gvpe/src/vpn_dns.C

/*
    vpn_dns.C -- handle the dns tunnel part of the protocol.
    Copyright (C) 2003-2004 Marc Lehmann <pcg@goof.com>
 
    This program 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 this program; 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

#define SEQNO_MASK 0xffff

/*

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;

const char dns64::encode_chars[64 + 1] = "_4B9dLphHzrqQmGjkTbJt5svlZX8xSaReEYfwKgF1DP2W6NyVOU70IouACcMn3i-";
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];

  printf ("get len %d, fill %d\n", len, fill);//D

  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 >> 8; //TODO
  data[2] = seqno; //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, dns_packet *req, u8 *data, int datalen);
  ~dns_rcv ();
};

dns_rcv::dns_rcv (int seqno, dns_packet *req, u8 *data, int datalen)
: seqno (seqno), pkt (new dns_packet), datalen (datalen)
{
  memcpy (this->data, data, datalen);
  pkt->len = req->len;
  memcpy (pkt->at (0), req->at (0), req->len);
}

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)dns_rcvseq - MAX_WINDOW - (u32)(*i)->seqno < MAX_WINDOW * 2)
      {
        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] << 8) | data[2]) & SEQNO_MASK;

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

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

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

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

              // 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;

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

  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;
                      }

                  }

              }
          }

        if (datap != data)
          printf ("%02x %02x %02x %02x\n",
              data[0],
              data[1],
              data[2],
              data[3]);

