gvpe/src/vpn_dns.C

/*
    vpn_dns.C -- handle the dns tunnel part of the protocol.
    Copyright (C) 2003-2005 Marc Lehmann <gvpe@schmorp.de>
 
    This file is part of GVPE.

    GVPE 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 2 of the License, or
    (at your option) any later version.
 
    This program 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 gvpe; if not, write to the Free Software
    Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#include "config.h"

#if ENABLE_DNS

// dns processing is EXTREMELY ugly. For obvious(?) reasons.
// it's a hack, use only in emergency situations please.

#include <cstring>

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <sys/uio.h>
#include <errno.h>
#include <time.h>
#include <unistd.h>
#include <fcntl.h>

#include <map>

#include "netcompat.h"

#include "vpn.h"

#define MIN_RETRY 1.
#define MAX_RETRY 60.

#define MAX_OUTSTANDING 40 // max. outstanding requests
#define MAX_WINDOW      100 // max. for MAX_OUTSTANDING
#define MAX_RATE        1000 // requests/s
#define MAX_BACKLOG     (10*1024) // size of protocol backlog, must be > MAXSIZE

#define MAX_DOMAIN_SIZE 220 // 255 is legal limit, but bind doesn't compress well
// 240 leaves about 4 bytes of server reply data
// every two request byte sless give room for one reply byte

// seqno has 12 bits, but the lower bit is always left as zero
// as bind caches ttl=0 records and we have to generate
// sequence numbers that always differ case-insensitively
#define SEQNO_MASK 0x07ff

/*

protocol, in shorthand :)

client -> server <req>  ANY?
server -> client <req>  TXT <rep>

<req> is dns64-encoded <client-id:12><recv-seqno:10>[<send-seqno:10><data>]
<rep> is dns64-encoded <0:12><recv-seqno:10>[<send-seqno:10><data>]

if <client-id> is zero, the connection will be configured:

<0:12><0:4>client-id:12><default-ttl:8><max-size:16><flags:16>

*/

#define MAX_LBL_SIZE 63
#define MAX_PKT_SIZE 512

#define RR_TYPE_TXT 16
#define RR_TYPE_ANY 255
#define RR_CLASS_IN 1

// the "_" is not valid but widely accepted (all octets should be supported, but let's be conservative)
struct dns64
{
  static const char encode_chars[64 + 1];
  static s8 decode_chars[256];

  static int encode_len (int bytes) { return (bytes * 8 + 5) / 6; }
  static int decode_len (int bytes) { return (bytes * 6) / 8; }
  static int encode (char *dst, u8 *src, int len);
  static int decode (u8 *dst, char *src, int len);

  dns64 ();
} dns64;

// the following sequence has been crafted to
// a) look somewhat random
// b) the even (and odd) indices never share the same character as upper/lowercase
const char dns64::encode_chars[64 + 1] = "_-dDpPhHzZrR06QqMmjJkKBb34TtSsvVlL81xXaAeEFf92WwGgYyoO57UucCNniI";
s8 dns64::decode_chars[256];

dns64::dns64 ()
{
  for (int i = 0; i < 64; i++)
    decode_chars [encode_chars [i]] = i + 1;
}

int dns64::encode (char *dst, u8 *src, int len)
{
  // slow, but easy to debug
  char *beg = dst;
  unsigned int accum, bits = 0;

  while (len--)
    {
      accum <<= 8;
      accum  |= *src++;
      bits   += 8;

      while (bits >= 6)
        {
          *dst++ = encode_chars [(accum >> (bits - 6)) & 63];
          bits  -= 6;
        }
    }

  if (bits)
    *dst++ = encode_chars [(accum << (6 - bits)) & 63];

  return dst - beg;
}

int dns64::decode (u8 *dst, char *src, int len)
{
  // slow, but easy to debug
  u8 *beg = dst;
  unsigned int accum, bits = 0;

  while (len--)
    {
      s8 chr = decode_chars [(u8)*src++];

      if (!chr)
        continue;

      accum <<= 6;
      accum  |= chr - 1;
      bits   += 6;

      while (bits >= 8)
        {
          *dst++ = accum >> (bits - 8);
          bits  -= 8;
        }
    }

  return dst - beg;
}

/////////////////////////////////////////////////////////////////////////////

struct byte_stream
{
  u8 *data;
  int maxsize;
  int fill;

  byte_stream (int maxsize);
  ~byte_stream ();

  bool empty () { return !fill; }
  int size () { return fill; }

  bool put (u8 *data, unsigned int datalen);
  bool put (vpn_packet *pkt);
  vpn_packet *get ();

  u8 *begin () { return data; }
  void remove (int count);
};

byte_stream::byte_stream (int maxsize)
: maxsize (maxsize), fill (0)
{
  data = new u8 [maxsize];
}

byte_stream::~byte_stream ()
{
  delete data;
}

void byte_stream::remove (int count)
{
  if (count > fill)
    abort ();

  memmove (data, data + count, fill -= count);
}

bool byte_stream::put (u8 *data, unsigned int datalen)
{
  if (maxsize - fill < datalen)
    return false;

  memcpy (this->data + fill, data, datalen); fill += datalen;

  return true;
}

bool byte_stream::put (vpn_packet *pkt)
{
  if (maxsize - fill < pkt->len + 2)
    return false;

  data [fill++] = pkt->len >> 8;
  data [fill++] = pkt->len;

  memcpy (data + fill, &((*pkt)[0]), pkt->len); fill += pkt->len;

  return true;
}

vpn_packet *byte_stream::get ()
{
  int len = (data [0] << 8) | data [1];

  if (len > MAXSIZE && fill >= 2)
    abort (); // TODO handle this gracefully, connection reset

  if (fill < len + 2)
    return 0;

  vpn_packet *pkt = new vpn_packet;

  pkt->len = len;
  memcpy (&((*pkt)[0]), data + 2, len);
  remove (len + 2);

  return pkt;
}

/////////////////////////////////////////////////////////////////////////////

#define FLAG_QUERY    ( 0 << 15)
#define FLAG_RESPONSE ( 1 << 15)
#define FLAG_OP_MASK  (15 << 14)
#define FLAG_OP_QUERY ( 0 << 11)
#define FLAG_AA       ( 1 << 10)
#define FLAG_TC       ( 1 <<  9)
#define FLAG_RD       ( 1 <<  8)
#define FLAG_RA       ( 1 <<  7)
#define FLAG_AUTH     ( 1 <<  5)
#define FLAG_RCODE_MASK     (15 << 0)
#define FLAG_RCODE_OK       ( 0 << 0)
#define FLAG_RCODE_FORMERR  ( 1 << 0)
#define FLAG_RCODE_SERVFAIL ( 2 << 0)
#define FLAG_RCODE_NXDOMAIN ( 3 << 0)
#define FLAG_RCODE_REFUSED  ( 5 << 0)

