linux-kernel - Re: [PATCH] udp6: fix UDP/IPv6 encap resubmit path

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Date:	Mon, 7 Mar 2016 13:27:00 -0600
From:	Josh Hunt <johunt@...mai.com>
To:	Bill Sommerfeld <wsommerfeld@...gle.com>,
	"David S. Miller" <davem@...emloft.net>
Cc:	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] udp6: fix UDP/IPv6 encap resubmit path

On 03/04/2016 04:47 PM, Bill Sommerfeld wrote:
> IPv4 interprets a negative return value from a protocol handler as a
> request to redispatch to a new protocol.  In contrast, IPv6 interprets a
> negative value as an error, and interprets a positive value as a request
> for redispatch.
>
> UDP for IPv6 was unaware of this difference.  Change __udp6_lib_rcv() to
> return a positive value for redispatch.  Note that the socket's
> encap_rcv hook still needs to return a negative value to request
> dispatch, and in the case of IPv6 packets, adjust IP6CB(skb)->nhoff to
> identify the byte containing the next protocol.
>
> Signed-off-by: Bill Sommerfeld <wsommerfeld@...gle.com>
> ---
>   net/ipv6/udp.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> index 0711f8f..fd25e44 100644
> --- a/net/ipv6/udp.c
> +++ b/net/ipv6/udp.c
> @@ -922,11 +922,9 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
>   		ret = udpv6_queue_rcv_skb(sk, skb);
>   		sock_put(sk);
>
> -		/* a return value > 0 means to resubmit the input, but
> -		 * it wants the return to be -protocol, or 0
> -		 */
> +		/* a return value > 0 means to resubmit the input */
>   		if (ret > 0)
> -			return -ret;
> +			return ret;
>
>   		return 0;
>   	}
>

This looks good to me. Thanks Bill!

Josh