        printf ("recv %d,%d\n", pkt->id, seqno, datap - data);//D
        c->dnsv4_receive_rep (new dns_rcv (seqno, pkt, 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:	1.5
Committed:	Thu Mar 3 07:24:57 2005 UTC (19 years, 2 months ago) by pcg
Content type:	text/plain
Branch:	MAIN
Changes since 1.4:	+258 -104 lines
Log Message:	* empty log message *
#	Content
1	/*
2	vpn_dns.C -- handle the dns tunnel part of the protocol.
3	Copyright (C) 2003-2004 Marc Lehmann <pcg@goof.com>
4
5	This program is free software; you can redistribute it and/or modify
6	it under the terms of the GNU General Public License as published by
7	the Free Software Foundation; either version 2 of the License, or
8	(at your option) any later version.
9
10	This program is distributed in the hope that it will be useful,
11	but WITHOUT ANY WARRANTY; without even the implied warranty of
12	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13	GNU General Public License for more details.
14
15	You should have received a copy of the GNU General Public License
16	along with this program; if not, write to the Free Software
17	Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18	*/
19
20	#include "config.h"
21
22	#if ENABLE_DNS
23
24	// dns processing is EXTREMELY ugly. For obvious(?) reasons.
25	// it's a hack, use only in emergency situations please.
26
27	#include <cstring>
28
29	#include <sys/types.h>
30	#include <sys/socket.h>
31	#include <sys/wait.h>
32	#include <sys/uio.h>
33	#include <errno.h>
34	#include <time.h>
35	#include <unistd.h>
36	#include <fcntl.h>
37
38	#include <map>
39
40	#include "netcompat.h"
41
42	#include "vpn.h"
43
44	#define MIN_RETRY 1.
45	#define MAX_RETRY 60.
46
47	#define MAX_OUTSTANDING 40 // max. outstanding requests
48	#define MAX_WINDOW 100 // max. for MAX_OUTSTANDING
49	#define MAX_RATE 1000 // requests/s
50	#define MAX_BACKLOG (10*1024) // size of protocol backlog, must be > MAXSIZE
51
52	#define MAX_DOMAIN_SIZE 220 // 255 is legal limit, but bind doesn't compress well
53	// 240 leaves about 4 bytes of server reply data
54	// every two request byte sless give room for one reply byte
55
56	#define SEQNO_MASK 0xffff
57
58	/*
59
60	protocol, in shorthand :)
61
62	client -> server <req> ANY?
63	server -> client <req> TXT <rep>
64
65	<req> is dns64-encoded <client-id:12><recv-seqno:10>[<send-seqno:10><data>]
66	<rep> is dns64-encoded <0:12><recv-seqno:10>[<send-seqno:10><data>]
67
68	if <client-id> is zero, the connection will be configured:
69
70	<0:12><0:4>client-id:12><default-ttl:8><max-size:16><flags:16>
71
72	*/
73
74	#define MAX_LBL_SIZE 63
75	#define MAX_PKT_SIZE 512
76
77	#define RR_TYPE_TXT 16
78	#define RR_TYPE_ANY 255
79	#define RR_CLASS_IN 1
80
81	// the "_" is not valid but widely accepted (all octets should be supported, but let's be conservative)
82	struct dns64
83	{
84	static const char encode_chars[64 + 1];
85	static s8 decode_chars[256];
86
87	static int encode_len (int bytes) { return (bytes * 8 + 5) / 6; }
88	static int decode_len (int bytes) { return (bytes * 6) / 8; }
89	static int encode (char dst, u8 src, int len);
90	static int decode (u8 dst, char src, int len);
91
92	dns64 ();
93	} dns64;
94
95	const char dns64::encode_chars[64 + 1] = "_4B9dLphHzrqQmGjkTbJt5svlZX8xSaReEYfwKgF1DP2W6NyVOU70IouACcMn3i-";