#define DEFAULT_CLIENT_FLAGS (FLAG_QUERY | FLAG_OP_QUERY | FLAG_RD)
#define DEFAULT_SERVER_FLAGS (FLAG_RESPONSE | FLAG_OP_QUERY | FLAG_AA | FLAG_RD | FLAG_RA)

struct dns_packet : net_packet
{
  u16 id;
  u16 flags; // QR:1 Opcode:4 AA:1 TC:1 RD:1 RA:1 Z:3 RCODE:4
  u16 qdcount, ancount, nscount, arcount;

  u8 data[MAXSIZE - 6 * 2];

  int decode_label (char *data, int size, int &offs);
};

int dns_packet::decode_label (char *data, int size, int &offs)
{
  char *orig = data;

  memset (data, 0, size);

  while (offs < size - 1)
    {
      u8 len = (*this)[offs++];

      if (!len)
        break;
      else if (len < 64)
        {
          if (size < len + 1 || offs + len >= MAXSIZE - 1)
            break;

          memcpy (data, &((*this)[offs]), len);

          data += len; size -= len; offs += len;
          *data++ = '.'; size--;
        }
      else
        {
          int offs2 = ((len & 63) << 8) + (*this)[offs++];

          data += decode_label (data, size, offs2);
          break;
        }
    }

  return data - orig;
}

/////////////////////////////////////////////////////////////////////////////

struct dns_req
{
  dns_packet *pkt;
  tstamp next;
  int retry;
  connection *conn;
  int seqno;

  dns_req (connection *c);
  void gen_stream_req (int seqno, byte_stream *stream);
};

static u16 dns_id = 12098; // TODO: should be per-vpn

static u16 next_id ()
{
  // the simplest lsfr with periodicity 65535 i could find
  dns_id = (dns_id << 1)
           | (((dns_id >> 1)
               ^ (dns_id >> 2)
               ^ (dns_id >> 4)
               ^ (dns_id >> 15)) & 1);

  return dns_id;
}

dns_req::dns_req (connection *c)
: conn (c)
{
  next = 0;
  retry = 0;

  pkt = new dns_packet;

  pkt->id = next_id ();
}

void dns_req::gen_stream_req (int seqno, byte_stream *stream)
{
  this->seqno = seqno;

  pkt->flags = htons (DEFAULT_CLIENT_FLAGS);
  pkt->qdcount = htons (1);

  int offs = 6*2;
  int dlen = MAX_DOMAIN_SIZE - strlen (THISNODE->domain) - 2;
  // MAX_DOMAIN_SIZE is technically 255, but bind doesn't compress responses well,
  // so we need to have space for 2*MAX_DOMAIN_SIZE + header + extra

  u8 data[256]; //TODO

  data[0] = THISNODE->id; //TODO
  data[1] = seqno >> 7; //TODO
  data[2] = seqno << 1; //TODO

  int datalen = dns64::decode_len (dlen - (dlen + MAX_LBL_SIZE - 1) / MAX_LBL_SIZE) - 3;

  if (datalen > stream->size ())
    datalen = stream->size ();

  char enc[256], *encp = enc;
  
  memcpy (data + 3, stream->begin (), datalen);
  int enclen = dns64::encode (enc, data, datalen + 3);
  stream->remove (datalen);

  while (enclen)
    {
      int lbllen = enclen < MAX_LBL_SIZE ? enclen : MAX_LBL_SIZE;

      (*pkt)[offs++] = lbllen;
      memcpy (pkt->at (offs), encp, lbllen);

      offs += lbllen;
      encp += lbllen;

      enclen -= lbllen;
    }

  const char *suffix = THISNODE->domain;

  // add tunnel domain
  for (;;)
    {
      const char *end = strchr (suffix, '.');

      if (!end)
        end = suffix + strlen (suffix);

      int len = end - suffix;

      (*pkt)[offs++] = len;
      memcpy (&((*pkt)[offs]), suffix, len);
      offs += len;

      if (!*end)
        break;

      suffix = end + 1;
    }

  (*pkt)[offs++] = 0;
  (*pkt)[offs++] = RR_TYPE_ANY >> 8; (*pkt)[offs++] = RR_TYPE_ANY;
  (*pkt)[offs++] = RR_CLASS_IN >> 8; (*pkt)[offs++] = RR_CLASS_IN;

  pkt->len = offs;
}

struct dns_rcv
{
  int seqno;
  dns_packet *pkt; // reply packet
  u8 data [MAXSIZE]; // actually part of the reply packet...
  int datalen;

  dns_rcv (int seqno, u8 *data, int datalen);
  ~dns_rcv ();
};

dns_rcv::dns_rcv (int seqno, u8 *data, int datalen)
: seqno (seqno), pkt (new dns_packet), datalen (datalen)
{
  memcpy (this->data, data, datalen);
}

dns_rcv::~dns_rcv ()
{
  delete pkt;
}

/////////////////////////////////////////////////////////////////////////////

struct dns_cfg
{
  u8 id1, id2, id3;
  u8 def_ttl;
  u8 unused1;
  u16 max_size;
  u8 flags1, flags2;
};

void connection::dnsv4_receive_rep (struct dns_rcv *r)
{
  dns_rcvpq.push_back (r);

  redo:

  for (vector<dns_rcv *>::iterator i = dns_rcvpq.begin ();
       i != dns_rcvpq.end ();
       ++i)
    if (dns_rcvseq == (*i)->seqno)
      {
        dns_rcv *r = *i;

        dns_rcvseq = (dns_rcvseq + 1) & SEQNO_MASK;

        if (!dns_snddq && !dns_rcvdq)
          {
            dns_rcvdq = new byte_stream (MAX_BACKLOG * 2);
            dns_snddq = new byte_stream (MAX_BACKLOG);

