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
