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pcg |
1.1 |
/* |
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vpn_dns.C -- handle the dns tunnel part of the protocol. |
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Copyright (C) 2003-2004 Marc Lehmann <pcg@goof.com> |
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This program is free software; you can redistribute it and/or modify |
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it under the terms of the GNU General Public License as published by |
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the Free Software Foundation; either version 2 of the License, or |
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(at your option) any later version. |
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This program is distributed in the hope that it will be useful, |
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but WITHOUT ANY WARRANTY; without even the implied warranty of |
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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GNU General Public License for more details. |
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You should have received a copy of the GNU General Public License |
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along with this program; if not, write to the Free Software |
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Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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*/ |
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#include "config.h" |
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#if ENABLE_DNS |
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// dns processing is EXTREMELY ugly. For obvious(?) reasons. |
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// it's a hack, use only in emergency situations please. |
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#include <cstring> |
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#include <sys/types.h> |
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#include <sys/socket.h> |
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#include <sys/wait.h> |
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#include <sys/uio.h> |
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#include <errno.h> |
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#include <time.h> |
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#include <unistd.h> |
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#include <fcntl.h> |
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#include <map> |
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#include "netcompat.h" |
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#include "vpn.h" |
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#if ENABLE_HTTP_PROXY |
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# include "conf.h" |
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#endif |
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#define MIN_RETRY 1. |
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#define MAX_RETRY 60. |
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#define SERVER conf.dns_port |
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/* |
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protocol, in shorthand :) |
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pcg |
1.2 |
client -> server <req> ANY? |
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server -> client <req> TXT <rep> |
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pcg |
1.1 |
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pcg |
1.2 |
<req> is dns64-encoded <client-id:12><recv-seqno:10>[<send-seqno:10><data>] |
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<rep> is dns64-encoded <0:12><recv-seqno:10>[<send-seqno:10><data>] |
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if <client-id> is zero, the connection will be configured: |
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<0:12><0:4>client-id:12><default-ttl:8><max-size:16><flags:16> |
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pcg |
1.1 |
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*/ |
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pcg |
1.2 |
#define MAX_LBL_SIZE 63 |
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#define MAX_PKT_SIZE 512 |
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#define RR_TYPE_TXT 16 |
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#define RR_TYPE_ANY 255 |
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#define RR_CLASS_IN 1 |
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// the "_" is not valid but widely accepted (all octets should be supported, but let's be conservative) |
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struct dns64 |
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{ |
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static const char encode_chars[64 + 1]; |
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static s8 decode_chars[256]; |
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static int encode_len (int bytes) { return (bytes * 8 + 5) / 6; } |
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static int decode_len (int bytes) { return (bytes * 6) / 8; } |
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static void encode (char *dst, u8 *src, int len); |
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static void decode (u8 *dst, char *src, int len); |
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dns64 (); |
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} dns64; |
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const char dns64::encode_chars[64 + 1] = "0123456789-abcdefghijklmnopqrstuvwxyz_ABCDEFGHIJKLMNOPQRSTUVWXYZ"; |
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s8 dns64::decode_chars[256]; |
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dns64::dns64 () |
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{ |
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for (int i = 0; i < 64; i++) |
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decode_chars [encode_chars [i]] = i + 1; |
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} |
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void dns64::encode (char *dst, u8 *src, int len) |
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{ |
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// slow, but easy to debug |
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unsigned int accum, bits = 0; |
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while (len--) |
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{ |
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accum <<= 8; |
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accum |= *src++; |
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bits += 8; |
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while (bits >= 6) |
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{ |
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*dst++ = encode_chars [(accum >> (bits - 6)) & 63]; |
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bits -= 6; |
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} |
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} |
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if (bits) |
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*dst++ = encode_chars [(accum << (6 - bits)) & 63]; |
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} |
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void dns64::decode (u8 *dst, char *src, int len) |
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{ |
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// slow, but easy to debug |
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unsigned int accum, bits = 0; |
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while (len--) |
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{ |
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s8 chr = decode_chars [(u8)*src++]; |
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if (!chr) |
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break; |
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accum <<= 6; |
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accum |= chr - 1; |
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bits += 6; |
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while (bits >= 8) |
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{ |
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*dst++ = accum >> (bits - 8); |
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bits -= 8; |
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} |
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} |
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} |
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#define FLAG_QUERY ( 0 << 15) |
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#define FLAG_RESPONSE ( 1 << 15) |
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#define FLAG_OP_MASK (15 << 14) |
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#define FLAG_OP_QUERY ( 0 << 11) |
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#define FLAG_AA ( 1 << 10) |
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#define FLAG_TC ( 1 << 9) |
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#define FLAG_RD ( 1 << 8) |
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#define FLAG_RA ( 1 << 7) |
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#define FLAG_RCODE_MASK (15 << 0) |
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#define FLAG_RCODE_OK ( 0 << 0) |
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#define FLAG_RCODE_FORMERR ( 1 << 0) |
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#define FLAG_RCODE_SERVFAIL ( 2 << 0) |
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#define FLAG_RCODE_NXDOMAIN ( 3 << 0) |
