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52 | |
52 | |
53 | /* |
53 | /* |
54 | |
54 | |
55 | protocol, in shorthand :) |
55 | protocol, in shorthand :) |
56 | |
56 | |
57 | <cseqno> ANY? poll for more data |
57 | client -> server <req> ANY? |
58 | => TXT <sseqno><data> |
58 | server -> client <req> TXT <rep> |
59 | <cseqno><data> TXT? send more data |
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60 | => TXT <empty> |
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61 | |
59 | |
62 | sequence numbers are 12 bit, 9 bit packet-number and 3 bit fragment id (7 |
60 | <req> is dns64-encoded <client-id:12><recv-seqno:10>[<send-seqno:10><data>] |
63 | - id, actually) last fragment is sent first, however |
61 | <rep> is dns64-encoded <0:12><recv-seqno:10>[<send-seqno:10><data>] |
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62 | |
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63 | if <client-id> is zero, the connection will be configured: |
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64 | |
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65 | <0:12><0:4>client-id:12><default-ttl:8><max-size:16><flags:16> |
64 | |
66 | |
65 | */ |
67 | */ |
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68 | |
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69 | #define MAX_LBL_SIZE 63 |
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70 | #define MAX_PKT_SIZE 512 |
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71 | |
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72 | #define RR_TYPE_TXT 16 |
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73 | #define RR_TYPE_ANY 255 |
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74 | #define RR_CLASS_IN 1 |
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75 | |
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76 | // the "_" is not valid but widely accepted (all octets should be supported, but let's be conservative) |
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77 | struct dns64 |
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78 | { |
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79 | static const char encode_chars[64 + 1]; |
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80 | static s8 decode_chars[256]; |
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81 | |
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82 | static int encode_len (int bytes) { return (bytes * 8 + 5) / 6; } |
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83 | static int decode_len (int bytes) { return (bytes * 6) / 8; } |
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84 | static void encode (char *dst, u8 *src, int len); |
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85 | static void decode (u8 *dst, char *src, int len); |
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86 | |
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87 | dns64 (); |
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88 | } dns64; |
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89 | |
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90 | const char dns64::encode_chars[64 + 1] = "0123456789-abcdefghijklmnopqrstuvwxyz_ABCDEFGHIJKLMNOPQRSTUVWXYZ"; |
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91 | s8 dns64::decode_chars[256]; |
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92 | |
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93 | dns64::dns64 () |
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94 | { |
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95 | for (int i = 0; i < 64; i++) |
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96 | decode_chars [encode_chars [i]] = i + 1; |
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97 | } |
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98 | |
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99 | void dns64::encode (char *dst, u8 *src, int len) |
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100 | { |
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101 | // slow, but easy to debug |
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102 | unsigned int accum, bits = 0; |
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103 | |
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104 | while (len--) |
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105 | { |
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106 | accum <<= 8; |
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107 | accum |= *src++; |
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108 | bits += 8; |
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109 | |
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110 | while (bits >= 6) |
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111 | { |
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112 | *dst++ = encode_chars [(accum >> (bits - 6)) & 63]; |
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113 | bits -= 6; |
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114 | } |
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115 | } |
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116 | |
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117 | if (bits) |
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118 | *dst++ = encode_chars [(accum << (6 - bits)) & 63]; |
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119 | } |
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120 | |
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121 | void dns64::decode (u8 *dst, char *src, int len) |
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122 | { |
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123 | // slow, but easy to debug |
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124 | unsigned int accum, bits = 0; |
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125 | |
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126 | while (len--) |
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127 | { |
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128 | s8 chr = decode_chars [(u8)*src++]; |
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129 | |
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130 | |
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131 | if (!chr) |
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132 | break; |
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133 | |
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134 | accum <<= 6; |
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135 | accum |= chr - 1; |
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136 | bits += 6; |
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137 | |
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138 | while (bits >= 8) |