96	s8 dns64::decode_chars[256];
97
98	dns64::dns64 ()
99	{
100	for (int i = 0; i < 64; i++)
101	decode_chars [encode_chars [i]] = i + 1;
102	}
103
104	int dns64::encode (char dst, u8 src, int len)
105	{
106	// slow, but easy to debug
107	char *beg = dst;
108	unsigned int accum, bits = 0;
109
110	while (len--)
111	{
112	accum <<= 8;
113	accum \|= *src++;
114	bits += 8;
115
116	while (bits >= 6)
117	{
118	*dst++ = encode_chars [(accum >> (bits - 6)) & 63];
119	bits -= 6;
120	}
121	}
122
123	if (bits)
124	*dst++ = encode_chars [(accum << (6 - bits)) & 63];
125
126	return dst - beg;
127	}
128
129	int dns64::decode (u8 dst, char src, int len)
130	{
131	// slow, but easy to debug
132	u8 *beg = dst;
133	unsigned int accum, bits = 0;
134
135	while (len--)
136	{
137	s8 chr = decode_chars [(u8)*src++];
138
139	if (!chr)
140	continue;
141
142	accum <<= 6;
143	accum \|= chr - 1;
144	bits += 6;
145
146	while (bits >= 8)
147	{
148	*dst++ = accum >> (bits - 8);
149	bits -= 8;
150	}
151	}
152
153	return dst - beg;
154	}
155
156	/////////////////////////////////////////////////////////////////////////////
157
158	struct byte_stream
159	{
160	u8 *data;
161	int maxsize;
162	int fill;
163
164	byte_stream (int maxsize);
165	~byte_stream ();
166
167	bool empty () { return !fill; }
168	int size () { return fill; }
169
170	bool put (u8 *data, unsigned int datalen);
171	bool put (vpn_packet *pkt);
172	vpn_packet *get ();
173
174	u8 *begin () { return data; }
175	void remove (int count);
176	};
177
178	byte_stream::byte_stream (int maxsize)
179	: maxsize (maxsize), fill (0)
180	{
181	data = new u8 [maxsize];
182	}
183
184	byte_stream::~byte_stream ()
185	{
186	delete data;
187	}
188
189	void byte_stream::remove (int count)
190	{
191	if (count > fill)
192	abort ();
193
194	memmove (data, data + count, fill -= count);
195	}
196
197	bool byte_stream::put (u8 *data, unsigned int datalen)
198	{
199	if (maxsize - fill < datalen)
200	return false;
201
202	memcpy (this->data + fill, data, datalen); fill += datalen;
203
204	return true;
205	}
206
207	bool byte_stream::put (vpn_packet *pkt)
208	{
209	if (maxsize - fill < pkt->len + 2)
210	return false;
211
212	data [fill++] = pkt->len >> 8;
213	data [fill++] = pkt->len;
214
215	memcpy (data + fill, &((*pkt)[0]), pkt->len); fill += pkt->len;
216
217	return true;
218	}
219
220	vpn_packet *byte_stream::get ()
221	{
222	int len = (data [0] << 8) \| data [1];
223
224	printf ("get len %d, fill %d\n", len, fill);//D
225
226	if (len > MAXSIZE && fill >= 2)
227	abort (); // TODO handle this gracefully, connection reset
228
229	if (fill < len + 2)
230	return 0;
231
232	vpn_packet *pkt = new vpn_packet;
233
234	pkt->len = len;
235	memcpy (&((*pkt)[0]), data + 2, len);
236	remove (len + 2);
237
238	return pkt;
239	}
240
241	/////////////////////////////////////////////////////////////////////////////
242
243	#define FLAG_QUERY ( 0 << 15)
244	#define FLAG_RESPONSE ( 1 << 15)
245	#define FLAG_OP_MASK (15 << 14)
246	#define FLAG_OP_QUERY ( 0 << 11)
247	#define FLAG_AA ( 1 << 10)
248	#define FLAG_TC ( 1 << 9)
249	#define FLAG_RD ( 1 << 8)
250	#define FLAG_RA ( 1 << 7)
251	#define FLAG_AUTH ( 1 << 5)
252	#define FLAG_RCODE_MASK (15 << 0)
253	#define FLAG_RCODE_OK ( 0 << 0)
254	#define FLAG_RCODE_FORMERR ( 1 << 0)