            dns_si.set (::conf.dns_forw_host, ::conf.dns_forw_port, PROT_DNSv4);
          }

        if (!dns_rcvdq->put (r->data, r->datalen))
          abort (); // MUST never overflow, can be caused by data corruption, TODO

        while (vpn_packet *pkt = dns_rcvdq->get ())
          {
            sockinfo si;
            si.host = 0; si.port = 0; si.prot = PROT_DNSv4;

            vpn->recv_vpn_packet (pkt, si);
          }
      }
    else if ((u32)(*i)->seqno - (u32)dns_rcvseq + MAX_WINDOW > MAX_WINDOW * 2)
      {
       //D
       //abort();
       printf ("%d erasing %d (%d)\n", THISNODE->id, (u32)(*i)->seqno, dns_rcvseq);
        dns_rcvpq.erase (i);
        goto redo;
      }
}

dns_packet *
vpn::dnsv4_server (dns_packet *pkt)
{
  u16 flags = ntohs (pkt->flags);

  //memcpy (&((*rep)[0]), &((*pkt)[0]), pkt->len);
  int offs = 6 * 2; // skip header

  pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_FORMERR);

  if (!(flags & (FLAG_RESPONSE | FLAG_OP_MASK | FLAG_TC))
      && pkt->qdcount == htons (1))
    {
      char qname[MAXSIZE];
      int qlen = pkt->decode_label ((char *)qname, MAXSIZE - offs, offs);

      u16 qtype  = (*pkt) [offs++] << 8; qtype  |= (*pkt) [offs++];
      u16 qclass = (*pkt) [offs++] << 8; qclass |= (*pkt) [offs++];

      pkt->qdcount = htons (1);
      pkt->ancount = 0;
      pkt->nscount = 0; // should be self, as other nameservers reply like this
      pkt->arcount = 0; // a record for self, as other nameservers reply like this

      pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_NXDOMAIN);

      int dlen = strlen (THISNODE->domain);

      if (qclass == RR_CLASS_IN
          && (qtype == RR_TYPE_ANY || qtype == RR_TYPE_TXT)
          && qlen > dlen + 1
          && !memcmp (qname + qlen - dlen - 1, THISNODE->domain, dlen))
        {
          // correct class, domain: parse
          u8 data[MAXSIZE];
          int datalen = dns64::decode (data, qname, qlen - dlen - 1);

          int client = data[0];
          int seqno  = ((data[1] << 7) | (data[2] >> 1)) & SEQNO_MASK;

          if (0 < client && client <= conns.size ())
            {
              connection *c = conns [client - 1];

              redo:

              for (vector<dns_rcv *>::iterator i = c->dns_rcvpq.begin ();
                   i != c->dns_rcvpq.end ();
                   ++i)
                if ((*i)->seqno == seqno)
                  {
                    // already seen that request: simply reply with the cached reply
                    dns_rcv *r = *i;

                    printf ("DUPLICATE %d\n", htons (r->pkt->id));//D

                    offs = r->pkt->len;
                    memcpy (pkt->at (0), r->pkt->at (0), offs);
                    goto duplicate_request;
                  }

              // new packet, queue
              dns_rcv *rcv = new dns_rcv (seqno, data + 3, datalen - 3);
              c->dnsv4_receive_rep (rcv);

              // now generate reply
              pkt->ancount = htons (1); // one answer RR
              pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_OK);

              (*pkt) [offs++] = 0xc0;
              (*pkt) [offs++] = 6 * 2; // same as in query section

              (*pkt) [offs++] = RR_TYPE_TXT >> 8; (*pkt) [offs++] = RR_TYPE_TXT;
              (*pkt) [offs++] = RR_CLASS_IN >> 8; (*pkt) [offs++] = RR_CLASS_IN;

              (*pkt) [offs++] = 0; (*pkt) [offs++] = 0;
              (*pkt) [offs++] = 0; (*pkt) [offs++] = 0; // TTL

              int dlen = MAX_PKT_SIZE - offs - 2;

              // bind doesn't compress well, so reduce further by one label length
              dlen -= qlen;

              int rdlen_offs = offs += 2;

              while (c->dns_snddq
                     && !c->dns_snddq->empty ()
                     && dlen > 1)
                {
                  int txtlen = dlen <= 255 ? dlen - 1 : 255;

                  if (txtlen > c->dns_snddq->size ())
                    txtlen = c->dns_snddq->size ();

                  (*pkt)[offs++] = txtlen;
                  memcpy (pkt->at (offs), c->dns_snddq->begin (), txtlen);
                  offs += txtlen;
                  c->dns_snddq->remove (txtlen);

                  dlen -= txtlen + 1;
                }

              // avoid empty TXT rdata
              if (offs == rdlen_offs)
                (*pkt)[offs++] = 0;

              int rdlen = offs - rdlen_offs;

              (*pkt) [rdlen_offs - 2] = rdlen >> 8;
              (*pkt) [rdlen_offs - 1] = rdlen;

              // now update dns_rcv copy
              rcv->pkt->len = offs;
              memcpy (rcv->pkt->at (0), pkt->at (0), offs);

              duplicate_request: ;
            }
          else
            pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_FORMERR);
        }

      pkt->len = offs;
    }

  return pkt;
}

void
vpn::dnsv4_client (dns_packet *pkt)
{
  u16 flags = ntohs (pkt->flags);
  int offs = 6 * 2; // skip header

  pkt->qdcount = ntohs (pkt->qdcount);
  pkt->ancount = ntohs (pkt->ancount);

