fix: Improved dnshack to catch all problematic dns.lookup requests

Hypfer · Aug 12, 2020 · 8609612 · 8609612
1 parent 252c22d
commit 8609612
Showing 1 changed file with 30 additions and 21 deletions.
diff --git a/lib/DnsHack.js b/lib/DnsHack.js
@@ -11,9 +11,8 @@ const Logger = require("./Logger");
     Simply resolving any hostnames before connecting to them isn't an option though,
     since then certificate validation will fail.
 
-    Therefore, the only way to mitigate this is to overwrite dns.lookup and redirect all calls that
-    look the same as the call of the mqtt library.
-
+    Therefore, the only way to mitigate this is to overwrite dns.lookup and redirect all calls of the MQTT client
+    by looking at the stacktrace of the call.
 
     I'm sorry.
  */
@@ -28,25 +27,35 @@ dns.lookup = function lookupResolveHack(hostname, options, callback) {
 
     if (
         Object.getOwnPropertyNames(options).length === 2 &&
-        options.family === undefined && options.hints === 0
+        options.family === undefined
     ) {
-        Logger.trace("Intercepting dns.lookup call for", hostname);
-
-        dns.resolve4(hostname, (err, addresses) => {
-            if (err && err.code === "ENOTFOUND") {
-                dns.resolve6(hostname, (err, addresses) => {
-                    if (err) {
-                        callback(err);
-                    } else {
-                        callback(null, addresses[0], 6);
-                    }
-                });
-            } else if (err) {
-                callback(err);
-            } else {
-                callback(null, addresses[0], 4);
-            }
-        });
+        //This sorta looks like something that might be a request from the MQTT client
+        //Time to take a look at the stacktrace to make sure
+        //Doing this after checking the previous condition saves us from creating a stacktrace
+        //on each udp send which would be horrible for the performance
+        const stack = new Error().stack;
+
+        if (stack.includes("lookupAndConnect")) { //nodejs internal function
+            Logger.trace("Intercepting dns.lookup call for", hostname);
+
+            dns.resolve4(hostname, (err, addresses) => {
+                if (err && err.code === "ENOTFOUND") {
+                    dns.resolve6(hostname, (err, addresses) => {
+                        if (err) {
+                            callback(err);
+                        } else {
+                            callback(null, addresses[0], 6);
+                        }
+                    });
+                } else if (err) {
+                    callback(err);
+                } else {
+                    callback(null, addresses[0], 4);
+                }
+            });
+        } else {
+            return realLookup(hostname, options, callback);
+        }
     } else {
         return realLookup(hostname, options, callback);
     }