a tunnel class to the list of known classes.  If there
 *              is no current default tunnel, then this one is made the
 *              default.
 *
 *              Does nothing if the tunnel class is already known.  So adding
 *              a bunch of tunnels takes quadratic time, but there will be
 *              too few to care about.
 */

void p_addtun(const tunnel_ops *tops)
{
  struct tunnel_node *tn;

  for (tn = tunnels; tn; tn = tn->next)
    if (tn->tops == tops) return;
  tops->init();
  tn = CREATE(struct tunnel_node);
  tn->next = 0; tn->tops = tops;
  *tunnels_tail = tn; tunnels_tail = &tn->next;
  if (!dflttun) dflttun = tops;
}

/* --- @p_setdflttun@ --- *
 *
 * Arguments:   @const tunnel_ops *tops@ = tunnel ops to set
 *
 * Returns:     ---
 *
 * Use:         Sets the default tunnel.  It must already be registered.  The
 *              old default is forgotten.
 */

void p_setdflttun(const tunnel_ops *tops)
  { dflttun = tops; }

/* --- @p_dflttun@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     A pointer to the current default tunnel operations, or null
 *              if no tunnels are defined.
 */

const tunnel_ops *p_dflttun(void) { return (dflttun); }

/* --- @p_findtun@ --- *
 *
 * Arguments:   @const char *name@ = tunnel name
 *
 * Returns:     Pointer to the tunnel operations, or null.
 *
 * Use:         Finds the operations for a named tunnel class.
 */

const tunnel_ops *p_findtun(const char *name)
{
  const struct tunnel_node *tn;

  for (tn = tunnels; tn; tn = tn->next)
    if (mystrieq(tn->tops->name, name) == 0) return (tn->tops);
  return (0);
}

/* --- @p_mktuniter@ --- *
 *
 * Arguments:   @tuniter *i@ = pointer to iterator to initialize
 *
 * Returns:     ---
 *
 * Use:         Initializes a tunnel iterator.
 */

void p_mktuniter(tun_iter *i) { i->next = tunnels; }

/* --- @p_nexttun@ --- *
 *
 * Arguments:   @tuniter *i@ = pointer to iterator
 *
 * Returns:     Pointer to the next tunnel's operations, or null.
 */

const tunnel_ops *p_nexttun(tun_iter *i)
{
  const struct tunnel_node *tn = i->next;

  if (!tn) return (0);
  else { i->next = tn->next; return (tn->tops); }
}

/* --- @p_keepalive@ --- *
 *
 * Arguments:   @struct timeval *now@ = the current time
 *              @void *pv@ = peer to wake up
 *
 * Returns:     ---
 *
 * Use:         Sends a keepalive ping message to its peer.
 */

static void p_keepalive(struct timeval *now, void *pv)
{
  peer *p = pv;

  p_txstart(p, MSG_MISC | MISC_NOP); p_dotxend(p);
  T( trace(T_PEER, "peer: sent keepalive to %s", p->spec.name); )
  p_setkatimer(p);
}

/* --- @p_setkatimer@ --- *
 *
 * Arguments:   @peer *p@ = peer to set
 *
 * Returns:     ---
 *
 * Use:         Resets the keepalive timer thing.
 */

static void p_setkatimer(peer *p)
{
  struct timeval tv;

  if (!p->spec.t_ka)
    return;
  gettimeofday(&tv, 0);
  tv.tv_sec += p->spec.t_ka;
  sel_addtimer(&sel, &p->tka, &tv, p_keepalive, p);
}

/* --- @p_create@ --- *
 *
 * Arguments:   @peerspec *spec@ = information about this peer
 *
 * Returns:     Pointer to the peer block, or null if it failed.
 *
 * Use:         Creates a new named peer block.  No peer is actually attached
 *              by this point.
 */

peer *p_create(peerspec *spec)
{
  peer *p = CREATE(peer);
  const tunnel_ops *tops = spec->tops;
  int fd;
  unsigned f;

  p->byname = sym_find(&byname, spec->name, -1, sizeof(peer_byname), &f);
  if (f) goto tidy_0;
  p->byaddr = am_find(&byaddr, &spec->sa, sizeof(peer_byaddr), &f);
  if (f) goto tidy_1;
  p->byname->p = p->byaddr->p = p;

  T( trace(T_PEER, "peer: creating new peer `%s'", spec->name); )
  p->spec = *spec;
  p->spec.name = (/*unconst*/ char *)SYM_NAME(p->byname);
  if (spec->tag) p->spec.tag = xstrdup(spec->tag);
  if (spec->privtag) p->spec.privtag = xstrdup(spec->privtag);
  if (spec->knock) p->spec.knock = xstrdup(spec->knock);
  p->ks = 0;
  p->pings = 0;
  p->ifname = 0;
  p->afix = afix(p->spec.sa.sa.sa_family); assert(p->afix >= 0);
  memset(&p->st, 0, sizeof(stats));
  p->st.t_start = time(0);
  if (!(tops->flags & TUNF_PRIVOPEN))
    fd = -1;
  else if ((fd = ps_tunfd(tops, &p->ifname)) < 0)
    goto tidy_2;
  if ((p->t = tops->create(p, fd, &p->ifname)) == 0)
    goto tidy_3;
  T( trace(T_TUNNEL, "peer: attached interface %s to peer `%s'",
           p->ifname, p_name(p)); )
  p_setkatimer(p);
  iv_addreason();
  if (kx_setup(&p->kx, p, &p->ks, p->spec.f & PSF_KXMASK))
    goto tidy_4;
  a_notify("ADD",
           "?PEER", p,
           "%s", p->ifname,
           "?ADDR", &p->spec.sa,
           A_END);
  if (!(p->spec.f & KXF_CORK)) {
    a_notify("KXSTART", "?PEER", p, A_END);
    /* Couldn't tell anyone before */
  }
  if (p->spec.f & PSF_MOBILE) nmobile++;
  return (p);

