udp: fix early demux for mcast packets

Currently the early demux callbacks do not perform source address validation. This is not an issue for TCP or UDP unicast, where the early demux is only allowed for connected sockets and the source address is validated for the first packet and never change.

The UDP protocol currently allows early demux also for unconnected multicast sockets, and we are not currently doing any validation for them, after that the first packet lands on the socket: beyond ignoring the rp_filter - if enabled - any kind of martian sources are also allowed.

This series addresses the issue allowing the early demux callback to return an error code, and performing the proper checks for unconnected UDP multicast sockets before leveraging the rx dst cache.

Alternatively we could disable the early demux for unconnected mcast sockets, but that would cause relevant performance regression - around 50% - while with this series, with full rp_filter in place, we keep the regression to a more moderate level.

Paolo Abeni (2):
IPv4: early demux can return an error code
udp: perform source validation for mcast early demux

 include/net/protocol.h |  4 ++--
 include/net/route.h    |  4 +++-
 include/net/tcp.h      |  2 +-
 include/net/udp.h      |  2 +-
 net/ipv4/ip_input.c    | 25 +++++++++++++++----------
 net/ipv4/route.c       | 46 ++++++++++++++++++++++++++--------------------
 net/ipv4/tcp_ipv4.c    |  9 +++++----
 net/ipv4/udp.c         | 24 ++++++++++++++++++------
 8 files changed, 71 insertions(+), 45 deletions(-)

2.13.5