  // go through our request list and find the corresponding request
  for (vector<dns_req *>::iterator i = dns_sndpq.begin ();
       i != dns_sndpq.end ();
       ++i)
    if ((*i)->pkt->id == pkt->id)
      {
        connection *c = (*i)->conn;
        int seqno = (*i)->seqno;
        u8 data[MAXSIZE], *datap = data;

        delete *i;
        dns_sndpq.erase (i);

        if (flags & (FLAG_RESPONSE | FLAG_OP_MASK | FLAG_TC))
          {
            char qname[MAXSIZE];

            while (pkt->qdcount-- && offs < MAXSIZE - 4)
              {
                int qlen = pkt->decode_label ((char *)qname, MAXSIZE - offs, offs);
                offs += 4; // skip qtype, qclass
              }

            while (pkt->ancount-- && offs < MAXSIZE - 10)
              {
                pkt->decode_label ((char *)qname, MAXSIZE - offs, offs);

                u16 qtype  = (*pkt) [offs++] << 8; qtype  |= (*pkt) [offs++];
                u16 qclass = (*pkt) [offs++] << 8; qclass |= (*pkt) [offs++];
                u32 ttl  = (*pkt) [offs++] << 24;
                    ttl |= (*pkt) [offs++] << 16;
                    ttl |= (*pkt) [offs++] <<  8;
                    ttl |= (*pkt) [offs++];

                u16 rdlen = (*pkt) [offs++] << 8; rdlen |= (*pkt) [offs++];

                if (rdlen <= MAXSIZE - offs)
                  {
                    // decode bytes, finally

                    while (rdlen)
                      {
                        int txtlen = (*pkt) [offs++];

                        assert (txtlen + offs < MAXSIZE - 1);

                        memcpy (datap, pkt->at (offs), txtlen);
                        datap += txtlen; offs += txtlen;

                        rdlen -= txtlen + 1;
                      }

                  }

              }
          }

        // todo: pkt now used
        c->dnsv4_receive_rep (new dns_rcv (seqno, data, datap - data));

        break;
      }

  delete pkt;
}

void
vpn::dnsv4_ev (io_watcher &w, short revents)
{
  if (revents & EVENT_READ)
    {
      dns_packet *pkt = new dns_packet;
      struct sockaddr_in sa;
      socklen_t sa_len = sizeof (sa);

      pkt->len = recvfrom (w.fd, &((*pkt)[0]), MAXSIZE, 0, (sockaddr *)&sa, &sa_len);

      if (pkt->len > 0)
        {
          if (pkt->flags & htons (FLAG_TC))
            {
              slog (L_WARN, _("DNS request/response truncated, check protocol settings."));
              //TODO connection reset
            }

          if (THISNODE->dns_port)
            {
              pkt = dnsv4_server (pkt);
              sendto (w.fd, &((*pkt)[0]), pkt->len, 0, (sockaddr *)&sa, sa_len);
            }
          else
            dnsv4_client (pkt);
        }
    }
}

bool
connection::send_dnsv4_packet (vpn_packet *pkt, const sockinfo &si, int tos)
{
  // never initialized
  if (!dns_snddq && !dns_rcvdq)
    {
      dns_rcvdq = new byte_stream (MAX_BACKLOG * 2);
      dns_snddq = new byte_stream (MAX_BACKLOG);

      //dns_rcvseq = dns_sndseq = 0;

      dns_si.set (::conf.dns_forw_host, ::conf.dns_forw_port, PROT_DNSv4);
    }
  
  if (!dns_snddq->put (pkt))
    return false;

  // start timer if neccessary
  if (!THISNODE->dns_port && !dnsv4_tw.active)
    dnsv4_cb (dnsv4_tw);

  return true;
}

void
connection::dnsv4_cb (time_watcher &w)
{
  // check for timeouts and (re)transmit
  tstamp next = NOW + 60;
  dns_req *send = 0;
  
  for (vector<dns_req *>::iterator i = vpn->dns_sndpq.begin ();
       i != vpn->dns_sndpq.end ();
       ++i)
    {
      dns_req *r = *i;

      if (r->next <= NOW)
        {
          if (!send)
            {
              send = r;

              if (r->retry)//D
                printf ("req %d, retry %d\n", r->pkt->id, r->retry);
              r->retry++;
              r->next = NOW + r->retry;
            }
        }

      if (r->next < next)
        next = r->next;
    }

  if (!send
      && vpn->dns_sndpq.size () < MAX_OUTSTANDING)
    {
      send = new dns_req (this);
      send->gen_stream_req (dns_sndseq, dns_snddq);
      vpn->dns_sndpq.push_back (send);

      dns_sndseq = (dns_sndseq + 1) & SEQNO_MASK;
    }

  tstamp min_next = NOW + (1. / (tstamp)MAX_RATE);

  if (send)
    {
      dns_packet *pkt = send->pkt;

      next = min_next;

      sendto (vpn->dnsv4_fd, &((*pkt)[0]), pkt->len, 0, dns_si.sav4 (), dns_si.salenv4 ());
    }
  else if (next < min_next)
    next = min_next;

