[FIX] base: strengthen ir.attachment access rights

An ir.attachment record can be served as a request's reponse if:
  - a request triggers a 404
  - the ir.attachment record has its url field matching the url of
    the failed and is of binary type

Following rev[1], portal users have the right to create these kind of
records, and it is a security concern.

This patch restrict the ability to create and write on the ir.attachment
records that may be served through the dispatch's exception mechanism to
settings users.

As the asset bundles files are served through the use of these special
ir.attachment, we make sure to retrieve only ir.attachment records
created by the superuser in the `get_attachment` method.

As website administrators often need to play with these special
ir.attachment, we also let to this group the permission to manage them.

[1] 61065b6d04

addons/website/models/ir_attachment.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
-from odoo import fields, models
+from odoo import api, fields, models
 
 
 class Attachment(models.Model):
@@ -10,3 +10,7 @@ class Attachment(models.Model):
 
     # related for backward compatibility with saas-6
     website_url = fields.Char(string="Attachment URL", related='local_url', deprecated=True)
+
+    @api.model
+    def get_serving_groups(self):
+        return super(Attachment, self).get_serving_groups() + ['website.group_website_designer']

odoo/addons/base/ir/ir_attachment.py

@@ -11,7 +11,7 @@ from collections import defaultdict
 import uuid
 
 from odoo import api, fields, models, tools, SUPERUSER_ID, _
-from odoo.exceptions import AccessError
+from odoo.exceptions import AccessError, ValidationError
 from odoo.tools import config, human_size, ustr, html_escape
 from odoo.tools.mimetypes import guess_mimetype
 
@@ -263,6 +263,15 @@ class IrAttachment(models.Model):
                 index_content = b"\n".join(words).decode('ascii')
         return index_content
 
+    @api.model
+    def get_serving_groups(self):
+        """ An ir.attachment record may be used as a fallback in the
+        http dispatch if its type field is set to "binary" and its url
+        field is set as the request's url. Only the groups returned by
+        this method are allowed to create and write on such records.
+        """
+        return ['base.group_system']
+
     name = fields.Char('Attachment Name', required=True)
     datas_fname = fields.Char('File Name')
     description = fields.Text('Description')
@@ -299,6 +308,16 @@ class IrAttachment(models.Model):
                            self._table, ['res_model', 'res_id'])
         return res
 
+    @api.one
+    @api.constrains('type', 'url')
+    def _check_serving_attachments(self):
+        # restrict writing on attachments that could be served by the
+        # ir.http's dispatch exception handling
+        if self.type == 'binary' and self.url:
+            has_group = self.env.user.has_group
+            if not any([has_group(g) for g in self.get_serving_groups()]):
+                raise ValidationError("Sorry, you are not allowed to write on this document")
+
     @api.model
     def check(self, mode, values=None):
         """Restricts the access to an ir.attachment, according to referred model

odoo/addons/base/ir/ir_qweb/assetsbundle.py

@@ -10,7 +10,7 @@ import uuid
 from datetime import datetime
 from subprocess import Popen, PIPE
 from collections import OrderedDict
-from odoo import fields, tools
+from odoo import fields, tools, SUPERUSER_ID
 from odoo.tools.pycompat import string_types, to_text
 from odoo.http import request
 from odoo.modules.module import get_resource_path
@@ -230,10 +230,11 @@ class AssetsBundle(object):
         self.env.cr.execute("""
              SELECT max(id)
                FROM ir_attachment
-              WHERE url like %s
+              WHERE create_uid = %s
+                AND url like %s
            GROUP BY datas_fname
            ORDER BY datas_fname
-         """, [url_pattern])
+         """, [SUPERUSER_ID, url_pattern])
         attachment_ids = [r[0] for r in self.env.cr.fetchall()]
         return self.env['ir.attachment'].sudo().browse(attachment_ids)