Gregory Nutt fb8cf9373c net/udp: Resolve race condition in connection-less UDP sockets with read-ahead buffering.
In connection-mode UDP sockets, a remote address is retained in the UDP connection structure.  This determines both there send() will send the packets and which packets recv() will accept.

This same mechanism is used for connection-less UDP sendto:  A temporary remote address is written into the connection structure to support the sendto() operation.  That address persists until the next recvfrom() when it is reset to accept any address.

When UDP read-ahead buffering is enabled, however, that means that the old, invalid remote address can be left in the connection structure for some time.  This can cause read-ahead buffer to fail, dropping UDP packets.

Shortening the time between when he remote address is reset (i.e., immediately after the sendto() completes) is not a solution, that does not eliminate the race condition; in only makes it smaller.

With this change, a flag was added to the connection structure to indicate if the UDP socket is in connection mode or if it is connection-less.  This change effects only UDP receive operations:  The remote address in the UDP connection is always ignored if the UDP socket is not in connection-mode.

No for connection-mode sockets, that remote address behaves as before.  But for connection-less sockets, it is only used by sendto().
2018-05-13 09:57:34 -06:00
..
2017-09-20 10:06:26 -06:00

README
======

Directory Structure
===================

  nuttx/
   |
   `- net/
       |
       +- arp        - Address resolution protocol (IPv4)
       +- bluetooth  - PF_BLUETOOTH socket interface
       +- devif      - Stack/device interface layer
       +- icmp       - Internet Control Message Protocol (IPv4)
       +- icmpv6     - Internet Control Message Protocol (IPv6)
       +- ieee802154 - PF_IEEE802154 socket interface
       +- inet       - PF_INET/PF_INET6 socket interface
       +- ipforward  - IP forwarding logic
       +- local      - Unix domain (local) sockets
       +- loopback   - Local loopback
       +- neighbor   - Neighbor Discovery Protocol (IPv6)
       +- netdev     - Socket network device interface
       +- pkt        - "Raw" packet socket support
       +- sixlowpan  - 6LoWPAN implementation
       +- socket     - BSD socket interface
       +- route      - Routing table support
       +- tcp        - Transmission Control Protocol
       +- udp        - User Datagram Protocol
       +- usrsock    - User socket API for user-space networking stack
       `- utils      - Miscellaneous utility functions

    +-------------------------------------------------------------------++------------------------+
    |                     Application layer                             || usrsock daemon         |
    +-------------------------------------------------------------------++------------------------+
    +-------------------------------------------------------------------++----------------+ +-----+
    |                   Socket layer (socket/)                          || /dev/usrsock   | |     |
    +-------------------------------------------------------------------++----------------+ |     |
    +------------++--------------------------------------------------++-------------------+ |     |
    |  Network   || Protocol stacks (arp, ipv6, icmp, pkt, tcp, udp) || usrsock/          | |     |
    |   Device   |+--------------------------------------------------++-------------------+ |     |
    | Interface  |+------------------------------------++---------------------------------+ |     |
    | (netdev/)  ||  Network Device Interface (devif/) || Utilities                       | |     |
    +------------++------------------------------------++---------------------------------+ |     |
    +----------------------------------------------------------------+                      |     |
    |                    Network Device Drivers                      |                      | HAL |
    +----------------------------------------------------------------+                      +-----+
    +----------------------------------------------------------------+ +--------------------------+
    |                    Networking Hardware                         | |  Hardware TCP/IP Stack   |
    +----------------------------------------------------------------+ +--------------------------+