  w.start (next);
}

#endif

Revision:	1.7
Committed:	Thu Mar 3 16:54:34 2005 UTC (19 years, 2 months ago) by pcg
Content type:	text/plain
Branch:	MAIN
Changes since 1.6:	+5 -3 lines
Log Message:	* empty log message *
#	Content
1	/*
2	vpn_dns.C -- handle the dns tunnel part of the protocol.
3	Copyright (C) 2003-2005 Marc Lehmann <gvpe@schmorp.de>
4
5	This file is part of GVPE.
6
7	GVPE is free software; you can redistribute it and/or modify
8	it under the terms of the GNU General Public License as published by
9	the Free Software Foundation; either version 2 of the License, or
10	(at your option) any later version.
11
12	This program is distributed in the hope that it will be useful,
13	but WITHOUT ANY WARRANTY; without even the implied warranty of
14	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15	GNU General Public License for more details.
16
17	You should have received a copy of the GNU General Public License
18	along with gvpe; if not, write to the Free Software
19	Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
20	*/
21
22	#include "config.h"
23
24	#if ENABLE_DNS
25
26	// dns processing is EXTREMELY ugly. For obvious(?) reasons.
27	// it's a hack, use only in emergency situations please.
28
29	#include <cstring>
30
31	#include <sys/types.h>
32	#include <sys/socket.h>
33	#include <sys/wait.h>
34	#include <sys/uio.h>
35	#include <errno.h>
36	#include <time.h>
37	#include <unistd.h>
38	#include <fcntl.h>
39
40	#include <map>
41
42	#include "netcompat.h"
43
44	#include "vpn.h"
45
46	#define MIN_RETRY 1.
47	#define MAX_RETRY 60.
48
49	#define MAX_OUTSTANDING 40 // max. outstanding requests
50	#define MAX_WINDOW 100 // max. for MAX_OUTSTANDING
51	#define MAX_RATE 1000 // requests/s
52	#define MAX_BACKLOG (10*1024) // size of protocol backlog, must be > MAXSIZE
53
54	#define MAX_DOMAIN_SIZE 220 // 255 is legal limit, but bind doesn't compress well
55	// 240 leaves about 4 bytes of server reply data
56	// every two request byte sless give room for one reply byte
57
58	// seqno has 12 bits, but the lower bit is always left as zero
59	// as bind caches ttl=0 records and we have to generate
60	// sequence numbers that always differ case-insensitively
61	#define SEQNO_MASK 0x07ff
62
63	/*
64
65	protocol, in shorthand :)
66
67	client -> server <req> ANY?
68	server -> client <req> TXT <rep>
69
70	<req> is dns64-encoded <client-id:12><recv-seqno:10>[<send-seqno:10><data>]
71	<rep> is dns64-encoded <0:12><recv-seqno:10>[<send-seqno:10><data>]
72
73	if <client-id> is zero, the connection will be configured:
74
75	<0:12><0:4>client-id:12><default-ttl:8><max-size:16><flags:16>
76
77	*/
78
79	#define MAX_LBL_SIZE 63
80	#define MAX_PKT_SIZE 512
81
82	#define RR_TYPE_TXT 16
83	#define RR_TYPE_ANY 255
84	#define RR_CLASS_IN 1
85
86	// the "_" is not valid but widely accepted (all octets should be supported, but let's be conservative)
87	struct dns64
88	{
89	static const char encode_chars[64 + 1];
90	static s8 decode_chars[256];
91
92	static int encode_len (int bytes) { return (bytes * 8 + 5) / 6; }
93	static int decode_len (int bytes) { return (bytes * 6) / 8; }
94	static int encode (char dst, u8 src, int len);
95	static int decode (u8 dst, char src, int len);
96
97	dns64 ();
98	} dns64;
99
100	// the following sequence has been crafted to
101	// a) look somewhat random
102	// b) the even (and odd) indices never share the same character as upper/lowercase
103	const char dns64::encode_chars[64 + 1] = "_-dDpPhHzZrR06QqMmjJkKBb34TtSsvVlL81xXaAeEFf92WwGgYyoO57UucCNniI";
104	s8 dns64::decode_chars[256];
105
106	dns64::dns64 ()
107	{
108	for (int i = 0; i < 64; i++)
109	decode_chars [encode_chars [i]] = i + 1;
110	}
111
112	int dns64::encode (char dst, u8 src, int len)
113	{
114	// slow, but easy to debug
115	char *beg = dst;
116	unsigned int accum, bits = 0;
117
118	while (len--)
119	{
120	accum <<= 8;
121	accum \|= *src++;
122	bits += 8;
123
124	while (bits >= 6)
125	{
126	*dst++ = encode_chars [(accum >> (bits - 6)) & 63];
127	bits -= 6;
128	}
129	}
130
131	if (bits)
132	*dst++ = encode_chars [(accum << (6 - bits)) & 63];
133
134	return dst - beg;
135	}
136
137	int dns64::decode (u8 dst, char src, int len)
138	{
139	// slow, but easy to debug
140	u8 *beg = dst;
141	unsigned int accum, bits = 0;
142
143	while (len--)
144	{
145	s8 chr = decode_chars [(u8)*src++];
146
147	if (!chr)
148	continue;
149
150	accum <<= 6;
151	accum \|= chr - 1;
152	bits += 6;
153
154	while (bits >= 8)
155	{
156	*dst++ = accum >> (bits - 8);
157	bits -= 8;
158	}
159	}
160
161	return dst - beg;
162	}
163
164	/////////////////////////////////////////////////////////////////////////////
165
166	struct byte_stream
167	{
168	u8 *data;
169	int maxsize;
170	int fill;
171
172	byte_stream (int maxsize);
173	~byte_stream ();
174
175	bool empty () { return !fill; }
176	int size () { return fill; }
177
178	bool put (u8 *data, unsigned int datalen);
179	bool put (vpn_packet *pkt);
180	vpn_packet *get ();
181
