Lock the shared fleet key away from the people standing at the bay

The generated install.ps1 wrote the collector key to HKLM\SOFTWARE\GE\ShopDB and
left it at the DACL the key inherits, which grants BUILTIN\Users read. Any
operator logged on to any bay could read the fleet key, and that key still
authenticates an un-enrolled PC: it claims queued commands and downloads script
bodies and installer packages. The per-PC credential work exists to retire that
key, but it stays until every consumer is off it, so meanwhile what matters is
who can read it.

Protect-HklmShopdbKey breaks inheritance, DROPS the inherited entries rather
than copying them - copying is what silently preserves the Users read - and
states SYSTEM and Administrators by SID in both registry views. By SID, so a
localised Windows still matches.

Everything that legitimately reads this key is SYSTEM (the service, the
GE-Enforce reporters) or an administrator (the adoption tool,
Set-ShopDBServerPins.ps1). The tray reads no registry at all - it talks to the
service over the named pipe - so nothing loses access.

It runs for the key-less package too, because ServerPins live in the same key
and the registry is authoritative for pinning: a standard user must not be able
to rewrite the pins either.

A bay that cannot take the ACL still installs. It says so, loudly, rather than
failing the install or staying quiet, because an agent that is not installed is
a worse outcome than a key that is still readable on that one machine.

Note what this does NOT fix: bays that already carry the key keep their
inherited DACL until they are reinstalled or upgraded through a package built
after this change.

tests/test_plugins/test_endpoints_siteagent_build.py

@@ -289,6 +289,62 @@ def test_leaf_certificate_is_imported_into_root(client, db, auth_headers):
     assert json.loads(files['appsettings.json'])['serverpins'] == [leafpin]
 
 
+def test_installer_restricts_the_registry_key_to_system_and_admins(
+        client, db, auth_headers, servercert):
+    """The shared key stays in HKLM until every consumer is on a per-PC
+    credential, so what matters meanwhile is who can read it. The key inherits a
+    DACL that grants BUILTIN\\Users read, which is the exposure the per-PC
+    migration exists to close - the installer must not leave it that way."""
+    files = _files(_build(client, auth_headers, collectorkey=SECRET,
+                          includesharedkey='true'))
+    script = files['install.ps1'].decode('ascii')
+
+    assert 'function Protect-HklmShopdbKey' in script
+    assert 'Protect-HklmShopdbKey -SubKey "SOFTWARE\\GE\\ShopDB"' in script
+    # SYSTEM and Administrators by SID, so a localised Windows still matches.
+    assert '"S-1-5-18", "S-1-5-32-544"' in script
+    # Inheritance broken WITHOUT copying the inherited entries: copying them is
+    # what silently preserves the Users read.
+    assert 'SetAccessRuleProtection($true, $false)' in script
+    assert 'RemoveAccessRule($rule)' in script
+
+
+def test_the_key_is_written_before_it_is_locked(client, db, auth_headers, servercert):
+    """SetAccessControl replaces the DACL rather than merging, so a lock that ran
+    first would be undone by nothing - but a write that ran after a lock the
+    installer no longer holds rights for would fail. Order is the guarantee."""
+    script = _files(_build(client, auth_headers, collectorkey=SECRET,
+                           includesharedkey='true'))['install.ps1'].decode('ascii')
+
+    write = script.index('-Name "CollectorKey" -Value $CollectorKey')
+    lock = script.index('Protect-HklmShopdbKey -SubKey')
+    assert write < lock
+
+
+def test_the_registry_lock_failing_does_not_fail_the_install(
+        client, db, auth_headers, servercert):
+    """A bay that cannot take the ACL still needs its agent. It must say plainly
+    that the key is readable there, rather than dying or staying quiet."""
+    script = _files(_build(client, auth_headers, collectorkey=SECRET,
+                           includesharedkey='true'))['install.ps1'].decode('ascii')
+
+    lock = script.index('Protect-HklmShopdbKey -SubKey')
+    tail = script[lock:lock + 600]
+    assert 'catch' in tail
+    assert 'readable by any logged-on user' in tail
+
+
+def test_the_keyless_package_still_locks_the_key(client, db, auth_headers, servercert):
+    """ServerPins live in the same key and the registry is authoritative for
+    pinning, so a standard user must not be able to rewrite them either."""
+    files = _files(_build(client, auth_headers, collectorkey=SECRET,
+                          includesharedkey=False))
+    script = files['install.ps1'].decode('ascii')
+
+    assert b'CollectorKey' not in files['install.ps1']
+    assert 'Protect-HklmShopdbKey -SubKey "SOFTWARE\\GE\\ShopDB"' in script
+
+
 def test_install_script_helper_without_pins_or_key():
     script = siteagent._install_script('https://shopdb.test', '', 900,
                                        serverpins=[], includesharedkey=False)