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Optimize MDNS to prevent overflow and endless loop (esp8266#2333)
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* Optimize MDNS to prevent overflow and endless loop

* Handle better non-esp services

* leave debug off

* better name resolution for external devices

* strip name length (did not show in IDE)
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@me-no-dev @igrr
me-no-dev authored and igrr committed Aug 1, 2016
1 parent db5e20f commit c4c207a
Showing 1 changed file with 48 additions and 14 deletions.
62 changes: 48 additions & 14 deletions libraries/ESP8266mDNS/ESP8266mDNS.cpp
View file
Expand Up @@ -493,11 +493,11 @@ void MDNSResponder::_parsePacket(){
return;
}

int numAnswers = packetHeader[3];
int numAnswers = packetHeader[3] + packetHeader[5];
// Assume that the PTR answer always comes first and that it is always accompanied by a TXT, SRV, AAAA (optional) and A answer in the same packet.
if (numAnswers < 4) {
#ifdef MDNS_DEBUG_RX
Serial.println("Expected a packet with 4 answers, returning");
Serial.printf("Expected a packet with 4 or more answers, got %u\n", numAnswers);
#endif
_conn->flush();
return;
Expand All @@ -510,11 +510,14 @@ void MDNSResponder::_parsePacket(){
bool serviceMatch = false;
MDNSAnswer *answer;
uint8_t partsCollected = 0;
uint8_t stringsRead = 0;

answerHostName[0] = '\0';

// Clear answer list
if (_newQuery) {
int numAnswers = _getNumAnswers();
for (int n = numAnswers - 1; n >= 0; n--) {
int oldAnswers = _getNumAnswers();
for (int n = oldAnswers - 1; n >= 0; n--) {
answer = _getAnswerFromIdx(n);
os_free(answer->hostname);
os_free(answer);
Expand All @@ -526,21 +529,29 @@ void MDNSResponder::_parsePacket(){

while (numAnswers--) {
// Read name
stringsRead = 0;
do {
tmp8 = _conn_read8();
if (tmp8 & 0xC0) { // Compressed pointer (not supported)
tmp8 = _conn_read8();
break;
}
if (tmp8 == 0x00) { // Énd of name
if (tmp8 == 0x00) { // End of name
break;
}
if(stringsRead > 3){
#ifdef MDNS_DEBUG_RX
Serial.println("failed to read the response name");
#endif
_conn->flush();
return;
}
_conn_readS(serviceName, tmp8);
serviceName[tmp8] = '\0';
#ifdef MDNS_DEBUG_RX
Serial.printf(" %d ", tmp8);
for (int n = 0; n < tmp8; n++) {
Serial.printf("%02x ", serviceName[n]);
Serial.printf("%c", serviceName[n]);
}
Serial.println();
#endif
Expand All @@ -552,23 +563,41 @@ void MDNSResponder::_parsePacket(){
#endif
}
}
stringsRead++;
} while (true);

uint16_t answerType = _conn_read16(); // Read type
uint16_t answerClass = _conn_read16(); // Read class
uint32_t answerTtl = _conn_read32(); // Read ttl
uint16_t answerRdlength = _conn_read16(); // Read rdlength

if(answerRdlength > 255){
if(answerType == MDNS_TYPE_TXT && answerRdlength < 1460){
while(--answerRdlength) _conn->read();
} else {
#ifdef MDNS_DEBUG_RX
Serial.printf("Data len too long! %u\n", answerRdlength);
#endif
_conn->flush();
return;
}
}

#ifdef MDNS_DEBUG_RX
Serial.printf("type: %04x rdlength: %d\n", answerType, answerRdlength);
#endif

if (answerType == MDNS_TYPE_PTR) {
partsCollected |= 0x01;
_conn_readS(hostName, answerRdlength); // Read rdata
if(hostName[answerRdlength-2] & 0xc0){
memcpy(answerHostName, hostName+1, answerRdlength-3);
answerHostName[answerRdlength-3] = '\0';
}
#ifdef MDNS_DEBUG_RX
Serial.printf("PTR %d ", answerRdlength);
for (int n = 0; n < answerRdlength; n++) {
Serial.printf("%02x ", hostName[n]);
Serial.printf("%c", hostName[n]);
}
Serial.println();
#endif
Expand All @@ -578,8 +607,9 @@ void MDNSResponder::_parsePacket(){
partsCollected |= 0x02;
_conn_readS(hostName, answerRdlength); // Read rdata
#ifdef MDNS_DEBUG_RX
Serial.printf("TXT %d ", answerRdlength);
for (int n = 0; n < answerRdlength; n++) {
Serial.printf("%02x ", hostName[n]);
Serial.printf("%c", hostName[n]);
}
Serial.println();
#endif
Expand All @@ -594,14 +624,16 @@ void MDNSResponder::_parsePacket(){
// Read hostname
tmp8 = _conn_read8();
if (tmp8 & 0xC0) { // Compressed pointer (not supported)
#ifdef MDNS_DEBUG_RX
Serial.println("Skipping compressed pointer");
#endif
tmp8 = _conn_read8();
}
else {
_conn_readS(answerHostName, tmp8);
answerHostName[tmp8] = '\0';
#ifdef MDNS_DEBUG_RX
Serial.printf(" %d ", tmp8);
Serial.printf("SRV %d ", tmp8);
for (int n = 0; n < tmp8; n++) {
Serial.printf("%02x ", answerHostName[n]);
}
Expand All @@ -621,7 +653,7 @@ void MDNSResponder::_parsePacket(){
}
else {
#ifdef MDNS_DEBUG_RX
Serial.printf("Ignoring unsupported type %d\n", tmp8);
Serial.printf("Ignoring unsupported type %02x\n", tmp8);
#endif
for (int n = 0; n < answerRdlength; n++)
(void)_conn_read8();
Expand Down Expand Up @@ -654,6 +686,8 @@ void MDNSResponder::_parsePacket(){
}
answer->hostname = (char *)os_malloc(strlen(answerHostName) + 1);
os_strcpy(answer->hostname, answerHostName);
_conn->flush();
return;
}
}

Expand All @@ -663,7 +697,7 @@ void MDNSResponder::_parsePacket(){

// PARSE REQUEST NAME

hostNameLen = _conn_read8();
hostNameLen = _conn_read8() % 255;
_conn_readS(hostName, hostNameLen);
hostName[hostNameLen] = '\0';

Expand All @@ -685,7 +719,7 @@ void MDNSResponder::_parsePacket(){
}

if(!serviceParsed){
serviceNameLen = _conn_read8();
serviceNameLen = _conn_read8() % 255;
_conn_readS(serviceName, serviceNameLen);
serviceName[serviceNameLen] = '\0';

Expand Down Expand Up @@ -718,7 +752,7 @@ void MDNSResponder::_parsePacket(){
}

if(!protoParsed){
protoNameLen = _conn_read8();
protoNameLen = _conn_read8() % 255;
_conn_readS(protoName, protoNameLen);
protoName[protoNameLen] = '\0';
if(protoNameLen == 4 && protoName[0] == '_'){
Expand All @@ -740,7 +774,7 @@ void MDNSResponder::_parsePacket(){

if(!localParsed){
char localName[32];
uint8_t localNameLen = _conn_read8();
uint8_t localNameLen = _conn_read8() % 31;
_conn_readS(localName, localNameLen);
localName[localNameLen] = '\0';
tmp = _conn_read8();
Expand Down

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