Consider IPv4-mapped IPv6 addresses private if IPv4 address is private

Fixes [Bug #19479]

Author: jeremyevans

lib/ipaddr.rb

@@ -263,15 +263,21 @@ def loopback?
   # Returns true if the ipaddr is a private address.  IPv4 addresses
   # in 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 as defined in RFC
   # 1918 and IPv6 Unique Local Addresses in fc00::/7 as defined in RFC
-  # 4193 are considered private.
+  # 4193 are considered private. Private IPv4 addresses in the
+  # IPv4-mapped IPv6 address range are also considered private.
   def private?
     case @family
     when Socket::AF_INET
       @addr & 0xff000000 == 0x0a000000 ||    # 10.0.0.0/8
         @addr & 0xfff00000 == 0xac100000 ||  # 172.16.0.0/12
         @addr & 0xffff0000 == 0xc0a80000     # 192.168.0.0/16
     when Socket::AF_INET6
-      @addr & 0xfe00_0000_0000_0000_0000_0000_0000_0000 == 0xfc00_0000_0000_0000_0000_0000_0000_0000
+      @addr & 0xfe00_0000_0000_0000_0000_0000_0000_0000 == 0xfc00_0000_0000_0000_0000_0000_0000_0000 ||
+        (@addr & 0xffff_0000_0000 == 0xffff_0000_0000 && (
+          @addr & 0xff000000 == 0x0a000000 ||  # ::ffff:10.0.0.0/8
+          @addr & 0xfff00000 == 0xac100000 ||  # ::ffff::172.16.0.0/12
+          @addr & 0xffff0000 == 0xc0a80000     # ::ffff::192.168.0.0/16
+        ))
     else
       raise AddressFamilyError, "unsupported address family"
     end

test/test_ipaddr.rb

@@ -426,6 +426,26 @@ def test_private?
     assert_equal(true,  IPAddr.new('fc84:8bf7:e905::1').private?)
     assert_equal(true,  IPAddr.new('fd84:8bf7:e905::1').private?)
     assert_equal(false, IPAddr.new('fe84:8bf7:e905::1').private?)
+
+    assert_equal(false, IPAddr.new('::ffff:0.0.0.0').private?)
+    assert_equal(false, IPAddr.new('::ffff:127.0.0.1').private?)
+
+    assert_equal(false, IPAddr.new('::ffff:8.8.8.8').private?)
+    assert_equal(true,  IPAddr.new('::ffff:10.0.0.0').private?)
+    assert_equal(true,  IPAddr.new('::ffff:10.255.255.255').private?)
+    assert_equal(false, IPAddr.new('::ffff:11.255.1.1').private?)
+
+    assert_equal(false, IPAddr.new('::ffff:172.15.255.255').private?)
+    assert_equal(true,  IPAddr.new('::ffff:172.16.0.0').private?)
+    assert_equal(true,  IPAddr.new('::ffff:172.31.255.255').private?)
+    assert_equal(false, IPAddr.new('::ffff:172.32.0.0').private?)
+
+    assert_equal(false, IPAddr.new('::ffff:190.168.0.0').private?)
+    assert_equal(true,  IPAddr.new('::ffff:192.168.0.0').private?)
+    assert_equal(true,  IPAddr.new('::ffff:192.168.255.255').private?)
+    assert_equal(false, IPAddr.new('::ffff:192.169.0.0').private?)
+
+    assert_equal(false, IPAddr.new('::ffff:169.254.0.1').private?)
   end
 
   def test_link_local?