182	u8 *begin () { return data; }
183	void remove (int count);
184	};
185
186	byte_stream::byte_stream (int maxsize)
187	: maxsize (maxsize), fill (0)
188	{
189	data = new u8 [maxsize];
190	}
191
192	byte_stream::~byte_stream ()
193	{
194	delete data;
195	}
196
197	void byte_stream::remove (int count)
198	{
199	if (count > fill)
200	abort ();
201
202	memmove (data, data + count, fill -= count);
203	}
204
205	bool byte_stream::put (u8 *data, unsigned int datalen)
206	{
207	if (maxsize - fill < datalen)
208	return false;
209
210	memcpy (this->data + fill, data, datalen); fill += datalen;
211
212	return true;
213	}
214
215	bool byte_stream::put (vpn_packet *pkt)
216	{
217	if (maxsize - fill < pkt->len + 2)
218	return false;
219
220	data [fill++] = pkt->len >> 8;
221	data [fill++] = pkt->len;
222
223	memcpy (data + fill, &((*pkt)[0]), pkt->len); fill += pkt->len;
224
225	return true;
226	}
227
228	vpn_packet *byte_stream::get ()
229	{
230	int len = (data [0] << 8) \| data [1];
231
232	if (len > MAXSIZE && fill >= 2)
233	abort (); // TODO handle this gracefully, connection reset
234
235	if (fill < len + 2)
236	return 0;
237
238	vpn_packet *pkt = new vpn_packet;
239
240	pkt->len = len;
241	memcpy (&((*pkt)[0]), data + 2, len);
242	remove (len + 2);
243
244	return pkt;
245	}
246
247	/////////////////////////////////////////////////////////////////////////////
248
249	#define FLAG_QUERY ( 0 << 15)
250	#define FLAG_RESPONSE ( 1 << 15)
251	#define FLAG_OP_MASK (15 << 14)
252	#define FLAG_OP_QUERY ( 0 << 11)
253	#define FLAG_AA ( 1 << 10)
254	#define FLAG_TC ( 1 << 9)
255	#define FLAG_RD ( 1 << 8)
256	#define FLAG_RA ( 1 << 7)
257	#define FLAG_AUTH ( 1 << 5)
258	#define FLAG_RCODE_MASK (15 << 0)
259	#define FLAG_RCODE_OK ( 0 << 0)
260	#define FLAG_RCODE_FORMERR ( 1 << 0)
261	#define FLAG_RCODE_SERVFAIL ( 2 << 0)
262	#define FLAG_RCODE_NXDOMAIN ( 3 << 0)
263	#define FLAG_RCODE_REFUSED ( 5 << 0)
264
265	#define DEFAULT_CLIENT_FLAGS (FLAG_QUERY \| FLAG_OP_QUERY \| FLAG_RD)
266	#define DEFAULT_SERVER_FLAGS (FLAG_RESPONSE \| FLAG_OP_QUERY \| FLAG_AA \| FLAG_RD \| FLAG_RA)
267
268	struct dns_packet : net_packet
269	{
270	u16 id;
271	u16 flags; // QR:1 Opcode:4 AA:1 TC:1 RD:1 RA:1 Z:3 RCODE:4
272	u16 qdcount, ancount, nscount, arcount;
273
274	u8 data[MAXSIZE - 6 * 2];
275
276	int decode_label (char *data, int size, int &offs);
277	};
278
279	int dns_packet::decode_label (char *data, int size, int &offs)
280	{
281	char *orig = data;
282
283	memset (data, 0, size);
284
285	while (offs < size - 1)
286	{
287	u8 len = (*this)[offs++];
288
289	if (!len)
290	break;
291	else if (len < 64)
292	{
293	if (size < len + 1 \|\| offs + len >= MAXSIZE - 1)
294	break;
295
296	memcpy (data, &((*this)[offs]), len);
297
298	data += len; size -= len; offs += len;
299	*data++ = '.'; size--;
300	}
301	else
302	{
303	int offs2 = ((len & 63) << 8) + (*this)[offs++];
304
305	data += decode_label (data, size, offs2);
306	break;
307	}
308	}
309
310	return data - orig;
311	}
312
313	/////////////////////////////////////////////////////////////////////////////
314
315	struct dns_req
316	{
317	dns_packet *pkt;
318	tstamp next;
319	int retry;
320	connection *conn;
321	int seqno;
322
323	dns_req (connection *c);
324	void gen_stream_req (int seqno, byte_stream *stream);
325	};
326
327	static u16 dns_id = 12098; // TODO: should be per-vpn
328
329	static u16 next_id ()
330	{
331	// the simplest lsfr with periodicity 65535 i could find
332	dns_id = (dns_id << 1)
333	\| (((dns_id >> 1)
334	^ (dns_id >> 2)
335	^ (dns_id >> 4)
336	^ (dns_id >> 15)) & 1);
337
338	return dns_id;
339	}
340
341	dns_req::dns_req (connection *c)
342	: conn (c)
343	{
344	next = 0;
345	retry = 0;
346
347	pkt = new dns_packet;
348
349	pkt->id = next_id ();
350	}
351
352	void dns_req::gen_stream_req (int seqno, byte_stream *stream)
353	{
354	this->seqno = seqno;
355
356	pkt->flags = htons (DEFAULT_CLIENT_FLAGS);
357	pkt->qdcount = htons (1);
358
359	int offs = 6*2;
360	int dlen = MAX_DOMAIN_SIZE - strlen (THISNODE->domain) - 2;
361	// MAX_DOMAIN_SIZE is technically 255, but bind doesn't compress responses well,
362	// so we need to have space for 2*MAX_DOMAIN_SIZE + header + extra
363
364	u8 data[256]; //TODO
365
366	data[0] = THISNODE->id; //TODO
367	data[1] = seqno >> 7; //TODO
368	data[2] = seqno << 1; //TODO
369
370	int datalen = dns64::decode_len (dlen - (dlen + MAX_LBL_SIZE - 1) / MAX_LBL_SIZE) - 3;
371
372	if (datalen > stream->size ())
373	datalen = stream->size ();
374
375	char enc[256], *encp = enc;
376
377	memcpy (data + 3, stream->begin (), datalen);
378	int enclen = dns64::encode (enc, data, datalen + 3);
379	stream->remove (datalen);
380
381	while (enclen)
382	{
383	int lbllen = enclen < MAX_LBL_SIZE ? enclen : MAX_LBL_SIZE;
384
385	(*pkt)[offs++] = lbllen;
386	memcpy (pkt->at (offs), encp, lbllen);
387
388	offs += lbllen;
389	encp += lbllen;
390
391	enclen -= lbllen;
392	}
393
394	const char *suffix = THISNODE->domain;
395
396	// add tunnel domain
