From 471a80638df4bb6370db35609c82d0fa901598ce Mon Sep 17 00:00:00 2001
From: AJ ONeal <aj@daplie.com>
Date: Mon, 9 Oct 2017 13:48:54 -0600
Subject: [PATCH] note if data is truncated

---
 bin/debug.js         | 12 ++++++++++--
 dns.unpack-labels.js |  5 +++++
 parser/type.ns.js    | 15 ++++++++++-----
 parser/type.ptr.js   | 12 ++++++++----
 4 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/bin/debug.js b/bin/debug.js
index 4fee566..0bbde9e 100644
--- a/bin/debug.js
+++ b/bin/debug.js
@@ -65,6 +65,11 @@ function unpackQuestionLabels(opts) {
 
   while (true) {
     if (total >= len) {
+      opts.trunc = true;
+      console.warn('');
+      console.warn('[WARNING] The label was truncated by byte length of message or rdata.');
+      console.warn('[WARNING] Depending on the Resource Record type, that may be a parse error.');
+      console.warn('');
       break;
     }
     labelLen = dv.getUint8(total, false); // additional count
@@ -72,8 +77,11 @@ function unpackQuestionLabels(opts) {
     if (!labelLen) {
       break;
     }
-    if (192 === labelLen) {
-      var pointer = dv.getUint8(total, false);
+    if (labelLen >= 0xc0) {
+      // (11 000000 & whatever) signifies pointer
+      // (00 111111 & whatever) bitmask for potentially large pointer
+      // (00 000001   11111111) largest realistic pointer value (512 byte message size)
+      var pointer = ((labelLen & 0x3f) << 8) | dv.getUint8(total, false);
       console.log('Found a pointer to'
         + ' 0x' + pointer.toString(16) + ' (' + pointer + ')'
         + ' at byte index'
diff --git a/dns.unpack-labels.js b/dns.unpack-labels.js
index 9a82d43..46ac18f 100644
--- a/dns.unpack-labels.js
+++ b/dns.unpack-labels.js
@@ -26,11 +26,16 @@ exports.DNS_UNPACK_LABELS = function (ui8, ptr, q) {
     len = ui8[total];
     if (len === undefined){
       // RDATA is terminated by undefined, not len === 0
+      q.trunc = true;
       break;
     }
 
     // Handle message compression pointers. See 4.1.4 of RFC1035 for details.
+    // 0xc0 // 192 // parseInt('11000000', 2).toString(16)
     if (len >= 0xc0) {
+      // Only the two highest bits are used to signify the pointer.
+      // The remaining bits may be used to specify the address of the pointer
+      // (it would seem that only 1 extra bit is actually used since the message size is 512 bytes)
       var cpptr = ((ui8[total] & 0x3f) << 8) |  ui8[total + 1];
 
       // We're not coming back, so if this is the first time we're following one of
diff --git a/parser/type.ns.js b/parser/type.ns.js
index e03d102..20b9a28 100644
--- a/parser/type.ns.js
+++ b/parser/type.ns.js
@@ -1,6 +1,10 @@
 (function (exports) {
 'use strict';
 
+// FORMAT:
+// name   ttl   class   rr     name
+// foo.   15    IN      NS     www.example.com.
+
 // Comes in variable lengths. It is the name of the primary Master for the Domain.
 // For example 'ns1.example.com'
 // It may be a label, pointer or any combination
@@ -8,11 +12,12 @@ var unpackLabels = exports.DNS_UNPACK_LABELS || require('../dns.unpack-labels.js
 
 
 exports.DNS_PARSER_TYPE_NS = function (ab , packet, record) {
-    record.data = unpackLabels(new Uint8Array(ab), record.rdstart, { byteLength: 0, cpcount: 0, labels: [], name: '' }).name;
-    return record;
-
+  var labelInfo = unpackLabels(new Uint8Array(ab), record.rdstart, { byteLength: 0, cpcount: 0, labels: [], name: '' });
+  if (record.trunc) {
+    throw new Error("RDATA type NS must be `null`-terminated, not truncated by rdata length.");
+  }
+  record.data = labelInfo.name;
+  return record;
 };
 
 }('undefined' !== typeof window ? window : exports));
-
-
diff --git a/parser/type.ptr.js b/parser/type.ptr.js
index 1e6e068..83de4a2 100644
--- a/parser/type.ptr.js
+++ b/parser/type.ptr.js
@@ -6,12 +6,16 @@
 // to a host name.
 
 // FORMAT:
-// ame ttl  class   rr     name
-// 15         IN     PTR    www.example.com.
+// name   ttl   class   rr     name
+// foo.   15    IN      PTR    www.example.com.
 
 var unpackLabels = exports.DNS_UNPACK_LABELS || require('../dns.unpack-labels.js').DNS_UNPACK_LABELS;
 exports.DNS_PARSER_TYPE_PTR = function (ab, pack, record) {
-    record.data = unpackLabels(new Uint8Array(ab), record.rdstart, { byteLength: 0, cpcount: 0, labels: [], name: '' }).name;
-    return record;
+  var labelInfo = unpackLabels(new Uint8Array(ab), record.rdstart, { byteLength: 0, cpcount: 0, labels: [], name: '' });
+  if (record.trunc) {
+    throw new Error("RDATA type PTR must be `null`-terminated, not truncated by rdata length.");
+  }
+  record.data = labelInfo.name;
 };
+
 }('undefined' !== typeof window ? window : exports));