Security: Remember hosts with ignored cert errors for load status

Without this change, we only set a flag when a certificate error occurred.
However, when the same certificate error then happens a second time (e.g.
because of a reload or opening the same URL again), we then colored the URL as
success_https (i.e. green) again.

See #5403

(cherry picked from commit 021ab57)

qutebrowser/browser/browsertab.py

@@ -867,6 +867,13 @@ class AbstractTab(QWidget):
     # arg 1: The exit code.
     renderer_process_terminated = pyqtSignal(TerminationStatus, int)
 
+    # Hosts for which a certificate error happened. Shared between all tabs.
+    #
+    # Note that we remember hosts here, without scheme/port:
+    # QtWebEngine/Chromium also only remembers hostnames, and certificates are
+    # for a given hostname anyways.
+    _insecure_hosts = set()  # type: typing.Set[str]
+
     def __init__(self, *, win_id: int, private: bool,
                  parent: QWidget = None) -> None:
         self.is_private = private
@@ -884,7 +891,6 @@ def __init__(self, *, win_id: int, private: bool,
         self._layout = miscwidgets.WrapperLayout(self)
         self._widget = typing.cast(QWidget, None)
         self._progress = 0
-        self._has_ssl_errors = False
         self._load_status = usertypes.LoadStatus.none
         self._tab_event_filter = eventfilter.TabEventFilter(
             self, parent=self)
@@ -971,7 +977,6 @@ def _on_url_changed(self, url: QUrl) -> None:
     @pyqtSlot()
     def _on_load_started(self) -> None:
         self._progress = 0
-        self._has_ssl_errors = False
         self.data.viewing_source = False
         self._set_load_status(usertypes.LoadStatus.loading)
         self.load_started.emit()
@@ -1030,9 +1035,12 @@ def _update_load_status(self, ok: bool) -> None:
         Needs to be called by subclasses to trigger a load status update, e.g.
         as a response to a loadFinished signal.
         """
-        if ok and not self._has_ssl_errors:
+        if ok:
             if self.url().scheme() == 'https':
-                self._set_load_status(usertypes.LoadStatus.success_https)
+                if self.url().host() in self._insecure_hosts:
+                    self._set_load_status(usertypes.LoadStatus.warn)
+                else:
+                    self._set_load_status(usertypes.LoadStatus.success_https)
             else:
                 self._set_load_status(usertypes.LoadStatus.success)
         elif ok:

qutebrowser/browser/webengine/webenginetab.py

@@ -1428,9 +1428,9 @@ def _on_load_finished(self, ok: bool) -> None:
 
     @pyqtSlot(certificateerror.CertificateErrorWrapper)
     def _on_ssl_errors(self, error):
-        self._has_ssl_errors = True
-
         url = error.url()
+        self._insecure_hosts.add(url.host())
+
         log.webview.debug("Certificate error: {}".format(error))
 
         if error.is_overridable():

qutebrowser/browser/webkit/webkittab.py

@@ -847,9 +847,9 @@ def _on_navigation_request(self, navigation):
         if navigation.is_main_frame:
             self.settings.update_for_url(navigation.url)
 
-    @pyqtSlot()
-    def _on_ssl_errors(self):
-        self._has_ssl_errors = True
+    @pyqtSlot('QNetworkReply*')
+    def _on_ssl_errors(self, reply):
+        self._insecure_hosts.add(reply.url().host())
 
     def _connect_signals(self):
         view = self._widget