avoid validating file-based datastore options on assignment

file:/ strings are special with some datastore options, causing them to read a
file rather than emitting the exact string. This causes a couple of problems.

1. the valid? check needs to be special on assignment, since normalization
   really means normalizing the path, not playing with the value as we would do
   for other types

2. there are races or simply out-of-order assignments when running commands
   like 'services -p 80 -R', where the datastore option is assigned before the
   file is actually written.

This is the 'easy' fix of disabling assignment validation (which we didn't have
before anyway) for types that can expect a file:/ prefix.

lib/msf/core/data_store.rb

@@ -29,10 +29,12 @@ class DataStore < Hash
 
     opt = @options[k]
     unless opt.nil?
-      unless opt.valid?(v)
-        raise OptionValidateError.new(["Value '#{v}' is not valid for option '#{k}'#{['', ', try harder'].sample}"])
+      if opt.validate_on_assignment?
+        unless opt.valid?(v)
+          raise OptionValidateError.new(["Value '#{v}' is not valid for option '#{k}'"])
+        end
+        v = opt.normalize(v)
       end
-      v = opt.normalize(v)
     end
 
     super(k,v)

lib/msf/core/opt_address_range.rb

@@ -12,6 +12,10 @@ class OptAddressRange < OptBase
     return 'addressrange'
   end
 
+  def validate_on_assignment?
+    false
+  end
+
   def normalize(value)
     return nil unless value.kind_of?(String)
     if (value =~ /^file:(.*)/)

lib/msf/core/opt_base.rb

@@ -75,6 +75,13 @@ module Msf
       return (type == in_type)
     end
 
+    #
+    # Returns true if this option can be validated on assignment
+    #
+    def validate_on_assignment?
+      true
+    end
+
     #
     # If it's required and the value is nil or empty, then it's not valid.
     #

lib/msf/core/opt_path.rb

@@ -12,6 +12,10 @@ class OptPath < OptBase
     return 'path'
   end
 
+  def validate_on_assignment?
+    false
+  end
+
   # Generally, 'value' should be a file that exists.
   def valid?(value)
     return false if empty_required_value?(value)

lib/msf/core/opt_raw.rb

@@ -12,6 +12,10 @@ class OptRaw < OptBase
     return 'raw'
   end
 
+  def validate_on_assignment?
+    false
+  end
+
   def normalize(value)
     if (value.to_s =~ /^file:(.*)/)
       path = $1

lib/msf/core/opt_string.rb

@@ -12,6 +12,10 @@ class OptString < OptBase
     return 'string'
   end
 
+  def validate_on_assignment?
+    false
+  end
+
   def normalize(value)
     if (value.to_s =~ /^file:(.*)/)
       path = $1