[syslinux] Bug#793921: tftpd-hpa: IPv6 address cannonization breaks IPv4

[Jason Gunthorpe]

On Wed, Jul 29, 2015 at 05:34:00PM +0930, Ron wrote:
> > This commit:
> > 
> >  tftp: convert IPv6-mapped IPv4 addresses to IPv4
> > 
> >  If we receive IPv4 addresses mapped to IPv6, convert them back to IPv4
> >  so that mapping scripts which use \i behave sanely.
> > 
> >  Signed-off-by: H. Peter Anvin <hpa at zytor.com>
> > 
> > Totally breaks IPv4 support when tftpd is used with an IPv6 listening socket
> > (eg when invoked from systemd)

> I think I can see a couple of ways this might start to wind down a
> rathole of workaround upon workaround for various network
> configurations

I haven't seen a followup from HPA, so I wanted to quickly comment on
this point..

> (like if the machine is only listening on an IPv6 socket, will local
> policy even allow it to send from an IPv4 one etc.)

IPv4 running in a IPv6 socket is indistinguishable at the
policy/firewall/etc level from proper IPv4, there should be no
downside to receiving a connect on a IPv6 listening socket and then
switching to an IPv4 socket for further communication.

> It's also not clear to me that croaking with an assert is the ideal
> response here, but logging a warning at least would definitely be
> helpful.

That can be changed. However, if the assert triggers it indicates a
logic flaw of some kind in the normalization code.

Jason