RFC ipv6: 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.

Jon

Jonathan T. Leighton (2):
ipv6: Inhibit IPv4-mapped src address on the wire.
ipv6: Handle IPv4-mapped src to in6addr_any dst.

 net/ipv6/datagram.c   | 14 +++++++++-----
 net/ipv6/ip6_output.c |  3 +++
 net/ipv6/tcp_ipv6.c   | 11 ++++++++---
 net/ipv6/udp.c        |  4 ++++
 4 files changed, 24 insertions(+), 8 deletions(-)

2.7.4