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Add NTP packet validity checks

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This commit is contained in:
Brendan McDonnell 2021-05-23 12:24:15 -04:00
parent 296b0b6847
commit 38a7dffd32
1 changed files with 45 additions and 10 deletions
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55
NTPClient.cpp
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@ -81,6 +81,34 @@ void NTPClient::begin(unsigned int port) {
this->_udpSetup = true;
}
// Perform some validity checks on the packet
// https://datatracker.ietf.org/doc/html/rfc4330#section-4
// Check length before calling
static bool isValid(byte const *ntpPacket)
{
unsigned long highWord = word(ntpPacket[16], ntpPacket[17]);
unsigned long lowWord = word(ntpPacket[18], ntpPacket[19]);
unsigned long refTimeInt = highWord << 16 | lowWord;
highWord = word(ntpPacket[20], ntpPacket[21]);
lowWord = word(ntpPacket[22], ntpPacket[23]);
unsigned long refTimeFrac = highWord << 16 | lowWord;
byte leapIndicator = ((ntpPacket[0] & 0b11000000) >> 6);
byte version = ((ntpPacket[0] & 0b00111000) >> 3);
byte mode = ( ntpPacket[0] & 0b00000111 );
byte stratum = ntpPacket[1];
return
(
(leapIndicator != 3) && // LI != UNSYNC
(version >= 4) &&
((mode == 4) || (mode == 5)) && // Mode == server or broadcast
(stratum >= 1) &&
(stratum <= 15) &&
((refTimeInt != 0) || (refTimeFrac != 0))
);
}
bool NTPClient::forceUpdate() {
#ifdef DEBUG_NTPClient
Serial.println("Update from NTP Server");
@ -102,19 +130,26 @@ bool NTPClient::forceUpdate() {
timeout++;
} while (cb == 0);
this->_lastUpdate = millis() - (10 * (timeout + 1)); // Account for delay in reading the time
if ((cb >= NTP_PACKET_SIZE) &&
(this->_udp->read(this->_packetBuffer, NTP_PACKET_SIZE) == NTP_PACKET_SIZE) &&
isValid(this->_packetBuffer))
{
this->_lastUpdate = millis() - (10 * (timeout + 1)); // Account for delay in reading the time
this->_udp->read(this->_packetBuffer, NTP_PACKET_SIZE);
unsigned long highWord = word(this->_packetBuffer[40], this->_packetBuffer[41]);
unsigned long lowWord = word(this->_packetBuffer[42], this->_packetBuffer[43]);
// combine the four bytes (two words) into a long integer
// this is NTP time (seconds since Jan 1 1900):
unsigned long secsSince1900 = highWord << 16 | lowWord;
unsigned long highWord = word(this->_packetBuffer[40], this->_packetBuffer[41]);
unsigned long lowWord = word(this->_packetBuffer[42], this->_packetBuffer[43]);
// combine the four bytes (two words) into a long integer
// this is NTP time (seconds since Jan 1 1900):
unsigned long secsSince1900 = highWord << 16 | lowWord;
this->_currentEpoc = secsSince1900 - SEVENTYYEARS;
this->_currentEpoc = secsSince1900 - SEVENTYYEARS;
return true; // return true after successful update
return true; // return true after successful update
}
else
{
return false;
}
}
bool NTPClient::update() {