255	#define FLAG_RCODE_SERVFAIL ( 2 << 0)
256	#define FLAG_RCODE_NXDOMAIN ( 3 << 0)
257	#define FLAG_RCODE_REFUSED ( 5 << 0)
258
259	#define DEFAULT_CLIENT_FLAGS (FLAG_QUERY \| FLAG_OP_QUERY \| FLAG_RD)
260	#define DEFAULT_SERVER_FLAGS (FLAG_RESPONSE \| FLAG_OP_QUERY \| FLAG_AA \| FLAG_RD \| FLAG_RA)
261
262	struct dns_packet : net_packet
263	{
264	u16 id;
265	u16 flags; // QR:1 Opcode:4 AA:1 TC:1 RD:1 RA:1 Z:3 RCODE:4
266	u16 qdcount, ancount, nscount, arcount;
267
268	u8 data[MAXSIZE - 6 * 2];
269
270	int decode_label (char *data, int size, int &offs);
271	};
272
273	int dns_packet::decode_label (char *data, int size, int &offs)
274	{
275	char *orig = data;
276
277	memset (data, 0, size);
278
279	while (offs < size - 1)
280	{
281	u8 len = (*this)[offs++];
282
283	if (!len)
284	break;
285	else if (len < 64)
286	{
287	if (size < len + 1 \|\| offs + len >= MAXSIZE - 1)
288	break;
289
290	memcpy (data, &((*this)[offs]), len);
291
292	data += len; size -= len; offs += len;
293	*data++ = '.'; size--;
294	}
295	else
296	{
297	int offs2 = ((len & 63) << 8) + (*this)[offs++];
298
299	data += decode_label (data, size, offs2);
300	break;
301	}
302	}
303
304	return data - orig;
305	}
306
307	/////////////////////////////////////////////////////////////////////////////
308
309	struct dns_req
310	{
311	dns_packet *pkt;
312	tstamp next;
313	int retry;
314	connection *conn;
315	int seqno;
316
317	dns_req (connection *c);
318	void gen_stream_req (int seqno, byte_stream *stream);
319	};
320
321	static u16 dns_id = 12098; // TODO: should be per-vpn
322
323	static u16 next_id ()
324	{
325	// the simplest lsfr with periodicity 65535 i could find
326	dns_id = (dns_id << 1)
327	\| (((dns_id >> 1)
328	^ (dns_id >> 2)
329	^ (dns_id >> 4)
330	^ (dns_id >> 15)) & 1);
331
332	return dns_id;
333	}
334
335	dns_req::dns_req (connection *c)
336	: conn (c)
337	{
338	next = 0;
339	retry = 0;
340
341	pkt = new dns_packet;
342
343	pkt->id = next_id ();
344	}
345
346	void dns_req::gen_stream_req (int seqno, byte_stream *stream)
347	{
348	this->seqno = seqno;
349
350	pkt->flags = htons (DEFAULT_CLIENT_FLAGS);
351	pkt->qdcount = htons (1);
352
353	int offs = 6*2;
354	int dlen = MAX_DOMAIN_SIZE - strlen (THISNODE->domain) - 2;
355	// MAX_DOMAIN_SIZE is technically 255, but bind doesn't compress responses well,
356	// so we need to have space for 2*MAX_DOMAIN_SIZE + header + extra
357
358	u8 data[256]; //TODO
359
360	data[0] = THISNODE->id; //TODO
361	data[1] = seqno >> 8; //TODO
362	data[2] = seqno; //TODO
363
364	int datalen = dns64::decode_len (dlen - (dlen + MAX_LBL_SIZE - 1) / MAX_LBL_SIZE) - 3;
365
366	if (datalen > stream->size ())
367	datalen = stream->size ();
368
369	char enc[256], *encp = enc;
370
371	memcpy (data + 3, stream->begin (), datalen);
372	int enclen = dns64::encode (enc, data, datalen + 3);
373	stream->remove (datalen);
374
375	while (enclen)
376	{
377	int lbllen = enclen < MAX_LBL_SIZE ? enclen : MAX_LBL_SIZE;
378
379	(*pkt)[offs++] = lbllen;
380	memcpy (pkt->at (offs), encp, lbllen);
381
382	offs += lbllen;
383	encp += lbllen;
384
385	enclen -= lbllen;
386	}
387
388	const char *suffix = THISNODE->domain;
389
390	// add tunnel domain
391	for (;;)
392	{
393	const char *end = strchr (suffix, '.');
394
395	if (!end)
