Block install without CAN_INSTALL file

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

core/Controller/SetupController.php

 			$post['dbpass'] = $post['dbpassword'];
 		}
 
+		if (!is_file(\OC::$configDir.'/CAN_INSTALL')) {
+			$this->displaySetupForbidden();
+			return;
+		}
+
 		if(isset($post['install']) AND $post['install']=='true') {
 			// We have to launch the installation process :
 			$e = $this->setupHelper->install($post);
 		}
 	}
 
+	private function displaySetupForbidden() {
+		\OC_Template::printGuestPage('', 'installation_forbidden');
+	}
+
 	public function display($post) {
 		$defaults = array(
 			'adminlogin' => '',
 			unlink($this->autoConfigFile);
 		}
 		\OC::$server->getIntegrityCodeChecker()->runInstanceVerification();
+
+		if (\OC_Util::getChannel() !== 'git' && is_file(\OC::$configDir.'/CAN_INSTALL')) {
+			if (!unlink(\OC::$configDir.'/CAN_INSTALL')) {
+				\OC_Template::printGuestPage('', 'installation_incomplete');
+			}
+		}
+
 		\OC_Util::redirectToDefaultPage();
 	}
 

core/templates/installation_forbidden.php

+<div class="error">
+	<h2><?php p($l->t('Error')) ?></h2>
+	<p>
+		<?php p($l->t('It looks like you are trying to reinstall your Nextcloud. However the file CAN_INSTALL is missing from your config directory. Please create the file CAN_INSTALL in your config folder to continue.')) ?>
+	</p>
+</div>

core/templates/installation_incomplete.php

+<div class="error">
+	<h2><?php p($l->t('Error')) ?></h2>
+	<p>
+		<?php p($l->t('Could not remove CAN_INSTALL from the config folder. Please remove this file manually.')) ?>
+	</p>
+</div>

lib/private/Updater.php

 			$this->emit('\OC\Updater', 'maintenanceEnabled');
 		}
 
+		// Clear CAN_INSTALL file if not on git
+		if (\OC_Util::getChannel() !== 'git' && is_file(\OC::$configDir.'/CAN_INSTALL')) {
+			if (!unlink(\OC::$configDir . '/CAN_INSTALL')) {
+				$this->log->error('Could not cleanup CAN_INSTALL from your config folder. Please remove this file manually.');
+			}
+		}
+
 		$installedVersion = $this->config->getSystemValue('version', '0.0.0');
 		$currentVersion = implode('.', \OCP\Util::getVersion());