From cdabc95608336dbea7b6a3a3e925de5bbd5313ba Mon Sep 17 00:00:00 2001
From: Andrew White <andyw@pixeltrix.co.uk>
Date: Fri, 27 Nov 2015 13:46:46 +0000
Subject: [PATCH] Don't short-circuit reject_if proc

When updating an associated record via nested attribute hashes the
reject_if proc could be bypassed if the _destroy flag was set in the
attribute hash and allow_destroy was set to false.

The fix is to only short-circuit if the _destroy flag is set and the
option allow_destroy is set to true. It also fixes an issue where
a new record wasn't created if _destroy was set and the option
allow_destroy was set to false.

CVE-2015-7577
---
 activerecord/lib/active_record/nested_attributes.rb | 14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/activerecord/lib/active_record/nested_attributes.rb b/activerecord/lib/active_record/nested_attributes.rb
index 41b62f6..a0e98c3 100644
--- a/activerecord/lib/active_record/nested_attributes.rb
+++ b/activerecord/lib/active_record/nested_attributes.rb
@@ -445,11 +445,12 @@ def has_destroy_flag?(hash)
     # has_destroy_flag? or if a <tt>:reject_if</tt> proc exists for this
     # association and evaluates to +true+.
     def reject_new_record?(association_name, attributes)
-      has_destroy_flag?(attributes) || call_reject_if(association_name, attributes)
+      will_be_destroyed?(association_name, attributes) || call_reject_if(association_name, attributes)
     end
 
     def call_reject_if(association_name, attributes)
-      return false if has_destroy_flag?(attributes)
+      return false if will_be_destroyed?(association_name, attributes)
+
       case callback = self.nested_attributes_options[association_name][:reject_if]
       when Symbol
         method(callback).arity == 0 ? send(callback) : send(callback, attributes)
@@ -458,6 +459,15 @@ def call_reject_if(association_name, attributes)
       end
     end
 
+    # Only take into account the destroy flag if <tt>:allow_destroy</tt> is true
+    def will_be_destroyed?(association_name, attributes)
+      allow_destroy?(association_name) && has_destroy_flag?(attributes)
+    end
+
+    def allow_destroy?(association_name)
+      self.nested_attributes_options[association_name][:allow_destroy]
+    end
+
     def raise_nested_attributes_record_not_found(association_name, record_id)
       raise RecordNotFound, "Couldn't find #{self.class.reflect_on_association(association_name).klass.name} with ID=#{record_id} for #{self.class.name} with ID=#{id}"
     end