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Compressed dns (#3769)

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* Add UdpContext seek and tell

* Add support for DNS compressed messages

* mDNS compressed pointer: Validate offset before jumping
This commit is contained in:
Jonatan Olofsson
2018-03-16 13:46:35 +01:00
committed by Develo
parent 836c7da8cc
commit 461c922586
3 changed files with 89 additions and 21 deletions
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88
libraries/ESP8266mDNS/ESP8266mDNS.cpp
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@ -542,15 +542,33 @@ void MDNSResponder::_parsePacket(){
while (numAnswers--) {
// Read name
stringsRead = 0;
size_t last_bufferpos = 0;
do {
tmp8 = _conn_read8();
if (tmp8 & 0xC0) { // Compressed pointer (not supported)
tmp8 = _conn_read8();
break;
}
if (tmp8 == 0x00) { // End of name
break;
}
if (tmp8 & 0xC0) { // Compressed pointer
uint16_t offset = ((((uint16_t)tmp8) & ~0xC0) << 8) | _conn_read8();
if (_conn->isValidOffset(offset)) {
last_bufferpos = _conn->tell();
#ifdef DEBUG_ESP_MDNS_RX
DEBUG_ESP_PORT.print("Compressed pointer, jumping from ");
DEBUG_ESP_PORT.print(last_bufferpos);
DEBUG_ESP_PORT.print(" to ");
DEBUG_ESP_PORT.println(offset);
#endif
_conn->seek(offset);
tmp8 = _conn_read8();
}
else {
#ifdef DEBUG_ESP_MDNS_RX
DEBUG_ESP_PORT.print("Skipping malformed compressed pointer");
#endif
tmp8 = _conn_read8();
break;
}
}
if(stringsRead > 3){
#ifdef DEBUG_ESP_MDNS_RX
DEBUG_ESP_PORT.println("failed to read the response name");
@ -577,6 +595,14 @@ void MDNSResponder::_parsePacket(){
}
stringsRead++;
} while (true);
if (last_bufferpos > 0)
{
_conn->seek(last_bufferpos);
#ifdef DEBUG_ESP_MDNS_RX
DEBUG_ESP_PORT.print("Compressed pointer, jumping back to ");
DEBUG_ESP_PORT.println(last_bufferpos);
#endif
}
uint16_t answerType = _conn_read16(); // Read type
uint16_t answerClass = _conn_read16(); // Read class
@ -635,32 +661,54 @@ void MDNSResponder::_parsePacket(){
uint16_t answerPrio = _conn_read16(); // Read priority
uint16_t answerWeight = _conn_read16(); // Read weight
answerPort = _conn_read16(); // Read port
last_bufferpos = 0;
(void) answerPrio;
(void) answerWeight;
// Read hostname
tmp8 = _conn_read8();
if (tmp8 & 0xC0) { // Compressed pointer (not supported)
if (tmp8 & 0xC0) { // Compressed pointer
uint16_t offset = ((((uint16_t)tmp8) & ~0xC0) << 8) | _conn_read8();
if (_conn->isValidOffset(offset)) {
last_bufferpos = _conn->tell();
#ifdef DEBUG_ESP_MDNS_RX
DEBUG_ESP_PORT.println("Skipping compressed pointer");
DEBUG_ESP_PORT.print("Compressed pointer, jumping from ");
DEBUG_ESP_PORT.print(last_bufferpos);
DEBUG_ESP_PORT.print(" to ");
DEBUG_ESP_PORT.println(offset);
#endif
tmp8 = _conn_read8();
_conn->seek(offset);
tmp8 = _conn_read8();
}
else {
#ifdef DEBUG_ESP_MDNS_RX
DEBUG_ESP_PORT.print("Skipping malformed compressed pointer");
#endif
tmp8 = _conn_read8();
break;
}
}
else {
_conn_readS(answerHostName, tmp8);
answerHostName[tmp8] = '\0';
_conn_readS(answerHostName, tmp8);
answerHostName[tmp8] = '\0';
#ifdef DEBUG_ESP_MDNS_RX
DEBUG_ESP_PORT.printf("SRV %d ", tmp8);
for (int n = 0; n < tmp8; n++) {
DEBUG_ESP_PORT.printf("%02x ", answerHostName[n]);
}
DEBUG_ESP_PORT.printf("\n%s\n", answerHostName);
DEBUG_ESP_PORT.printf("SRV %d ", tmp8);
for (int n = 0; n < tmp8; n++) {
DEBUG_ESP_PORT.printf("%02x ", answerHostName[n]);
}
DEBUG_ESP_PORT.printf("\n%s\n", answerHostName);
#endif
if (answerRdlength - (6 + 1 + tmp8) > 0) { // Skip any remaining rdata
_conn_readS(hostName, answerRdlength - (6 + 1 + tmp8));
}
if (last_bufferpos > 0)
{
_conn->seek(last_bufferpos);
tmp8 = 2; // Size of compression octets
#ifdef DEBUG_ESP_MDNS_RX
DEBUG_ESP_PORT.print("Compressed pointer, jumping back to ");
DEBUG_ESP_PORT.println(last_bufferpos);
#endif
}
if (answerRdlength - (6 + 1 + tmp8) > 0) { // Skip any remaining rdata
_conn_readS(hostName, answerRdlength - (6 + 1 + tmp8));
}
}
@ -675,7 +723,7 @@ void MDNSResponder::_parsePacket(){
DEBUG_ESP_PORT.printf("Ignoring unsupported type %02x\n", tmp8);
#endif
for (int n = 0; n < answerRdlength; n++)
(void)_conn_read8();
(void)_conn_read8();
}
if ((partsCollected == 0x0F) && serviceMatch) {