[PATCH v2 00/16] Simplify and correct handling of "spliced" UDP forwarding

[David Gibson <david@gibson.dropbear.id.au>]

The UDP "splicing" (forwarding packets from one L4 socket to another,
rather than via the tuntap device) code assumes that any given UDP
port in the init namespace will only communicate with a single port on
the ns side at a time, and vice versa.  This will often be the case,
but since UDP is a connectionless protocol, it need not be.  In fact
it is not the case in our existing UDP bandwidth checks, although the
specific configuration there means it's not harmful in that case.

The failure mode in this case can be quite bad: we don't just fall
back to an unoptimized oath, or drop packets, we will misdirect
packets to the wrong destination.

This series make some substantial simplifications to how we handle the
splice forwarding, then corrects it to handle the case of multiple
source ports sending to a single destination.

This does come at a performance cost.  It's not as large as I feared,
and shouldn't affect the most common case where there is a 1 to 1
mapping between source and destination ports.  I haven't yet been able
to confirm the latter because the iperf3 bandwidth test we use *does*
have interleaved streams with a common destination port.

Based on the earlier series for dual stack TCP sockets.

Changes since v1:
 * Added patches 12..16/16 fixing the delivery of packets, as well as
   just simplifying the mechanics

David Gibson (16):
  udp: Also bind() connected ports for "splice" forwarding
  udp: Separate tracking of inbound and outbound packet flows
  udp: Always use sendto() rather than send() for forwarding spliced
    packets
  udp: Don't connect "forward" sockets for spliced flows
  udp: Remove the @bound field from union udp_epoll_ref
  udp: Split splice field in udp_epoll_ref into (mostly) independent
    bits
  udp: Don't create double sockets for -U port
  udp: Re-use fixed bound sockets for packet forwarding when possible
  udp: Don't explicitly track originating socket for spliced
    "connections"
  udp: Update UDP "connection" timestamps in both directions
  udp: Simplify udp_sock_handler_splice
  udp: Make UDP_SPLICE_FRAMES and UDP_TAP_FRAMES_MEM the same thing
  udp: Add helper to extract port from a sockaddr_in or sockaddr_in6
  udp: Unify buffers for tap and splice paths
  udp: Split send half of udp_sock_handler_splice() from the receive
    half
  udp: Correct splice forwarding when receiving from multiple sources

 passt.h |   2 +
 udp.c   | 518 +++++++++++++++++++++++++-------------------------------
 udp.h   |  16 +-
 3 files changed, 244 insertions(+), 292 deletions(-)

-- 
2.38.1