396	end = suffix + strlen (suffix);
397
398	int len = end - suffix;
399
400	(*pkt)[offs++] = len;
401	memcpy (&((*pkt)[offs]), suffix, len);
402	offs += len;
403
404	if (!*end)
405	break;
406
407	suffix = end + 1;
408	}
409
410	(*pkt)[offs++] = 0;
411	(pkt)[offs++] = RR_TYPE_ANY >> 8; (pkt)[offs++] = RR_TYPE_ANY;
412	(pkt)[offs++] = RR_CLASS_IN >> 8; (pkt)[offs++] = RR_CLASS_IN;
413
414	pkt->len = offs;
415	}
416
417	struct dns_rcv
418	{
419	int seqno;
420	dns_packet *pkt; // reply packet
421	u8 data [MAXSIZE]; // actually part of the reply packet...
422	int datalen;
423
424	dns_rcv (int seqno, dns_packet req, u8 data, int datalen);
425	~dns_rcv ();
426	};
427
428	dns_rcv::dns_rcv (int seqno, dns_packet req, u8 data, int datalen)
429	: seqno (seqno), pkt (new dns_packet), datalen (datalen)
430	{
431	memcpy (this->data, data, datalen);
432	pkt->len = req->len;
433	memcpy (pkt->at (0), req->at (0), req->len);
434	}
435
436	dns_rcv::~dns_rcv ()
437	{
438	delete pkt;
439	}
440
441	/////////////////////////////////////////////////////////////////////////////
442
443	struct dns_cfg
444	{
445	u8 id1, id2, id3;
446	u8 def_ttl;
447	u8 unused1;
448	u16 max_size;
449	u8 flags1, flags2;
450	};
451
452	void connection::dnsv4_receive_rep (struct dns_rcv *r)
453	{
454	dns_rcvpq.push_back (r);
455
456	redo:
457
458	for (vector<dns_rcv *>::iterator i = dns_rcvpq.begin ();
459	i != dns_rcvpq.end ();
460	++i)
461	if (dns_rcvseq == (*i)->seqno)
462	{
463	dns_rcv r = i;
464
465	dns_rcvseq = (dns_rcvseq + 1) & SEQNO_MASK;
466
467	if (!dns_snddq && !dns_rcvdq)
468	{
469	dns_rcvdq = new byte_stream (MAX_BACKLOG * 2);
470	dns_snddq = new byte_stream (MAX_BACKLOG);
471
472	dns_si.set (::conf.dns_forw_host, ::conf.dns_forw_port, PROT_DNSv4);
473	}
474
475	if (!dns_rcvdq->put (r->data, r->datalen))
476	abort (); // MUST never overflow, can be caused by data corruption, TODO
477
478	while (vpn_packet *pkt = dns_rcvdq->get ())
479	{
480	sockinfo si;
481	si.host = 0; si.port = 0; si.prot = PROT_DNSv4;
482
483	vpn->recv_vpn_packet (pkt, si);
484	}
485	}
486	else if ((u32)dns_rcvseq - MAX_WINDOW - (u32)(i)->seqno < MAX_WINDOW 2)
487	{
488	dns_rcvpq.erase (i);
489	goto redo;
490	}
491	}
492
493	dns_packet *
494	vpn::dnsv4_server (dns_packet *pkt)
495	{
496	u16 flags = ntohs (pkt->flags);
497
498	//memcpy (&((rep)[0]), &((pkt)[0]), pkt->len);
499	int offs = 6 * 2; // skip header
500
501	pkt->flags = htons (DEFAULT_SERVER_FLAGS \| FLAG_RCODE_FORMERR);
502
503	if (!(flags & (FLAG_RESPONSE \| FLAG_OP_MASK \| FLAG_TC))
504	&& pkt->qdcount == htons (1))
505	{
506	char qname[MAXSIZE];
507	int qlen = pkt->decode_label ((char *)qname, MAXSIZE - offs, offs);
508
509	u16 qtype = (pkt) [offs++] << 8; qtype \|= (pkt) [offs++];
510	u16 qclass = (pkt) [offs++] << 8; qclass \|= (pkt) [offs++];
511
512	pkt->qdcount = htons (1);
513	pkt->ancount = 0;
514	pkt->nscount = 0; // should be self, as other nameservers reply like this
515	pkt->arcount = 0; // a record for self, as other nameservers reply like this
516
517	pkt->flags = htons (DEFAULT_SERVER_FLAGS \| FLAG_RCODE_NXDOMAIN);
518
519	int dlen = strlen (THISNODE->domain);
520
521	if (qclass == RR_CLASS_IN
522	&& (qtype == RR_TYPE_ANY \|\| qtype == RR_TYPE_TXT)
523	&& qlen > dlen + 1
524	&& !memcmp (qname + qlen - dlen - 1, THISNODE->domain, dlen))
