push_notifications: Validate format of APNS tokens.

This fixes a bug where we would previously not validate the format of
APNS tokens before writing them to the database, which could lead to
exceptions in the push notifications system if a buggy mobile app
submitted invalid format tokens.

zerver/views/push_notifications.py

@@ -10,42 +10,48 @@ from django.http import HttpRequest, HttpResponse
 from django.utils.translation import ugettext as _
 
 from zerver.lib.push_notifications import add_push_device_token, \
-    remove_push_device_token
+    b64_to_hex, remove_push_device_token
 from zerver.lib.request import has_request_variables, REQ, JsonableError
 from zerver.lib.response import json_success, json_error
 from zerver.lib.validator import check_string, check_list, check_bool
 from zerver.models import PushDeviceToken, UserProfile
 
-def validate_token(token_str):
-    # type: (str) -> None
+def validate_token(token_str, kind):
+    # type: (str, int) -> None
     if token_str == '' or len(token_str) > 4096:
         raise JsonableError(_('Empty or invalid length token'))
+    if kind == PushDeviceToken.APNS:
+        # Validate that we can actually decode the token.
+        try:
+            b64_to_hex(token_str)
+        except Exception:
+            raise JsonableError(_('Invalid APNS token'))
 
 @has_request_variables
 def add_apns_device_token(request, user_profile, token=REQ(),
                           appid=REQ(default=settings.ZULIP_IOS_APP_ID)):
     # type: (HttpRequest, UserProfile, str, str) -> HttpResponse
-    validate_token(token)
+    validate_token(token, PushDeviceToken.APNS)
     add_push_device_token(user_profile, token, PushDeviceToken.APNS, ios_app_id=appid)
     return json_success()
 
 @has_request_variables
 def add_android_reg_id(request, user_profile, token=REQ()):
     # type: (HttpRequest, UserProfile, str) -> HttpResponse
-    validate_token(token)
+    validate_token(token, PushDeviceToken.GCM)
     add_push_device_token(user_profile, token, PushDeviceToken.GCM)
     return json_success()
 
 @has_request_variables
 def remove_apns_device_token(request, user_profile, token=REQ()):
     # type: (HttpRequest, UserProfile, str) -> HttpResponse
-    validate_token(token)
+    validate_token(token, PushDeviceToken.APNS)
     remove_push_device_token(user_profile, token, PushDeviceToken.APNS)
     return json_success()
 
 @has_request_variables
 def remove_android_reg_id(request, user_profile, token=REQ()):
     # type: (HttpRequest, UserProfile, str) -> HttpResponse
-    validate_token(token)
+    validate_token(token, PushDeviceToken.GCM)
     remove_push_device_token(user_profile, token, PushDeviceToken.GCM)
     return json_success()