Subject: Re: [PATCH] udp: add rehash on connect()

From: Krzysztof Olędzki <[email-masked]>
Date: Wed, 08 Sep 2010 17:06:29 +0200

On 2010-09-08 12:10, Eric Dumazet wrote:
> 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 <[email-masked]>
> Signed-off-by: Eric Dumazet <[email-masked]>

Thanks, I'll test this patch this evening.

Best regards,

			Krzysztof Olędzki