525	{
526	// correct class, domain: parse
527	u8 data[MAXSIZE];
528	int datalen = dns64::decode (data, qname, qlen - dlen - 1);
529
530	int client = data[0];
531	int seqno = ((data[1] << 8) \| data[2]) & SEQNO_MASK;
532
533	if (0 < client && client <= conns.size ())
534	{
535	connection *c = conns [client - 1];
536
537	for (vector<dns_rcv *>::iterator i = c->dns_rcvpq.begin ();
538	i != c->dns_rcvpq.end ();
539	++i)
540	if ((*i)->seqno == seqno)
541	{
542	// already seen that request, just reply with the original reply
543	dns_rcv r = i;
544
545	offs = r->pkt->len;
546	memcpy (pkt->at (0), r->pkt->at (0), offs);
547	goto duplicate_request;
548	}
549
550	// new packet, queue
551	c->dnsv4_receive_rep (new dns_rcv (seqno, pkt, data + 3, datalen - 3));
552
553	// now generate reply
554	pkt->ancount = htons (1); // one answer RR
555	pkt->flags = htons (DEFAULT_SERVER_FLAGS \| FLAG_RCODE_OK);
556
557	(*pkt) [offs++] = 0xc0;
558	(pkt) [offs++] = 6 2; // same as in query section
559
560	(pkt) [offs++] = RR_TYPE_TXT >> 8; (pkt) [offs++] = RR_TYPE_TXT;
561	(pkt) [offs++] = RR_CLASS_IN >> 8; (pkt) [offs++] = RR_CLASS_IN;
562
563	(pkt) [offs++] = 0; (pkt) [offs++] = 0;
564	(pkt) [offs++] = 0; (pkt) [offs++] = 0; // TTL
565
566	int dlen = MAX_PKT_SIZE - offs - 2;
567
568	// bind doesn't compress well, so reduce further by one label length
569	dlen -= qlen;
570
571	int rdlen_offs = offs += 2;
572
573	while (c->dns_snddq
574	&& !c->dns_snddq->empty ()
575	&& dlen > 1)
576	{
577	int txtlen = dlen <= 255 ? dlen - 1 : 255;
578
579	if (txtlen > c->dns_snddq->size ())
580	txtlen = c->dns_snddq->size ();
581
582	(*pkt)[offs++] = txtlen;
583	memcpy (pkt->at (offs), c->dns_snddq->begin (), txtlen);
584	offs += txtlen;
585	c->dns_snddq->remove (txtlen);
586
587	dlen -= txtlen + 1;
588	}
589
590	// avoid empty TXT rdata
591	if (offs == rdlen_offs)
592	(*pkt)[offs++] = 0;
593
594	int rdlen = offs - rdlen_offs;
595
596	(*pkt) [rdlen_offs - 2] = rdlen >> 8;
597	(*pkt) [rdlen_offs - 1] = rdlen;
598
599	duplicate_request: ;
600	}
601	else
602	pkt->flags = htons (DEFAULT_SERVER_FLAGS \| FLAG_RCODE_FORMERR);
603	}
604	}
605	else
606	offs = pkt->len;
607
608	pkt->len = offs;
609	return pkt;
610	}
611
612	void
613	vpn::dnsv4_client (dns_packet *pkt)
614	{
615	u16 flags = ntohs (pkt->flags);
616	int offs = 6 * 2; // skip header
617
618	pkt->qdcount = ntohs (pkt->qdcount);
619	pkt->ancount = ntohs (pkt->ancount);
620
621	// go through our request list and find the corresponding request
622	for (vector<dns_req *>::iterator i = dns_sndpq.begin ();
623	i != dns_sndpq.end ();
624	++i)
625	if ((*i)->pkt->id == pkt->id)
626	{
627	connection c = (i)->conn;
628	int seqno = (*i)->seqno;
629	u8 data[MAXSIZE], *datap = data;
630
631	delete *i;
632	dns_sndpq.erase (i);
633
634	if (flags & (FLAG_RESPONSE \| FLAG_OP_MASK \| FLAG_TC))
635	{
636	char qname[MAXSIZE];
637
638	while (pkt->qdcount-- && offs < MAXSIZE - 4)
639	{
640	int qlen = pkt->decode_label ((char *)qname, MAXSIZE - offs, offs);
641	offs += 4; // skip qtype, qclass
642	}
643
644	while (pkt->ancount-- && offs < MAXSIZE - 10)
645	{
646	pkt->decode_label ((char *)qname, MAXSIZE - offs, offs);
647
648	u16 qtype = (pkt) [offs++] << 8; qtype \|= (pkt) [offs++];
