dns: improve setServers() errors and performance

Issue 1: make invalid setServers yield uniform error

Behavior:
dns.setServers throws a null pointer dereference on some inputs.
Expected behavior was the more pleasant
  TypeError [ERR_INVALID_IP_ADDRESS] ...

Root cause(s?):
- Dereferencing the result of a regex match without confirming
  that there was a match.
- assuming the capture of an optional group (?)

Solution:
Confirm the match, and handle a missing port cleanly.

Tests: I added tests for various unusual inputs.

Issue 2: revise quadratic regex in setServers

Problem:
The IPv6 regex was quadratic.
On long malicious input the event loop could block.

The security team did not deem it a security risk,
but said a PR was welcome.

Solution:
Revise the regex to a linear-complexity version.

Tests:
I added REDOS tests to the "oddities" section.

Fixes: #20441
Fixes: #20443

PR-URL: #20445
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/dns.js

@@ -289,7 +289,7 @@ function setServers(servers) {
   // servers cares won't have any servers available for resolution
   const orig = this._handle.getServers();
   const newSet = [];
-  const IPv6RE = /\[(.*)\]/;
+  const IPv6RE = /^\[([^[\]]*)\]/;
   const addrSplitRE = /(^.+?)(?::(\d+))?$/;
 
   servers.forEach((serv) => {
@@ -309,11 +309,16 @@ function setServers(servers) {
       }
     }
 
-    const [, s, p] = serv.match(addrSplitRE);
-    ipVersion = isIP(s);
+    // addr::port
+    const addrSplitMatch = serv.match(addrSplitRE);
+    if (addrSplitMatch) {
+      const hostIP = addrSplitMatch[1];
+      const port = addrSplitMatch[2] || IANA_DNS_PORT;
 
-    if (ipVersion !== 0) {
-      return newSet.push([ipVersion, s, parseInt(p)]);
+      ipVersion = isIP(hostIP);
+      if (ipVersion !== 0) {
+        return newSet.push([ipVersion, hostIP, parseInt(port)]);
+      }
     }
 
     throw new ERR_INVALID_IP_ADDRESS(serv);

test/parallel/test-dns.js

@@ -62,6 +62,31 @@ assert(existing.length > 0);
   ]);
 }
 
+{
+  // Various invalidities, all of which should throw a clean error.
+  const invalidServers = [
+    ' ',
+    '\n',
+    '\0',
+    '1'.repeat(3 * 4),
+    // Check for REDOS issues.
+    ':'.repeat(100000),
+    '['.repeat(100000),
+    '['.repeat(100000) + ']'.repeat(100000) + 'a'
+  ];
+  invalidServers.forEach((serv) => {
+    assert.throws(
+      () => {
+        dns.setServers([serv]);
+      },
+      {
+        name: 'TypeError [ERR_INVALID_IP_ADDRESS]',
+        code: 'ERR_INVALID_IP_ADDRESS'
+      }
+    );
+  });
+}
+
 const goog = [
   '8.8.8.8',
   '8.8.4.4',