commit 749f63ed9bf702e588000f1d1ce6290e6c156289
Author: Eric Dumazet <eric.dumazet@gmail.com>
Date:   Wed Sep 8 05:08:44 2010 +0000

    udp: add rehash on connect()

    commit 719f835853a92f6090258114a72ffe41f09155cd upstream

    commit 30fff923 introduced in linux-2.6.33 (udp: bind() optimisation)
    added a secondary hash on UDP, hashed on (local addr, local port).

    Problem is that following sequence :

    fd = socket(...)
    connect(fd, &remote, ...)

    not only selects remote end point (address and port), but also sets
    local address, while UDP stack stored in secondary hash table the socket
    while its local address was INADDR_ANY (or ipv6 equivalent)

    Sequence is :
     - autobind() : choose a random local port, insert socket in hash tables
                  [while local address is INADDR_ANY]
     - connect() : set remote address and port, change local address to IP
                  given by a route lookup.

    When an incoming UDP frame comes, if more than 10 sockets are found in
    primary hash table, we switch to secondary table, and fail to find
    socket because its local address changed.

    One solution to this problem is to rehash datagram socket if needed.

    We add a new rehash(struct socket *) method in "struct proto", and
    implement this method for UDP v4 & v6, using a common helper.

    This rehashing only takes care of secondary hash table, since primary
    hash (based on local port only) is not changed.

    Reported-by: Krzysztof Piotr Oledzki <ole@ans.pl>
    Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
    Tested-by: Krzysztof Piotr Oledzki <ole@ans.pl>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>