397	for (;;)
398	{
399	const char *end = strchr (suffix, '.');
400
401	if (!end)
402	end = suffix + strlen (suffix);
403
404	int len = end - suffix;
405
406	(*pkt)[offs++] = len;
407	memcpy (&((*pkt)[offs]), suffix, len);
408	offs += len;
409
410	if (!*end)
411	break;
412
413	suffix = end + 1;
414	}
415
416	(*pkt)[offs++] = 0;
417	(pkt)[offs++] = RR_TYPE_ANY >> 8; (pkt)[offs++] = RR_TYPE_ANY;
418	(pkt)[offs++] = RR_CLASS_IN >> 8; (pkt)[offs++] = RR_CLASS_IN;
419
420	pkt->len = offs;
421	}
422
423	struct dns_rcv
424	{
425	int seqno;
426	dns_packet *pkt; // reply packet
427	u8 data [MAXSIZE]; // actually part of the reply packet...
428	int datalen;
429
430	dns_rcv (int seqno, u8 *data, int datalen);
431	~dns_rcv ();
432	};
433
434	dns_rcv::dns_rcv (int seqno, u8 *data, int datalen)
435	: seqno (seqno), pkt (new dns_packet), datalen (datalen)
436	{
437	memcpy (this->data, data, datalen);
438	}
439
440	dns_rcv::~dns_rcv ()
441	{
442	delete pkt;
443	}
444
445	/////////////////////////////////////////////////////////////////////////////
446
447	struct dns_cfg
448	{
449	u8 id1, id2, id3;
450	u8 def_ttl;
451	u8 unused1;
452	u16 max_size;
453	u8 flags1, flags2;
454	};
455
456	void connection::dnsv4_receive_rep (struct dns_rcv *r)
457	{
458	dns_rcvpq.push_back (r);
459
460	redo:
461
462	for (vector<dns_rcv *>::iterator i = dns_rcvpq.begin ();
463	i != dns_rcvpq.end ();
464	++i)
465	if (dns_rcvseq == (*i)->seqno)
466	{
467	dns_rcv r = i;
468
469	dns_rcvseq = (dns_rcvseq + 1) & SEQNO_MASK;
470
471	if (!dns_snddq && !dns_rcvdq)
472	{
473	dns_rcvdq = new byte_stream (MAX_BACKLOG * 2);
474	dns_snddq = new byte_stream (MAX_BACKLOG);
475
476	dns_si.set (::conf.dns_forw_host, ::conf.dns_forw_port, PROT_DNSv4);
477	}
478
479	if (!dns_rcvdq->put (r->data, r->datalen))
480	abort (); // MUST never overflow, can be caused by data corruption, TODO
481
482	while (vpn_packet *pkt = dns_rcvdq->get ())
483	{
484	sockinfo si;
485	si.host = 0; si.port = 0; si.prot = PROT_DNSv4;
486
487	vpn->recv_vpn_packet (pkt, si);
488	}
489	}
490	else if ((u32)(i)->seqno - (u32)dns_rcvseq + MAX_WINDOW > MAX_WINDOW 2)
491	{
492	//D
493	//abort();
494	printf ("%d erasing %d (%d)\n", THISNODE->id, (u32)(*i)->seqno, dns_rcvseq);
495	dns_rcvpq.erase (i);
496	goto redo;
497	}
498	}
499
500	dns_packet *
501	vpn::dnsv4_server (dns_packet *pkt)
502	{
503	u16 flags = ntohs (pkt->flags);
504
505	//memcpy (&((rep)[0]), &((pkt)[0]), pkt->len);
506	int offs = 6 * 2; // skip header
507
508	pkt->flags = htons (DEFAULT_SERVER_FLAGS \| FLAG_RCODE_FORMERR);
509
510	if (!(flags & (FLAG_RESPONSE \| FLAG_OP_MASK \| FLAG_TC))
511	&& pkt->qdcount == htons (1))
512	{
513	char qname[MAXSIZE];
514	int qlen = pkt->decode_label ((char *)qname, MAXSIZE - offs, offs);
515
516	u16 qtype = (pkt) [offs++] << 8; qtype \|= (pkt) [offs++];
517	u16 qclass = (pkt) [offs++] << 8; qclass \|= (pkt) [offs++];
518
519	pkt->qdcount = htons (1);
520	pkt->ancount = 0;
521	pkt->nscount = 0; // should be self, as other nameservers reply like this
522	pkt->arcount = 0; // a record for self, as other nameservers reply like this
523
524	pkt->flags = htons (DEFAULT_SERVER_FLAGS \| FLAG_RCODE_NXDOMAIN);
525
526	int dlen = strlen (THISNODE->domain);
527
528	if (qclass == RR_CLASS_IN
529	&& (qtype == RR_TYPE_ANY \|\| qtype == RR_TYPE_TXT)
530	&& qlen > dlen + 1
531	&& !memcmp (qname + qlen - dlen - 1, THISNODE->domain, dlen))
532	{
533	// correct class, domain: parse
534	u8 data[MAXSIZE];
535	int datalen = dns64::decode (data, qname, qlen - dlen - 1);
536
537	int client = data[0];
538	int seqno = ((data[1] << 7) \| (data[2] >> 1)) & SEQNO_MASK;
539
540	if (0 < client && client <= conns.size ())
541	{
542	connection *c = conns [client - 1];
543
544	redo:
545
546	for (vector<dns_rcv *>::iterator i = c->dns_rcvpq.begin ();
547	i != c->dns_rcvpq.end ();
548	++i)
549	if ((*i)->seqno == seqno)
550	{
551	// already seen that request: simply reply with the cached reply
552	dns_rcv r = i;
553
554	printf ("DUPLICATE %d\n", htons (r->pkt->id));//D
555
556	offs = r->pkt->len;
557	memcpy (pkt->at (0), r->pkt->at (0), offs);
558	goto duplicate_request;
559	}
560
561	// new packet, queue
562	dns_rcv *rcv = new dns_rcv (seqno, data + 3, datalen - 3);
563	c->dnsv4_receive_rep (rcv);
564
565	// now generate reply
566	pkt->ancount = htons (1); // one answer RR
567	pkt->flags = htons (DEFAULT_SERVER_FLAGS \| FLAG_RCODE_OK);
568
569	(*pkt) [offs++] = 0xc0;
570	(pkt) [offs++] = 6 2; // same as in query section
571
572	(pkt) [offs++] = RR_TYPE_TXT >> 8; (pkt) [offs++] = RR_TYPE_TXT;
573	(pkt) [offs++] = RR_CLASS_IN >> 8; (pkt) [offs++] = RR_CLASS_IN;
574
575	(pkt) [offs++] = 0; (pkt) [offs++] = 0;
576	(pkt) [offs++] = 0; (pkt) [offs++] = 0; // TTL
577
578	int dlen = MAX_PKT_SIZE - offs - 2;
579
580	// bind doesn't compress well, so reduce further by one label length
581	dlen -= qlen;
582
583	int rdlen_offs = offs += 2;
584
585	while (c->dns_snddq
586	&& !c->dns_snddq->empty ()
587	&& dlen > 1)
