login: Prevent multiple logins in a single browser session

unless allowed by cockpit.conf.

If the login page is loaded and a valid session cookie is already
available, then we are about to log into a second host from the same
browser session, and both logins will have access to each others
cookies. This should only be allowed when AllowMultiHost is true. If
it is not true, the login page immediately redirects to the session
for the existing cookie.

Information about session cookies is not available to login.js, so
cockpit-ws helps out by exposing which ones are present, without
exposing the cookies themselves.

pkg/static/login.js

@@ -338,6 +338,26 @@ import "./login.scss";
         event.stopPropagation();
     }
 
+    function deal_with_multihost() {
+        // If we are currently logged in to some machine, but still
+        // end up on the login page, we are about to load resources
+        // from two machines into the same browser origin. This needs
+        // to be allowed explicitly via a configuration setting.
+
+        const logged_into = environment.logged_into || [];
+        const cur_machine = logged_into.length > 0 ? logged_into[0] : null;
+
+        function redirect_to_current_machine() {
+            if (cur_machine === ".")
+                login_reload("/");
+            else
+                login_reload("/=" + cur_machine);
+        }
+
+        if (cur_machine && !environment.page.allow_multihost)
+            redirect_to_current_machine();
+    }
+
     function boot() {
         window.onload = null;
 
@@ -348,6 +368,8 @@ import "./login.scss";
                 document.documentElement.dir = window.cockpit_po[""]["language-direction"];
         }
 
+        deal_with_multihost();
+
         setup_path_globals(window.location.pathname);
 
         /* Determine if we are nested or not, and switch styles */

src/ws/cockpitauth.c

@@ -1241,13 +1241,38 @@ base64_decode_string (const char *enc)
   return dec;
 }
 
+static CockpitSession *
+session_for_cookie_value (CockpitAuth *self,
+                          const gchar *cookie_value)
+{
+  gchar *decoded = NULL;
+  const char *prefix = "v=2;k=";
+  CockpitSession *ret = NULL;
+
+  g_return_val_if_fail (self != NULL, FALSE);
+
+  if (cookie_value)
+    {
+      decoded = base64_decode_string (cookie_value);
+      if (decoded != NULL)
+        {
+          if (g_str_has_prefix (decoded, prefix))
+            ret = g_hash_table_lookup (self->sessions, decoded);
+          else
+            g_debug ("invalid or unsupported cookie: %s", decoded);
+
+          g_free (decoded);
+        }
+    }
+
+  return ret;
+}
+
 static CockpitSession *
 session_for_request (CockpitAuth *self,
                      CockpitWebRequest *request)
 {
-  gchar *cookie = NULL;
   gchar *raw = NULL;
-  const char *prefix = "v=2;k=";
   CockpitSession *ret = NULL;
   gchar *application;
   gchar *cookie_name = NULL;
@@ -1260,23 +1285,12 @@ session_for_request (CockpitAuth *self,
 
   cookie_name = application_cookie_name (application);
   raw = cockpit_web_request_parse_cookie (request, cookie_name);
-  if (raw)
-    {
-      cookie = base64_decode_string (raw);
-      if (cookie != NULL)
-        {
-          if (g_str_has_prefix (cookie, prefix))
-            ret = g_hash_table_lookup (self->sessions, cookie);
-          else
-            g_debug ("invalid or unsupported cookie: %s", cookie);
+  ret = session_for_cookie_value (self, raw);
 
-          /* We must never find the default session based on a cookie */
-          g_assert (!ret || !g_str_equal (ret->cookie, LOCAL_SESSION));
-          g_assert (!ret || !g_str_equal (ret->name, LOCAL_SESSION));
-          g_free (cookie);
-        }
-      g_free (raw);
-    }
+  /* We must never find the default session based on a cookie */
+  g_assert (!ret || !g_str_equal (ret->cookie, LOCAL_SESSION));
+  g_assert (!ret || !g_str_equal (ret->name, LOCAL_SESSION));
+  g_free (raw);
 
