1 files changed, 53 insertions, 4 deletions

diff --git a/ext/psych/lib/psych.rb b/ext/psych/lib/psych.rb
index 66a0641f39..711b3c1377 100644
--- a/ext/psych/lib/psych.rb
+++ b/ext/psych/lib/psych.rb
@@ -246,6 +246,55 @@ module Psych
   end
 
   ###
+  # Safely load the yaml string in +yaml+.  By default, only the following
+  # classes are allowed to be deserialized:
+  #
+  # * TrueClass
+  # * FalseClass
+  # * NilClass
+  # * Numeric
+  # * String
+  # * Array
+  # * Hash
+  #
+  # Recursive data structures are not allowed by default.  Arbitrary classes
+  # can be allowed by adding those classes to the +whitelist+.  They are
+  # additive.  For example, to allow Date deserialization:
+  #
+  #   Psych.safe_load(yaml, [Date])
+  #
+  # Now the Date class can be loaded in addition to the classes listed above.
+  #
+  # Aliases can be explicitly allowed by changing the +aliases+ parameter.
+  # For example:
+  #
+  #   x = []
+  #   x << x
+  #   yaml = Psych.dump x
+  #   Psych.safe_load yaml               # => raises an exception
+  #   Psych.safe_load yaml, [], [], true # => loads the aliases
+  #
+  # A Psych::DisallowedClass exception will be raised if the yaml contains a
+  # class that isn't in the whitelist.
+  #
+  # A Psych::BadAlias exception will be raised if the yaml contains aliases
+  # but the +aliases+ parameter is set to false.
+  def self.safe_load yaml, whitelist_classes = [], whitelist_symbols = [], aliases = false, filename = nil
+    result = parse(yaml, filename)
+    return unless result
+
+    class_loader = ClassLoader::Restricted.new(whitelist_classes.map(&:to_s),
+                                               whitelist_symbols.map(&:to_s))
+    scanner      = ScalarScanner.new class_loader
+    if aliases
+      visitor = Visitors::ToRuby.new scanner, class_loader
+    else
+      visitor = Visitors::NoAliasRuby.new scanner, class_loader
+    end
+    visitor.accept result
+  end
+
+  ###
   # Parse a YAML string in +yaml+.  Returns the Psych::Nodes::Document.
   # +filename+ is used in the exception message if a Psych::SyntaxError is
   # raised.
@@ -355,7 +404,7 @@ module Psych
       io      = nil
     end
 
-    visitor = Psych::Visitors::YAMLTree.new options
+    visitor = Psych::Visitors::YAMLTree.create options
     visitor << o
     visitor.tree.yaml io, options
   end
@@ -367,7 +416,7 @@ module Psych
   #
   #   Psych.dump_stream("foo\n  ", {}) # => "--- ! \"foo\\n  \"\n--- {}\n"
   def self.dump_stream *objects
-    visitor = Psych::Visitors::YAMLTree.new {}
+    visitor = Psych::Visitors::YAMLTree.create({})
     objects.each do |o|
       visitor << o
     end
@@ -377,7 +426,7 @@ module Psych
   ###
   # Dump Ruby +object+ to a JSON string.
   def self.to_json object
-    visitor = Psych::Visitors::JSONTree.new
+    visitor = Psych::Visitors::JSONTree.create
     visitor << object
     visitor.tree.yaml
   end
@@ -435,7 +484,7 @@ module Psych
   @load_tags = {}
   @dump_tags = {}
   def self.add_tag tag, klass
-    @load_tags[tag] = klass
+    @load_tags[tag] = klass.name
     @dump_tags[klass] = tag
   end