netdev - Re: [PATCH net] udp: rehash on disconnect

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Message-ID: <8298ddb4-336f-d1ee-d535-21770a3a1bb6@gmail.com>
Date:   Wed, 19 Feb 2020 11:53:09 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, plroskin@...il.com, edumazet@...gle.com,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] udp: rehash on disconnect



On 2/19/20 11:16 AM, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> As of the below commit, udp sockets bound to a specific address can
> coexist with one bound to the any addr for the same port.
> 
> The commit also phased out the use of socket hashing based only on
> port (hslot), in favor of always hashing on {addr, port} (hslot2).
> 
> The change broke the following behavior with disconnect (AF_UNSPEC):
> 
>     server binds to 0.0.0.0:1337
>     server connects to 127.0.0.1:80
>     server disconnects
>     client connects to 127.0.0.1:1337
>     client sends "hello"
>     server reads "hello"	// times out, packet did not find sk
> 
> On connect the server acquires a specific source addr suitable for
> routing to its destination. On disconnect it reverts to the any addr.
> 
> The connect call triggers a rehash to a different hslot2. On
> disconnect, add the same to return to the original hslot2.
> 
> Skip this step if the socket is going to be unhashed completely.
> 
> Fixes: 4cdeeee9252a ("net: udp: prefer listeners bound to an address")
> Reported-by: Pavel Roskin <plroskin@...il.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> ---
>  net/ipv4/udp.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index db76b96092991..08a41f1e1cd22 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1857,8 +1857,12 @@ int __udp_disconnect(struct sock *sk, int flags)
>  	inet->inet_dport = 0;
>  	sock_rps_reset_rxhash(sk);
>  	sk->sk_bound_dev_if = 0;
> -	if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
> +	if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK)) {
>  		inet_reset_saddr(sk);
> +		if (sk->sk_prot->rehash &&
> +		    (sk->sk_userlocks & SOCK_BINDPORT_LOCK))
> +			sk->sk_prot->rehash(sk);
> +	}
>  
>  	if (!(sk->sk_userlocks & SOCK_BINDPORT_LOCK)) {
>  		sk->sk_prot->unhash(sk);
> 

Reviewed-by: Eric Dumazet <edumazet@...gle.com>