tidy_4:
  if (spec->t_ka) sel_rmtimer(&p->tka);
  xfree(p->ifname);
  p->t->ops->destroy(p->t);
  iv_rmreason();
tidy_3:
  if (fd >= 0) close(fd);
tidy_2:
  am_remove(&byaddr, p->byaddr);
  if (p->spec.tag) xfree(p->spec.tag);
  if (p->spec.privtag) xfree(p->spec.privtag);
tidy_1:
  sym_remove(&byname, p->byname);
tidy_0:
  DESTROY(p);
  return (0);
}

/* --- @p_name@ --- *
 *
 * Arguments:   @peer *p@ = pointer to a peer block
 *
 * Returns:     A pointer to the peer's name.
 */

const char *p_name(peer *p)
  { if (p) return (p->spec.name); else return ("-"); }

/* --- @p_tag@ --- *
 *
 * Arguments:   @peer *p@ = pointer to a peer block
 *
 * Returns:     A pointer to the peer's public key tag.
 */

const char *p_tag(peer *p)
  { return (p->spec.tag ? p->spec.tag : p->spec.name); }

/* --- @p_privtag@ --- *
 *
 * Arguments:   @peer *p@ = pointer to a peer block
 *
 * Returns:     A pointer to the peer's private key tag.
 */

const char *p_privtag(peer *p)
  { return (p->spec.privtag ? p->spec.privtag : tag_priv); }

/* --- @p_spec@ --- *
 *
 * Arguments:   @peer *p@ = pointer to a peer block
 *
 * Returns:     Pointer to the peer's specification
 */

const peerspec *p_spec(peer *p) { return (&p->spec); }

/* --- @p_findbyaddr@ --- *
 *
 * Arguments:   @const addr *a@ = address to look up
 *
 * Returns:     Pointer to the peer block, or null if not found.
 *
 * Use:         Finds a peer by address.
 */

peer *p_findbyaddr(const addr *a)
{
  peer_byaddr *pa;

  if ((pa = am_find(&byaddr, a, 0, 0)) != 0) {
    assert(pa->p);
    return (pa->p);
  }
  return (0);
}

/* --- @p_find@ --- *
 *
 * Arguments:   @const char *name@ = name to look up
 *
 * Returns:     Pointer to the peer block, or null if not found.
 *
 * Use:         Finds a peer by name.
 */

peer *p_find(const char *name)
{
  peer_byname *pn;

  if ((pn = sym_find(&byname, name, -1, 0, 0)) != 0)
    return (pn->p);
  return (0);
}

/* --- @p_destroy@ --- *
 *
 * Arguments:   @peer *p@ = pointer to a peer
 *              @int bye@ = say goodbye to the peer?
 *
 * Returns:     ---
 *
 * Use:         Destroys a peer.
 */

void p_destroy(peer *p, int bye)
{
  ping *pg, *ppg;
  buf *b, bb;

  T( trace(T_PEER, "peer: destroying peer `%s'", p->spec.name); )

  if (bye && (p->spec.f&PSF_EPHEM)) {
    b = p_txstart(p, MSG_MISC | MISC_BYE);
    buf_init(&bb, buf_t, sizeof(buf_t));
    assert(BOK(&bb)); buf_flip(&bb);
    p_encrypt(p, MSG_MISC | MISC_BYE, &bb, b);
    p_txend(p);
  }

  a_notify("KILL", "%s", p->spec.name, A_END);
  ksl_free(&p->ks);
  kx_free(&p->kx);
  if (p->spec.f & PSF_MOBILE) nmobile--;
  if (p->ifname) xfree(p->ifname);
  if (p->spec.tag) xfree(p->spec.tag);
  if (p->spec.privtag) xfree(p->spec.privtag);
  if (p->spec.knock) xfree(p->spec.knock);
  p->t->ops->destroy(p->t);
  if (p->spec.t_ka) sel_rmtimer(&p->tka);
  for (pg = p->pings; pg; pg = ppg) {
    ppg = pg->next;
    p_pingdone(pg, PING_PEERDIED);
  }
  sym_remove(&byname, p->byname);
  am_remove(&byaddr, p->byaddr);
  iv_rmreason();
  DESTROY(p);
}

/* --- @p_destroyall@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Destroys all of the peers, saying goodbye.
 */

void p_destroyall(void) { FOREACH_PEER(p, { p_destroy(p, 1); }); }

/* --- @p_mkiter@ --- *
 *
 * Arguments:   @peer_iter *i@ = pointer to an iterator
 *
 * Returns:     ---
 *
 * Use:         Initializes the iterator.
 */

void p_mkiter(peer_iter *i) { sym_mkiter(&i->i, &byname); }

/* --- @p_next@ --- *
 *
 * Arguments:   @peer_iter *i@ = pointer to an iterator
 *
 * Returns:     Next peer, or null if at the end.
 *
 * Use:         Returns the next peer.
 */

peer *p_next(peer_iter *i)
{
  peer_byname *pn;

  if ((pn = sym_next(&i->i)) == 0)
    return (0);
  return (pn->p);
}

/*----- That's all, folks -------------------------------------------------*/