Merge pull request from GHSA-c2r5-cfqr-c553

* Add hardening monkey-patch to prevent IP spoofing on misconfigured installations

* Remove rack-attack safelist

config/application.rb

@@ -44,6 +44,7 @@ require_relative '../lib/chewy/strategy/bypass_with_warning'
 require_relative '../lib/webpacker/manifest_extensions'
 require_relative '../lib/webpacker/helper_extensions'
 require_relative '../lib/rails/engine_extensions'
+require_relative '../lib/action_dispatch/remote_ip_extensions'
 require_relative '../lib/active_record/database_tasks_extensions'
 require_relative '../lib/active_record/batches'
 require_relative '../lib/simple_navigation/item_extensions'

config/initializers/rack_attack.rb

@@ -62,10 +62,6 @@ class Rack::Attack
     end
   end
 
-  Rack::Attack.safelist('allow from localhost') do |req|
-    req.remote_ip == '127.0.0.1' || req.remote_ip == '::1'
-  end
-
   Rack::Attack.blocklist('deny from blocklist') do |req|
     IpBlock.blocked?(req.remote_ip)
   end

lib/action_dispatch/remote_ip_extensions.rb

@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+# Mastodon is not made to be directly accessed without a reverse proxy.
+# This monkey-patch prevents remote IP address spoofing when being accessed
+# directly.
+#
+# See PR: https://github.com/rails/rails/pull/51610
+
+# In addition to the PR above, it also raises an error if a request with
+# `X-Forwarded-For` or `Client-Ip` comes directly from a client without
+# going through a trusted proxy.
+
+# rubocop:disable all -- This is a mostly vendored file
+
+module ActionDispatch
+  class RemoteIp
+    module GetIpExtensions
+      def calculate_ip
+        # Set by the Rack web server, this is a single value.
+        remote_addr = ips_from(@req.remote_addr).last
+
+        # Could be a CSV list and/or repeated headers that were concatenated.
+        client_ips    = ips_from(@req.client_ip).reverse!
+        forwarded_ips = ips_from(@req.x_forwarded_for).reverse!
+
+        # `Client-Ip` and `X-Forwarded-For` should not, generally, both be set. If they
+        # are both set, it means that either:
+        #
+        # 1) This request passed through two proxies with incompatible IP header
+        #     conventions.
+        #
+        # 2) The client passed one of `Client-Ip` or `X-Forwarded-For`
+        #     (whichever the proxy servers weren't using) themselves.
+        #
+        # Either way, there is no way for us to determine which header is the right one
+        # after the fact. Since we have no idea, if we are concerned about IP spoofing
+        # we need to give up and explode. (If you're not concerned about IP spoofing you
+        # can turn the `ip_spoofing_check` option off.)
+        should_check_ip = @check_ip && client_ips.last && forwarded_ips.last
+        if should_check_ip && !forwarded_ips.include?(client_ips.last)
+          # We don't know which came from the proxy, and which from the user
+          raise IpSpoofAttackError, "IP spoofing attack?! " \
+            "HTTP_CLIENT_IP=#{@req.client_ip.inspect} " \
+            "HTTP_X_FORWARDED_FOR=#{@req.x_forwarded_for.inspect}"
+        end
+
+        # NOTE: Mastodon addition to make sure we don't get requests from a non-trusted client
+        if @check_ip && (forwarded_ips.last || client_ips.last) && !@proxies.any? { |proxy| proxy === remote_addr }
+          raise IpSpoofAttackError, "IP spoofing attack?! client #{remote_addr} is not a trusted proxy " \
+            "HTTP_CLIENT_IP=#{@req.client_ip.inspect} " \
+            "HTTP_X_FORWARDED_FOR=#{@req.x_forwarded_for.inspect}"
+        end
+
+        # We assume these things about the IP headers:
+        #
+        #     - X-Forwarded-For will be a list of IPs, one per proxy, or blank
+        #     - Client-Ip is propagated from the outermost proxy, or is blank
+        #     - REMOTE_ADDR will be the IP that made the request to Rack
+        ips = forwarded_ips + client_ips
+        ips.compact!
+
+        # If every single IP option is in the trusted list, return the IP that's
+        # furthest away
+        filter_proxies([remote_addr] + ips).first || ips.last || remote_addr
+      end
+    end
+  end
+end
+
+ActionDispatch::RemoteIp::GetIp.prepend(ActionDispatch::RemoteIp::GetIpExtensions)
+
+# rubocop:enable all