Check if request is sent from official ownCloud client

There are authentication backends such as Shibboleth that do send no Basic Auth credentials for DAV requests. This means that the ownCloud DAV backend would consider these requests coming from an untrusted source and require higher levels of security checks. (e.g. a CSRF check)

While an elegant solution would rely on authenticating via token (so that one can properly ensure that the request came indeed from a trusted client) this is a okay'ish workaround for this problem until we have something more reliable in the authentication code.

1 files changed, 65 insertions, 17 deletions

diff --git a/apps/dav/lib/connector/sabre/auth.php b/apps/dav/lib/connector/sabre/auth.php
index 8c09c9fdc1c..b63efa3a1ba 100644
--- a/apps/dav/lib/connector/sabre/auth.php
+++ b/apps/dav/lib/connector/sabre/auth.php
@@ -30,6 +30,7 @@
 namespace OCA\DAV\Connector\Sabre;
 
 use Exception;
+use OC\AppFramework\Http\Request;
 use OCP\IRequest;
 use OCP\ISession;
 use OCP\IUserSession;
@@ -48,6 +49,8 @@ class Auth extends AbstractBasic {
 	private $userSession;
 	/** @var IRequest */
 	private $request;
+	/** @var string */
+	private $currentUser;
 
 	/**
 	 * @param ISession $session
@@ -130,7 +133,46 @@ class Auth extends AbstractBasic {
 			$msg = $e->getMessage();
 			throw new ServiceUnavailable("$class: $msg");
 		}
-    }
+	}
+
+	/**
+	 * Checks whether a CSRF check is required on the request
+	 *
+	 * @return bool
+	 */
+	private function requiresCSRFCheck() {
+		// GET requires no check at all
+		if($this->request->getMethod() === 'GET') {
+			return false;
+		}
+
+		// Official ownCloud clients require no checks
+		if($this->request->isUserAgent([
+			Request::USER_AGENT_OWNCLOUD_DESKTOP,
+			Request::USER_AGENT_OWNCLOUD_ANDROID,
+			Request::USER_AGENT_OWNCLOUD_IOS,
+		])) {
+			return false;
+		}
+
+		// If not logged-in no check is required
+		if(!$this->userSession->isLoggedIn()) {
+			return false;
+		}
+
+		// POST always requires a check
+		if($this->request->getMethod() === 'POST') {
+			return true;
+		}
+
+		// If logged-in AND DAV authenticated no check is required
+		if($this->userSession->isLoggedIn() &&
+			$this->isDavAuthenticated($this->userSession->getUser()->getUID())) {
+			return false;
+		}
+
+		return true;
+	}
 
 	/**
 	 * @param RequestInterface $request
@@ -139,27 +181,33 @@ class Auth extends AbstractBasic {
 	 * @throws NotAuthenticated
 	 */
 	private function auth(RequestInterface $request, ResponseInterface $response) {
-		// If request is not GET and not authenticated via WebDAV a requesttoken is required
-		if($this->userSession->isLoggedIn() &&
-			$this->request->getMethod() !== 'GET' &&
-			!$this->isDavAuthenticated($this->userSession->getUser()->getUID())) {
-			if(!$this->request->passesCSRFCheck()) {
+		$forcedLogout = false;
+		if(!$this->request->passesCSRFCheck() &&
+			$this->requiresCSRFCheck()) {
+			// In case of a fail with POST we need to recheck the credentials
+			if($this->request->getMethod() === 'POST') {
+				$forcedLogout = true;
+			} else {
 				$response->setStatus(401);
 				throw new \Sabre\DAV\Exception\NotAuthenticated('CSRF check not passed.');
 			}
 		}
 
-		if (\OC_User::handleApacheAuth() ||
-			//Fix for broken webdav clients
-			($this->userSession->isLoggedIn() && is_null($this->session->get(self::DAV_AUTHENTICATED))) ||
-			//Well behaved clients that only send the cookie are allowed
-			($this->userSession->isLoggedIn() && $this->session->get(self::DAV_AUTHENTICATED) === $this->userSession->getUser()->getUID() && $request->getHeader('Authorization') === null)
-		) {
-			$user = $this->userSession->getUser()->getUID();
-			\OC_Util::setupFS($user);
-			$this->currentUser = $user;
-			$this->session->close();
-			return [true, $this->principalPrefix . $user];
+		if($forcedLogout) {
+			$this->userSession->logout();
+		} else {
+			if (\OC_User::handleApacheAuth() ||
+				//Fix for broken webdav clients
+				($this->userSession->isLoggedIn() && is_null($this->session->get(self::DAV_AUTHENTICATED))) ||
+				//Well behaved clients that only send the cookie are allowed
+				($this->userSession->isLoggedIn() && $this->session->get(self::DAV_AUTHENTICATED) === $this->userSession->getUser()->getUID() && $request->getHeader('Authorization') === null)
+			) {
+				$user = $this->userSession->getUser()->getUID();
+				\OC_Util::setupFS($user);
+				$this->currentUser = $user;
+				$this->session->close();
+				return [true, $this->principalPrefix . $user];
+			}
 		}
 
 		if (!$this->userSession->isLoggedIn() && in_array('XMLHttpRequest', explode(',', $request->getHeader('X-Requested-With')))) {