   /* Check for a default session for auto-login */
   if (!ret)
@@ -1309,6 +1323,13 @@ cockpit_auth_check_cookie (CockpitAuth *self,
     }
 }
 
+gboolean
+cockpit_auth_is_valid_cookie_value (CockpitAuth *self,
+                                    const gchar *cookie_value)
+{
+  return session_for_cookie_value (self, cookie_value) != NULL;
+}
+
 void
 cockpit_auth_local_async (CockpitAuth *self,
                           const gchar *user,

src/ws/cockpitauth.h

@@ -102,7 +102,10 @@ gboolean        cockpit_auth_local_finish    (CockpitAuth *self,
 CockpitWebService *  cockpit_auth_check_cookie    (CockpitAuth *self,
                                                    CockpitWebRequest *request);
 
-gchar *         cockpit_auth_parse_application    (const gchar *path,
+gboolean        cockpit_auth_is_valid_cookie_value (CockpitAuth *self,
+                                                    const gchar *cookie_value);
+
+  gchar *         cockpit_auth_parse_application    (const gchar *path,
                                                    gboolean *is_host);
 
 gchar *         cockpit_auth_empty_cookie_value       (const gchar *path,

src/ws/cockpithandlers.c

@@ -277,8 +277,47 @@ add_page_to_environment (JsonObject *object,
   json_object_set_object_member (object, "page", page);
 }
 
+static void
+add_logged_into_to_environment (JsonObject *object,
+                                CockpitAuth *auth,
+                                GHashTable *request_headers)
+{
+  JsonArray *logged_into = json_array_new ();
+
+  gchar *h = g_hash_table_lookup (request_headers, "Cookie");
+  while (h && *h) {
+    const gchar *start = h;
+    while (*h && *h != '=')
+      h++;
+    const gchar *equal = h;
+    while (*h && *h != ';')
+      h++;
+    const gchar *end = h;
+    if (*h)
+      h++;
+    while (*h && *h == ' ')
+      h++;
+
+    if (*equal != '=')
+      continue;
+
+    g_autofree gchar *value = g_strndup (equal + 1, end - equal - 1);
+
+    if (!cockpit_auth_is_valid_cookie_value (auth, value))
+      continue;
+
+    g_autofree gchar *name = g_strndup (start, equal - start);
+    if (g_str_equal (name, "cockpit"))
+      json_array_add_string_element(logged_into, ".");
+    else if (g_str_has_prefix (name, "machine-cockpit+"))
+      json_array_add_string_element(logged_into, name + strlen("machine-cockpit+"));
+  }
+
+  json_object_set_array_member (object, "logged_into", logged_into);
+}
+
 static GBytes *
-build_environment (GHashTable *os_release)
+build_environment (GHashTable *os_release, CockpitAuth *auth, GHashTable *request_headers)
 {
   /*
    * We don't include entirety of os-release into the
@@ -310,6 +349,7 @@ build_environment (GHashTable *os_release)
   json_object_set_boolean_member (object, "is_cockpit_client", is_cockpit_client);
 
   add_page_to_environment (object, is_cockpit_client);
+  add_logged_into_to_environment (object, auth, request_headers);
 
   hostname = g_malloc0 (HOST_NAME_MAX + 1);
   gethostname (hostname, HOST_NAME_MAX);
@@ -386,7 +426,7 @@ send_login_html (CockpitWebResponse *response,
   GBytes *po_bytes;
   CockpitWebFilter *filter3 = NULL;
 
-  environment = build_environment (ws->os_release);
+  environment = build_environment (ws->os_release, ws->auth, headers);
   filter = cockpit_web_inject_new (marker, environment, 1);
   g_bytes_unref (environment);
   cockpit_web_response_add_filter (response, filter);
@@ -455,6 +495,7 @@ send_login_html (CockpitWebResponse *response,
                                     "Content-Security-Policy", content_security_policy,
                                     "Set-Cookie", cookie_line,
                                     NULL);
+      cockpit_web_response_set_cache_type (response, COCKPIT_WEB_RESPONSE_NO_CACHE);
       if (cockpit_web_response_queue (response, bytes))
         cockpit_web_response_complete (response);