Merge branch 'ipv6-v4mapped'

Jonathan T. Leighton says:

====================
IPv4-mapped on wire, :: dst address issue

Under some circumstances IPv6 datagrams are sent with IPv4-mapped IPv6
addresses as the source. Given an IPv6 socket bound to an IPv4-mapped
IPv6 address, and an IPv6 destination address, both TCP and UDP will
will send packets using the IPv4-mapped IPv6 address as the source. Per
RFC 6890 (Table 20), IPv4-mapped IPv6 source addresses are not allowed
in an IP datagram. The problem can be observed by attempting to
connect() either a TCP or UDP socket, or by using sendmsg() with a UDP
socket. The patch is intended to correct this issue for all socket
types.

linux follows the BSD convention that an IPv6 destination address
specified as in6addr_any is converted to the loopback address.
Currently, neither TCP nor UDP consider the possibility that the source
address is an IPv4-mapped IPv6 address, and assume that the appropriate
loopback address is ::1. The patch adds a check on whether or not the
source address is an IPv4-mapped IPv6 address and then sets the
destination address to either ::ffff:127.0.0.1 or ::1, as appropriate.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>