Allow custom hooks errors to appear in GitLab UI

Error messages from custom pre-receive hooks now appear in the GitLab
UI.

This is re-enabling a feature that had been disabled in merge request
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18646

The feature had been disabled due to security concerns that information
which was not intended to be public (like stack traces) would leak into
public view.

PreReceiveErrors (from pre-receive, post-receive and update custom
hooks) are now filtered for messages that have been prefixed in a
particular way.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/48132

1 files changed, 25 insertions, 6 deletions

diff --git a/lib/gitlab/git/pre_receive_error.rb b/lib/gitlab/git/pre_receive_error.rb
index 03caace6fce..b46d4ba0b02 100644
--- a/lib/gitlab/git/pre_receive_error.rb
+++ b/lib/gitlab/git/pre_receive_error.rb
@@ -4,19 +4,38 @@ module Gitlab
   module Git
     #
     # PreReceiveError is special because its message gets displayed to users
-    # in the web UI. To prevent XSS we sanitize the message on
-    # initialization.
+    # in the web UI. Because of this, we:
+    # - Only display errors that have been marked as safe with a prefix.
+    #   This is to prevent leaking of stacktraces, or other sensitive info.
+    # - Sanitize the string of any XSS
     class PreReceiveError < StandardError
-      def initialize(msg = '')
-        super(nlbr(msg))
+      SAFE_MESSAGE_PREFIXES = [
+        'GitLab:', # Messages from gitlab-shell
+        'GL-HOOK-ERR:' # Messages marked as safe by user
+      ].freeze
+
+      SAFE_MESSAGE_REGEX = /^(#{SAFE_MESSAGE_PREFIXES.join('|')})\s*(?<safe_message>.+)/
+
+      def initialize(message = '')
+        super(sanitize(message))
       end
 
       private
 
       # In gitaly-ruby we override this method to do nothing, so that
       # sanitization happens in gitlab-rails only.
-      def nlbr(str)
-        Gitlab::Utils.nlbr(str)
+      def sanitize(message)
+        return message if message.blank?
+
+        safe_messages = message.split("\n").map do |msg|
+          if (match = msg.match(SAFE_MESSAGE_REGEX))
+            match[:safe_message].presence
+          end
+        end
+
+        safe_messages = safe_messages.compact.join("\n")
+
+        Gitlab::Utils.nlbr(safe_messages)
       end
     end
   end