[BUG] Inet6Address.isIPv4CompatibleAddress uses wrong prefix

[Langer, Christoph]

Hi Rob,

sending this over to net-dev, where it should be discussed...

/Christoph

> -----Original Message-----
> From: core-libs-dev <core-libs-dev-bounces at openjdk.java.net> On Behalf
> Of Rob Spoor
> Sent: Montag, 24. Juni 2019 22:58
> To: core-libs-dev at openjdk.java.net
> Subject: [BUG] Inet6Address.isIPv4CompatibleAddress uses wrong prefix
> 
> I found a bug in Inet6Adress.isIPv4CompatibleAddress(). While parsing
> correctly uses the ::ffff:<IPv4> format, isIPv4CompatibleAddress()
> checks for ::<IPv4> instead. An example:
> 
>      Inet6Address address = (Inet6Address)
> InetAddress.getByName("::192.168.1.13");
>      System.out.printf("%s: %b%n", address,
> address.isIPv4CompatibleAddress());
> 
> This should print false, but instead it prints true.
> 
> The error is in the Inet6Address.Inet6AddressHolder class:
> 
>          boolean isIPv4CompatibleAddress() {
>              if ((ipaddress[0] == 0x00) && (ipaddress[1] == 0x00) &&
>                  (ipaddress[2] == 0x00) && (ipaddress[3] == 0x00) &&
>                  (ipaddress[4] == 0x00) && (ipaddress[5] == 0x00) &&
>                  (ipaddress[6] == 0x00) && (ipaddress[7] == 0x00) &&
>                  (ipaddress[8] == 0x00) && (ipaddress[9] == 0x00) &&
>                  (ipaddress[10] == 0x00) && (ipaddress[11] == 0x00))  {
>                  return true;
>              }
>              return false;
>          }
> 
> I think that bytes 10 and 11 should both be (byte) 0xFF instead of 0x00.
> This is what's being used in IPAddressUtil, which is used for parsing:
> 
>      private static boolean isIPv4MappedAddress(byte[] addr) {
>          if (addr.length < INADDR16SZ) {
>              return false;
>          }
>          if ((addr[0] == 0x00) && (addr[1] == 0x00) &&
>              (addr[2] == 0x00) && (addr[3] == 0x00) &&
>              (addr[4] == 0x00) && (addr[5] == 0x00) &&
>              (addr[6] == 0x00) && (addr[7] == 0x00) &&
>              (addr[8] == 0x00) && (addr[9] == 0x00) &&
>              (addr[10] == (byte)0xff) &&
>              (addr[11] == (byte)0xff))  {
>              return true;
>          }
>          return false;
>      }
> 
> Maybe it's an idea to let Inet6Address.Inet6AddressHolder delegate to
> this latter method?
> 
> 
> Rob