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#define FLAG_RCODE_REFUSED ( 5 << 0) |
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#define DEFAULT_CLIENT_FLAGS (FLAG_QUERY | FLAG_OP_QUERY | FLAG_RD) |
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#define DEFAULT_SERVER_FLAGS (FLAG_RESPONSE | FLAG_OP_QUERY | FLAG_AA | FLAG_RD) |
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struct dns_packet : net_packet |
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{ |
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u16 id; |
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u16 flags; // QR:1 Opcode:4 AA:1 TC:1 RD:1 RA:1 Z:3 RCODE:4 |
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u16 qdcount, ancount, nscount, arcount; |
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u8 data[MAXSIZE - 6 * 2]; |
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int decode_label (char *data, int size, int &offs); |
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}; |
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int dns_packet::decode_label (char *data, int size, int &offs) |
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{ |
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char *orig = data; |
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memset (data, 0, size); |
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while (offs < size - 1) |
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{ |
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u8 len = (*this)[offs++]; |
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if (!len) |
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break; |
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else if (len < 64) |
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{ |
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if (size < len + 1 || offs + len >= MAXSIZE - 1) |
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break; |
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memcpy (data, &((*this)[offs]), len); |
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data += len; size -= len; offs += len; |
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*data++ = '.'; size--; |
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} |
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else |
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{ |
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int offs2 = ((len & 63) << 8) + (*this)[offs++]; |
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data += decode_label (data, size, offs2); |
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break; |
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} |
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} |
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return data - orig; |
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} |
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struct dns_cfg |
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{ |
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u8 id1, id2, id3; |
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u8 def_ttl; |
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u8 unused1; |
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u16 max_size; |
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u8 flags1, flags2; |
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}; |
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// reply to client-poll |
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void dnsv4_poll (dns_packet *pkt, int &offs) |
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{ |
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int dlen = MAX_PKT_SIZE - offs - 2; |
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(*pkt) [offs++] = 0; |
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(*pkt) [offs++] = 5; |
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memcpy (&((*pkt)[offs]), "\01H\02\xff\x00", 5); |
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offs += 5; |
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pkt->ancount = htons (1); |
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pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_OK); |
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printf ("we have room for %d bytes\n", dlen); |
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} |
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pcg |
1.1 |
void |
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vpn::dnsv4_ev (io_watcher &w, short revents) |
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{ |
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if (revents & EVENT_READ) |
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{ |
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pcg |
1.2 |
dns_packet *pkt = new dns_packet; |
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pcg |
1.1 |
struct sockaddr_in sa; |
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socklen_t sa_len = sizeof (sa); |
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pcg |
1.2 |
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int len = recvfrom (w.fd, &((*pkt)[0]), MAXSIZE, 0, (sockaddr *)&sa, &sa_len); |
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pkt->len = len; |
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u16 flags = ntohs (pkt->flags); |
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if (THISNODE->dns_port) |
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{ |
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// server |
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pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_FORMERR); |
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int offs = 6 * 2; // skip header |
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if (!(flags & (FLAG_RESPONSE | FLAG_OP_MASK | FLAG_TC)) |
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&& pkt->qdcount == htons (1)) |
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{ |
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char qname[MAXSIZE]; |
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int qlen = pkt->decode_label ((char *)qname, MAXSIZE, offs); |
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printf ("rcvd packet len %d, id%04x flags%04x q%04x a%04x n%04x a%04x <%s>\n", len, |
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pkt->id, flags, pkt->qdcount, pkt->ancount, pkt->nscount, pkt->arcount, qname);//D |
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u16 qtype = (*pkt) [offs++] << 8; qtype |= (*pkt) [offs++]; |
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u16 qclass = (*pkt) [offs++] << 8; qclass |= (*pkt) [offs++]; |
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pkt->qdcount = htons (1); |
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pkt->ancount = 0; |
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pkt->nscount = 0; // should be self, as other nameservers reply like this |
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pkt->arcount = 0; // a record for self, as other nameservers reply like this |
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pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_NXDOMAIN); |
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int dlen = strlen (THISNODE->domain); |
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if (qclass == RR_CLASS_IN |
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&& (qtype == RR_TYPE_ANY || qtype == RR_TYPE_TXT) |
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&& qlen > dlen + 1 |
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&& !memcmp (qname + qlen - dlen - 1, THISNODE->domain, dlen)) |
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{ |
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// correct class, now generate reply |
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pkt->ancount = htons (1); // one answer RR |
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(*pkt) [offs++] = 0xc0; |
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(*pkt) [offs++] = 6 * 2; // same as in query section |
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(*pkt) [offs++] = RR_TYPE_TXT >> 8; (*pkt) [offs++] = RR_TYPE_TXT; |
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(*pkt) [offs++] = RR_CLASS_IN >> 8; (*pkt) [offs++] = RR_CLASS_IN; |
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(*pkt) [offs++] = 0; (*pkt) [offs++] = 0; |
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(*pkt) [offs++] = 0; (*pkt) [offs++] = 0; // TTL |
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dnsv4_poll (pkt, offs); |
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printf ("correct class\n"); |
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} |
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} |
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sendto (w.fd, &((*pkt)[0]), offs, 0, (sockaddr *)&sa, sa_len); |
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} |
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else |
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{ |
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// client |
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} |
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pcg |
1.1 |
} |
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} |
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bool |
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vpn::send_dnsv4_packet (vpn_packet *pkt, const sockinfo &si, int tos) |
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{ |
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//return i->send_packet (pkt, tos); |
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} |
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#endif |
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