Provide additional safety against misuse

plugins/inputs/powerdns_recursor/protocol_commons.go

@@ -40,11 +40,11 @@ func parseResponse(metrics string) map[string]interface{} {
 // depending on the platform the program is being run on.
 // At the time of writing, the Go type `uint` has the same
 // behavior, where its size and endianness are platform
-// dependent. This means that we can do an unsafe cast to
-// grab the data representing the length, and know that in
-// most cases it'll be what we need. In all other cases,
-// we still handle all error cases gracefully, so the plugin
-// will just fail to gather data.
+// dependent. Using the unsafe method below, and the known
+// integer size, we can "recreate" the corresponding C
+// behavior in an effort to maintain compatibility. Of course
+// in cases where one program is compiled for i386 and the
+// other for amd64 (and similar), this method will fail.
 
 const UIntSizeInBytes = strconv.IntSize / 8
 

plugins/inputs/powerdns_recursor/protocol_v1.go

@@ -60,7 +60,7 @@ func (p *PowerdnsRecursor) gatherFromV1Server(address string, acc telegraf.Accum
 	}
 
 	// Read the response data.
-	buf := make([]byte, 16384)
+	buf := make([]byte, 16_384)
 	n, err := conn.Read(buf)
 	if err != nil {
 		return err

plugins/inputs/powerdns_recursor/protocol_v2.go

@@ -14,7 +14,7 @@ import (
 // Unix datagram socket
 // Synchronous request / response, individual datagrams
 // Datagram 1 => status: uint32
-// Datagram 2 => data: byte[] (max 16384 bytes)
+// Datagram 2 => data: byte[] (max 16_384 bytes)
 func (p *PowerdnsRecursor) gatherFromV2Server(address string, acc telegraf.Accumulator) error {
 	randomNumber := rand.Int63()
 	recvSocket := filepath.Join("/", "var", "run", fmt.Sprintf("pdns_recursor_telegraf%d", randomNumber))
@@ -75,7 +75,7 @@ func (p *PowerdnsRecursor) gatherFromV2Server(address string, acc telegraf.Accum
 	}
 
 	// Read the response data.
-	buf := make([]byte, 16384)
+	buf := make([]byte, 16_384)
 	n, err = conn.Read(buf)
 	if err != nil {
 		return err

plugins/inputs/powerdns_recursor/protocol_v3.go

@@ -56,7 +56,15 @@ func (p *PowerdnsRecursor) gatherFromV3Server(address string, acc telegraf.Accum
 		return err
 	}
 	if responseLength == 0 {
-		return fmt.Errorf("received data length was 0")
+		return fmt.Errorf("received data length was '0'")
+	}
+
+	// Don't allow more than 64kb of data to prevent DOS / issues
+	// with architecture mismatch. V2 protocol allowed for up to
+	// 16kb, so 64kb should give us a pretty good margin for anything
+	// that has been added since.
+	if responseLength > 64*1024 {
+		return fmt.Errorf("received data length was '%v', we only allow up to '%v'", responseLength, 64*1024)
 	}
 
 	data := make([]byte, responseLength)