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139 | { |
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140 | *dst++ = accum >> (bits - 8); |
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141 | bits -= 8; |
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142 | } |
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143 | } |
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144 | } |
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145 | |
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146 | #define FLAG_QUERY ( 0 << 15) |
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147 | #define FLAG_RESPONSE ( 1 << 15) |
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148 | #define FLAG_OP_MASK (15 << 14) |
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149 | #define FLAG_OP_QUERY ( 0 << 11) |
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150 | #define FLAG_AA ( 1 << 10) |
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151 | #define FLAG_TC ( 1 << 9) |
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152 | #define FLAG_RD ( 1 << 8) |
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153 | #define FLAG_RA ( 1 << 7) |
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154 | #define FLAG_RCODE_MASK (15 << 0) |
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155 | #define FLAG_RCODE_OK ( 0 << 0) |
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156 | #define FLAG_RCODE_FORMERR ( 1 << 0) |
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157 | #define FLAG_RCODE_SERVFAIL ( 2 << 0) |
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158 | #define FLAG_RCODE_NXDOMAIN ( 3 << 0) |
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159 | #define FLAG_RCODE_REFUSED ( 5 << 0) |
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160 | |
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161 | #define DEFAULT_CLIENT_FLAGS (FLAG_QUERY | FLAG_OP_QUERY | FLAG_RD) |
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162 | #define DEFAULT_SERVER_FLAGS (FLAG_RESPONSE | FLAG_OP_QUERY | FLAG_AA | FLAG_RD) |
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163 | |
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164 | struct dns_packet : net_packet |
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165 | { |
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166 | u16 id; |
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167 | u16 flags; // QR:1 Opcode:4 AA:1 TC:1 RD:1 RA:1 Z:3 RCODE:4 |
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168 | u16 qdcount, ancount, nscount, arcount; |
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169 | |
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170 | u8 data[MAXSIZE - 6 * 2]; |
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171 | |
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172 | int decode_label (char *data, int size, int &offs); |
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173 | }; |
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174 | |
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175 | int dns_packet::decode_label (char *data, int size, int &offs) |
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176 | { |
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177 | char *orig = data; |
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178 | |
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179 | memset (data, 0, size); |
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180 | |
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181 | while (offs < size - 1) |
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182 | { |
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183 | u8 len = (*this)[offs++]; |
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184 | |
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185 | if (!len) |
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186 | break; |
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187 | else if (len < 64) |
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188 | { |
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189 | if (size < len + 1 || offs + len >= MAXSIZE - 1) |
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190 | break; |
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191 | |
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192 | memcpy (data, &((*this)[offs]), len); |
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193 | |
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194 | data += len; size -= len; offs += len; |
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195 | *data++ = '.'; size--; |
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196 | } |
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197 | else |
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198 | { |
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199 | int offs2 = ((len & 63) << 8) + (*this)[offs++]; |
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200 | |
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201 | data += decode_label (data, size, offs2); |
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202 | break; |
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203 | } |
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204 | } |
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205 | |
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206 | return data - orig; |
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207 | } |
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208 | |
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209 | struct dns_cfg |
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210 | { |
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211 | u8 id1, id2, id3; |
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212 | u8 def_ttl; |
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213 | u8 unused1; |
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214 | u16 max_size; |
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215 | u8 flags1, flags2; |
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216 | }; |
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217 | |
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218 | // reply to client-poll |
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219 | void dnsv4_poll (dns_packet *pkt, int &offs) |
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220 | { |
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221 | int dlen = MAX_PKT_SIZE - offs - 2; |
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222 | |
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223 | (*pkt) [offs++] = 0; |
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224 | (*pkt) [offs++] = 5; |