649	u16 qclass = (pkt) [offs++] << 8; qclass \|= (pkt) [offs++];
650	u32 ttl = (*pkt) [offs++] << 24;
651	ttl \|= (*pkt) [offs++] << 16;
652	ttl \|= (*pkt) [offs++] << 8;
653	ttl \|= (*pkt) [offs++];
654
655	u16 rdlen = (pkt) [offs++] << 8; rdlen \|= (pkt) [offs++];
656
657	if (rdlen <= MAXSIZE - offs)
658	{
659	// decode bytes, finally
660
661	while (rdlen)
662	{
663	int txtlen = (*pkt) [offs++];
664
665	assert (txtlen + offs < MAXSIZE - 1);
666
667	memcpy (datap, pkt->at (offs), txtlen);
668	datap += txtlen; offs += txtlen;
669
670	rdlen -= txtlen + 1;
671	}
672
673	}
674
675	}
676	}
677
678	if (datap != data)
679	printf ("%02x %02x %02x %02x\n",
680	data[0],
681	data[1],
682	data[2],
683	data[3]);
684
685	printf ("recv %d,%d\n", pkt->id, seqno, datap - data);//D
686	c->dnsv4_receive_rep (new dns_rcv (seqno, pkt, data, datap - data));
687
688	break;
689	}
690
691	delete pkt;
692	}
693
694	void
695	vpn::dnsv4_ev (io_watcher &w, short revents)
696	{
697	if (revents & EVENT_READ)
698	{
699	dns_packet *pkt = new dns_packet;
700	struct sockaddr_in sa;
701	socklen_t sa_len = sizeof (sa);
702
703	pkt->len = recvfrom (w.fd, &((pkt)[0]), MAXSIZE, 0, (sockaddr )&sa, &sa_len);
704
705	if (pkt->len > 0)
706	{
707	if (pkt->flags & htons (FLAG_TC))
708	{
709	slog (L_WARN, _("DNS request/response truncated, check protocol settings."));
710	//TODO connection reset
711	}
712
713	if (THISNODE->dns_port)
714	{
715	pkt = dnsv4_server (pkt);
716	sendto (w.fd, &((pkt)[0]), pkt->len, 0, (sockaddr )&sa, sa_len);
717	}
718	else
719	dnsv4_client (pkt);
720	}
721	}
722	}
723
724	bool
725	connection::send_dnsv4_packet (vpn_packet *pkt, const sockinfo &si, int tos)
726	{
727	// never initialized
728	if (!dns_snddq && !dns_rcvdq)
729	{
730	dns_rcvdq = new byte_stream (MAX_BACKLOG * 2);
731	dns_snddq = new byte_stream (MAX_BACKLOG);
732
733	//dns_rcvseq = dns_sndseq = 0;
734
735	dns_si.set (::conf.dns_forw_host, ::conf.dns_forw_port, PROT_DNSv4);
736	}
737
738	if (!dns_snddq->put (pkt))
739	return false;
740
741	// start timer if neccessary
742	if (!THISNODE->dns_port && !dnsv4_tw.active)
743	dnsv4_cb (dnsv4_tw);
744
745	return true;
746	}
747
748	void
749	connection::dnsv4_cb (time_watcher &w)
750	{
751	// check for timeouts and (re)transmit
752	tstamp next = NOW + 60;
753	dns_req *send = 0;
754
755	for (vector<dns_req *>::iterator i = vpn->dns_sndpq.begin ();
756	i != vpn->dns_sndpq.end ();
757	++i)
758	{
759	dns_req r = i;
760
761	if (r->next <= NOW)
762	{
763	if (!send)
764	{
765	send = r;
766
767	if (r->retry)//D
768	printf ("req %d, retry %d\n", r->pkt->id, r->retry);
769	r->retry++;
770	r->next = NOW + r->retry;
771	}
772	}
773
774	if (r->next < next)
775	next = r->next;
776	}
777
778	if (!send
779	&& vpn->dns_sndpq.size () < MAX_OUTSTANDING)
780	{
781	send = new dns_req (this);
782	send->gen_stream_req (dns_sndseq, dns_snddq);
783	vpn->dns_sndpq.push_back (send);
784
785	dns_sndseq = (dns_sndseq + 1) & SEQNO_MASK;
786	}
787
788	tstamp min_next = NOW + (1. / (tstamp)MAX_RATE);
789
790	if (send)
791	{
792	dns_packet *pkt = send->pkt;
793
794	next = min_next;
795
796	sendto (vpn->dnsv4_fd, &((*pkt)[0]), pkt->len, 0, dns_si.sav4 (), dns_si.salenv4 ());
797	}
798	else if (next < min_next)
799	next = min_next;
800
801	w.start (next);
802	}
803
804	#endif
805