588	{
589	int txtlen = dlen <= 255 ? dlen - 1 : 255;
590
591	if (txtlen > c->dns_snddq->size ())
592	txtlen = c->dns_snddq->size ();
593
594	(*pkt)[offs++] = txtlen;
595	memcpy (pkt->at (offs), c->dns_snddq->begin (), txtlen);
596	offs += txtlen;
597	c->dns_snddq->remove (txtlen);
598
599	dlen -= txtlen + 1;
600	}
601
602	// avoid empty TXT rdata
603	if (offs == rdlen_offs)
604	(*pkt)[offs++] = 0;
605
606	int rdlen = offs - rdlen_offs;
607
608	(*pkt) [rdlen_offs - 2] = rdlen >> 8;
609	(*pkt) [rdlen_offs - 1] = rdlen;
610
611	// now update dns_rcv copy
612	rcv->pkt->len = offs;
613	memcpy (rcv->pkt->at (0), pkt->at (0), offs);
614
615	duplicate_request: ;
616	}
617	else
618	pkt->flags = htons (DEFAULT_SERVER_FLAGS \| FLAG_RCODE_FORMERR);
619	}
620
621	pkt->len = offs;
622	}
623
624	return pkt;
625	}
626
627	void
628	vpn::dnsv4_client (dns_packet *pkt)
629	{
630	u16 flags = ntohs (pkt->flags);
631	int offs = 6 * 2; // skip header
632
633	pkt->qdcount = ntohs (pkt->qdcount);
634	pkt->ancount = ntohs (pkt->ancount);
635
636	// go through our request list and find the corresponding request
637	for (vector<dns_req *>::iterator i = dns_sndpq.begin ();
638	i != dns_sndpq.end ();
639	++i)
640	if ((*i)->pkt->id == pkt->id)
641	{
642	connection c = (i)->conn;
643	int seqno = (*i)->seqno;
644	u8 data[MAXSIZE], *datap = data;
645
646	delete *i;
647	dns_sndpq.erase (i);
648
649	if (flags & (FLAG_RESPONSE \| FLAG_OP_MASK \| FLAG_TC))
650	{
651	char qname[MAXSIZE];
652
653	while (pkt->qdcount-- && offs < MAXSIZE - 4)
654	{
655	int qlen = pkt->decode_label ((char *)qname, MAXSIZE - offs, offs);
656	offs += 4; // skip qtype, qclass
657	}
658
659	while (pkt->ancount-- && offs < MAXSIZE - 10)
660	{
661	pkt->decode_label ((char *)qname, MAXSIZE - offs, offs);
662
663	u16 qtype = (pkt) [offs++] << 8; qtype \|= (pkt) [offs++];
664	u16 qclass = (pkt) [offs++] << 8; qclass \|= (pkt) [offs++];
665	u32 ttl = (*pkt) [offs++] << 24;
666	ttl \|= (*pkt) [offs++] << 16;
667	ttl \|= (*pkt) [offs++] << 8;
668	ttl \|= (*pkt) [offs++];
669
670	u16 rdlen = (pkt) [offs++] << 8; rdlen \|= (pkt) [offs++];
671
672	if (rdlen <= MAXSIZE - offs)
673	{
674	// decode bytes, finally
675
676	while (rdlen)
677	{
678	int txtlen = (*pkt) [offs++];
679
680	assert (txtlen + offs < MAXSIZE - 1);
681
682	memcpy (datap, pkt->at (offs), txtlen);
683	datap += txtlen; offs += txtlen;
684
685	rdlen -= txtlen + 1;
686	}
687
688	}
689
690	}
691	}
692
693	// todo: pkt now used
694	c->dnsv4_receive_rep (new dns_rcv (seqno, data, datap - data));
695
696	break;
697	}
698
699	delete pkt;
700	}
701
702	void
703	vpn::dnsv4_ev (io_watcher &w, short revents)
704	{
705	if (revents & EVENT_READ)
706	{
707	dns_packet *pkt = new dns_packet;
708	struct sockaddr_in sa;
709	socklen_t sa_len = sizeof (sa);
710
711	pkt->len = recvfrom (w.fd, &((pkt)[0]), MAXSIZE, 0, (sockaddr )&sa, &sa_len);
712
713	if (pkt->len > 0)
714	{
715	if (pkt->flags & htons (FLAG_TC))
716	{
717	slog (L_WARN, _("DNS request/response truncated, check protocol settings."));
718	//TODO connection reset
719	}
720
721	if (THISNODE->dns_port)
722	{
723	pkt = dnsv4_server (pkt);
724	sendto (w.fd, &((pkt)[0]), pkt->len, 0, (sockaddr )&sa, sa_len);
725	}
726	else
727	dnsv4_client (pkt);
728	}
729	}
730	}
731
732	bool
733	connection::send_dnsv4_packet (vpn_packet *pkt, const sockinfo &si, int tos)
734	{
735	// never initialized
736	if (!dns_snddq && !dns_rcvdq)
737	{
738	dns_rcvdq = new byte_stream (MAX_BACKLOG * 2);
739	dns_snddq = new byte_stream (MAX_BACKLOG);
740
741	//dns_rcvseq = dns_sndseq = 0;
742
743	dns_si.set (::conf.dns_forw_host, ::conf.dns_forw_port, PROT_DNSv4);
744	}
745
746	if (!dns_snddq->put (pkt))
747	return false;
748
749	// start timer if neccessary
750	if (!THISNODE->dns_port && !dnsv4_tw.active)
751	dnsv4_cb (dnsv4_tw);
752
753	return true;
754	}
755
756	void
757	connection::dnsv4_cb (time_watcher &w)
758	{
759	// check for timeouts and (re)transmit
760	tstamp next = NOW + 60;
761	dns_req *send = 0;
762
763	for (vector<dns_req *>::iterator i = vpn->dns_sndpq.begin ();
764	i != vpn->dns_sndpq.end ();
765	++i)
766	{
767	dns_req r = i;
768
769	if (r->next <= NOW)
770	{
771	if (!send)
772	{
773	send = r;
774
775	if (r->retry)//D
776	printf ("req %d, retry %d\n", r->pkt->id, r->retry);
777	r->retry++;
778	r->next = NOW + r->retry;
779	}
780	}
781
782	if (r->next < next)
783	next = r->next;
784	}
785
786	if (!send
787	&& vpn->dns_sndpq.size () < MAX_OUTSTANDING)
788	{
789	send = new dns_req (this);
790	send->gen_stream_req (dns_sndseq, dns_snddq);
791	vpn->dns_sndpq.push_back (send);
792
793	dns_sndseq = (dns_sndseq + 1) & SEQNO_MASK;
794	}
795
796	tstamp min_next = NOW + (1. / (tstamp)MAX_RATE);
797
798	if (send)
799	{
800	dns_packet *pkt = send->pkt;
801
802	next = min_next;
803
804	sendto (vpn->dnsv4_fd, &((*pkt)[0]), pkt->len, 0, dns_si.sav4 (), dns_si.salenv4 ());
805	}
806	else if (next < min_next)
807	next = min_next;
808
809	w.start (next);
810	}
811
812	#endif
813