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225 | memcpy (&((*pkt)[offs]), "\01H\02\xff\x00", 5); |
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226 | offs += 5; |
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227 | |
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228 | pkt->ancount = htons (1); |
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229 | pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_OK); |
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230 | |
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231 | printf ("we have room for %d bytes\n", dlen); |
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232 | } |
66 | |
233 | |
67 | void |
234 | void |
68 | vpn::dnsv4_ev (io_watcher &w, short revents) |
235 | vpn::dnsv4_ev (io_watcher &w, short revents) |
69 | { |
236 | { |
70 | if (revents & EVENT_READ) |
237 | if (revents & EVENT_READ) |
71 | { |
238 | { |
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239 | dns_packet *pkt = new dns_packet; |
72 | struct sockaddr_in sa; |
240 | struct sockaddr_in sa; |
73 | socklen_t sa_len = sizeof (sa); |
241 | socklen_t sa_len = sizeof (sa); |
74 | int len; |
242 | |
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243 | int len = recvfrom (w.fd, &((*pkt)[0]), MAXSIZE, 0, (sockaddr *)&sa, &sa_len); |
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244 | pkt->len = len; |
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245 | |
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246 | u16 flags = ntohs (pkt->flags); |
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247 | |
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248 | if (THISNODE->dns_port) |
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249 | { |
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250 | // server |
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251 | pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_FORMERR); |
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252 | |
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253 | int offs = 6 * 2; // skip header |
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254 | |
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255 | if (!(flags & (FLAG_RESPONSE | FLAG_OP_MASK | FLAG_TC)) |
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256 | && pkt->qdcount == htons (1)) |
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257 | { |
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258 | char qname[MAXSIZE]; |
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259 | int qlen = pkt->decode_label ((char *)qname, MAXSIZE, offs); |
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260 | |
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261 | printf ("rcvd packet len %d, id%04x flags%04x q%04x a%04x n%04x a%04x <%s>\n", len, |
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262 | pkt->id, flags, pkt->qdcount, pkt->ancount, pkt->nscount, pkt->arcount, qname);//D |
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263 | |
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264 | u16 qtype = (*pkt) [offs++] << 8; qtype |= (*pkt) [offs++]; |
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265 | u16 qclass = (*pkt) [offs++] << 8; qclass |= (*pkt) [offs++]; |
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266 | |
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267 | pkt->qdcount = htons (1); |
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268 | pkt->ancount = 0; |
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269 | pkt->nscount = 0; // should be self, as other nameservers reply like this |
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270 | pkt->arcount = 0; // a record for self, as other nameservers reply like this |
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271 | |
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272 | pkt->flags = htons (DEFAULT_SERVER_FLAGS | FLAG_RCODE_NXDOMAIN); |
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273 | |
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274 | int dlen = strlen (THISNODE->domain); |
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275 | |
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276 | if (qclass == RR_CLASS_IN |
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277 | && (qtype == RR_TYPE_ANY || qtype == RR_TYPE_TXT) |
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278 | && qlen > dlen + 1 |
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279 | && !memcmp (qname + qlen - dlen - 1, THISNODE->domain, dlen)) |
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280 | { |
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281 | // correct class, now generate reply |
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282 | pkt->ancount = htons (1); // one answer RR |
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283 | |
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284 | (*pkt) [offs++] = 0xc0; |
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285 | (*pkt) [offs++] = 6 * 2; // same as in query section |
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286 | |
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287 | (*pkt) [offs++] = RR_TYPE_TXT >> 8; (*pkt) [offs++] = RR_TYPE_TXT; |
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288 | (*pkt) [offs++] = RR_CLASS_IN >> 8; (*pkt) [offs++] = RR_CLASS_IN; |
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289 | |
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290 | (*pkt) [offs++] = 0; (*pkt) [offs++] = 0; |
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291 | (*pkt) [offs++] = 0; (*pkt) [offs++] = 0; // TTL |
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292 | |
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293 | dnsv4_poll (pkt, offs); |
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294 | printf ("correct class\n"); |
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295 | } |
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296 | } |
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297 | |
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298 | sendto (w.fd, &((*pkt)[0]), offs, 0, (sockaddr *)&sa, sa_len); |
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299 | } |
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300 | else |
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301 | { |
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302 | // client |
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303 | } |
75 | } |
304 | } |
76 | } |
305 | } |
77 | |
306 | |
78 | bool |
307 | bool |
79 | vpn::send_dnsv4_packet (vpn_packet *pkt, const sockinfo &si, int tos) |
308 | vpn::send_dnsv4_packet (vpn_packet *pkt, const sockinfo &si, int tos) |