Add simple clickjacking prevention

Support X-Frame-Options with a default of SAMEORIGIN.

python/nav/django/settings.py

@@ -126,6 +126,7 @@
 
 # Middleware
 MIDDLEWARE = (
+    'django.middleware.clickjacking.XFrameOptionsMiddleware',
     'django.middleware.common.CommonMiddleware',
     'django.contrib.sessions.middleware.SessionMiddleware',
     'nav.web.auth.middleware.AuthenticationMiddleware',
@@ -261,12 +262,14 @@
 # Configured in etc/webfront/webfront.conf:
 #  [security]
 #  needs_tls = yes
+#  frames_allow = self
 
 SECURE_BROWSER_XSS_FILTER = True  # Does no harm
 
 _websecurity_config = WebSecurityConfigParser()
-_needs_tls = bool(_websecurity_config.getboolean('security', 'needs_tls'))
+_needs_tls = bool(_websecurity_config.getboolean('needs_tls'))
 SESSION_COOKIE_SECURE = _needs_tls
+X_FRAME_OPTIONS = _websecurity_config.get_x_frame_options()
 
 # Hack for hackers to use features like debug_toolbar etc.
 # https://code.djangoproject.com/wiki/SplitSettings (Rob Golding's method)

python/nav/web/security.py

@@ -1,11 +1,27 @@
 from pathlib import Path
 
-from nav.config import NAVConfigParser
+from nav.config import NavConfigParserDefaultSection
 
 
-class WebSecurityConfigParser(NAVConfigParser):
+class WebSecurityConfigParser(NavConfigParserDefaultSection):
+    SECTION = "security"
     DEFAULT_CONFIG_FILES = [str(Path('webfront') / 'webfront.conf')]
     DEFAULT_CONFIG = u"""
 [security]
 needs_tls=no
+allow_frames=self
 """
+    FRAMES_OPTION = 'allow_frames'
+    FRAMES_DEFAULT = 'self'
+
+    def __init__(self):
+        super().__init__(self.SECTION)
+
+    # clickjacking-settings
+
+    def get_x_frame_options(self):
+        "Translate CSP frame ancestors to the old X-Frame-Options header"
+        frames_flag = self.get(self.FRAMES_OPTION) or self.FRAMES_DEFAULT
+        if frames_flag == 'none':
+            return 'DENY'
+        return 'SAMEORIGIN'