Fix mapping invalid non-file object.

io_buffer.c

@@ -322,6 +322,9 @@ io_buffer_map(int argc, VALUE *argv, VALUE klass)
     }
 
     VALUE io = argv[0];
+    if (!RB_TYPE_P(io, T_FILE)) {
+        rb_raise(rb_eArgError, "Must be file/io!");
+    }
 
     size_t size;
     if (argc >= 2) {

test/ruby/test_io_buffer.rb

@@ -9,10 +9,6 @@ class TestIOBuffer < Test::Unit::TestCase
     Warning[:experimental] = experimental
   end
 
-  def test_default_size
-    assert_equal IO::Buffer::DEFAULT_SIZE, IO::Buffer.new.size
-  end
-
   def assert_negative(value)
     assert(value < 0, "Expected #{value} to be negative!")
   end
@@ -40,6 +36,10 @@ class TestIOBuffer < Test::Unit::TestCase
     assert_include [IO::Buffer::LITTLE_ENDIAN, IO::Buffer::BIG_ENDIAN], IO::Buffer::HOST_ENDIAN
   end
 
+  def test_default_size
+    assert_equal IO::Buffer::DEFAULT_SIZE, IO::Buffer.new.size
+  end
+
   def test_new_internal
     buffer = IO::Buffer.new(1024, IO::Buffer::INTERNAL)
     assert_equal 1024, buffer.size
@@ -74,6 +74,12 @@ class TestIOBuffer < Test::Unit::TestCase
     assert_include buffer.to_str, "Hello World"
   end
 
+  def test_file_mapped_invalid
+    assert_raise ArgumentError do
+      IO::Buffer.map("foobar")
+    end
+  end
+
   def test_string_mapped
     string = "Hello World"
     buffer = IO::Buffer.for(string)