net: handle undefined parent in _unrefTimer and _destroy

The fix and approach are from #64491 by Shivay-98; this reopens it to
get it landed, since the original stalled awaiting requested changes.

`Socket.prototype._unrefTimer` and `Socket.prototype._destroy` both walk
the `_parent` chain with a strict `!== null` check. During connection
teardown a socket's `_parent` can be left `undefined` (for example a TLS
socket layered over another stream), so the loop steps onto `undefined`
and reads a property off it, throwing a TypeError:

    Cannot read properties of undefined (reading 'Symbol(timeout)')

from an uncaught I/O callback and crashing the process.

Using a nullish (`!= null`) check terminates the walk on both `null` and
`undefined`.

[petter@hightouch.io: apply the same fix to the identical loop in
`_destroy`, which the original regression test already exercised via
`destroy()`; add direct unit coverage for both paths.]

Fixes: https://github.com/nodejs/node/issues/64490
Refs: https://github.com/nodejs/node/pull/64491

Signed-off-by: Petter Häggholm <petter@hightouch.io>
PR-URL: https://github.com/nodejs/node/pull/64644
Fixes: https://github.com/nodejs/node/issues/64490
Refs: https://github.com/nodejs/node/pull/64491
Reviewed-By: Tim Perry <pimterry@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ethan Arrowood <ethan@arrowood.dev>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/net.js

@@ -740,7 +740,9 @@ ObjectSetPrototypeOf(Socket, stream.Duplex);
 
 // Refresh existing timeouts.
 Socket.prototype._unrefTimer = function _unrefTimer() {
-  for (let s = this; s !== null; s = s._parent) {
+  // `_parent` may be null; we use a loose `!= null` check in case external
+  // code sets it to undefined.
+  for (let s = this; s != null; s = s._parent) {
     if (s[kTimeout])
       s[kTimeout].refresh();
   }
@@ -1101,7 +1103,9 @@ Socket.prototype._destroy = function(exception, cb) {
 
   this.connecting = false;
 
-  for (let s = this; s !== null; s = s._parent) {
+  // `_parent` may be null; we use a loose `!= null` check in case external
+  // code sets it to undefined.
+  for (let s = this; s != null; s = s._parent) {
     clearTimeout(s[kTimeout]);
   }
 

test/parallel/test-net-socket-unref-timer-parent-chain.js

@@ -0,0 +1,25 @@
+'use strict';
+const common = require('../common');
+
+// Walking the `_parent` chain must stop on a nullish link, not only strict
+// `null`. During connection teardown a socket's `_parent` can be left
+// `undefined`, which previously caused `_unrefTimer()` and `_destroy()` to read
+// a property off `undefined` and throw.
+// Refs: https://github.com/nodejs/node/issues/64490
+
+const assert = require('assert');
+const net = require('net');
+
+{
+  const socket = new net.Socket();
+  socket._parent = undefined;
+  socket._unrefTimer();
+}
+
+{
+  const socket = new net.Socket();
+  socket._parent = undefined;
+  socket.on('error', common.mustNotCall());
+  socket.destroy();
+  assert.strictEqual(socket.destroyed, true);
+}

test/parallel/test-net-unref-timer-parent-undefined.js

@@ -0,0 +1,39 @@
+'use strict';
+
+const common = require('../common');
+
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+const tls = require('tls');
+const fixtures = require('../common/fixtures');
+
+// A TLS socket whose `_parent` is left `undefined` during teardown must not
+// crash when reads land on it (`onStreamRead` -> `_unrefTimer`) or when it is
+// destroyed (`_destroy`). Both walk the `_parent` chain.
+// Refs: https://github.com/nodejs/node/issues/64490
+
+const options = {
+  key: fixtures.readKey('agent1-key.pem'),
+  cert: fixtures.readKey('agent1-cert.pem'),
+};
+
+const server = tls.createServer(options, common.mustCall((conn) => {
+  setTimeout(() => conn.write('x'), 50);
+}));
+
+server.listen(0, common.mustCall(() => {
+  const client = tls.connect({
+    port: server.address().port,
+    rejectUnauthorized: false,
+  }, common.mustCall(() => {
+    client._parent = undefined;
+  }));
+
+  client.on('data', common.mustCall(() => {
+    server.close();
+    client.destroy();
+  }));
+
+  client.on('error', common.mustNotCall());
+}));