Fix a memory leak caused by Banzai::Filter::SanitizationFilter

In Banzai::Filter::SanitizationFilter#customize_whitelist, we append
three lambdas that has reference to the SanitizationFilter instance,
which in turn (potentially) has a reference to the following chain:

context hash -> Project instance -> Repository instance -> lookup hash
-> various Rugged instances -> various mmap-ed git pack files.

All of the above is not garbage collected because the array we append
the lambdas to is the constant
HTML::Pipeline::SanitizationFilter::WHITELIST.

1 files changed, 3 insertions, 1 deletions

diff --git a/lib/banzai/filter/sanitization_filter.rb b/lib/banzai/filter/sanitization_filter.rb
index ca80aac5a08..6e13282d5f4 100644
--- a/lib/banzai/filter/sanitization_filter.rb
+++ b/lib/banzai/filter/sanitization_filter.rb
@@ -7,7 +7,7 @@ module Banzai
       UNSAFE_PROTOCOLS = %w(data javascript vbscript).freeze
 
       def whitelist
-        whitelist = super
+        whitelist = super.dup
 
         customize_whitelist(whitelist)
 
@@ -42,6 +42,8 @@ module Banzai
         # Allow any protocol in `a` elements...
         whitelist[:protocols].delete('a')
 
+        whitelist[:transformers] = whitelist[:transformers].dup
+
         # ...but then remove links with unsafe protocols
         whitelist[:transformers].push(remove_unsafe_links)