Return a copy of the cache entry when local_cache exists:

- When the local cache exists (during the request lifecycle), the
  entry returned from the LocalStore is passed as a reference which
  means mutable object can accidentaly get modified.

  This behaviour seems unnecessarily unsafe and is prone to
  issues like it happened in our application.

  This patch dup the `Entry` returned from the cache and dup it's
  internal value.

1 files changed, 4 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/cache/strategy/local_cache.rb b/activesupport/lib/active_support/cache/strategy/local_cache.rb
index 39b32fc7f6..4ca084163b 100644
--- a/activesupport/lib/active_support/cache/strategy/local_cache.rb
+++ b/activesupport/lib/active_support/cache/strategy/local_cache.rb
@@ -75,7 +75,10 @@ module ActiveSupport
           end
 
           def fetch_entry(key, options = nil) # :nodoc:
-            @data.fetch(key) { @data[key] = yield }
+            entry = @data.fetch(key) { @data[key] = yield }
+            dup_entry = entry.dup
+            dup_entry&.dup_value!
+            dup_entry
           end
         end