Subject: Re: [PATCH net-next 1/8] flow_keys: Record IP layer protocol in skb_flow_dissect()

From: Daniel Borkmann <[email-masked]>
Date: Tue, 10 Jun 2014 15:11:17 +0200

On 06/09/2014 08:32 PM, Govindarajulu Varadarajan wrote:
> skb_flow_dissect() dissects only transport header type in ip_proto. It dose not
> give any information about IPv4 or IPv6.
>
> This patch adds new member, n_proto, to struct flow_keys. Which records the
> IP layer type. i.e IPv4 or IPv6.
>
> This can be used in netdev->ndo_rx_flow_steer driver function to dissect flow.
>
> Adding new member to flow_keys increases the struct size by around 4 bytes.
> This causes BUILD_BUG_ON(sizeof(qcb->data) < sz); to fail in
> qdisc_cb_private_validate()
>
> So increase data size by 4
>
> Signed-off-by: Govindarajulu Varadarajan <[email-masked]>
> ---
>   include/net/flow_keys.h   | 14 ++++++++++++++
>   include/net/sch_generic.h |  2 +-
>   net/core/flow_dissector.c |  1 +
>   3 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/flow_keys.h b/include/net/flow_keys.h
> index 7e64bd8..fbefdca 100644
> --- a/include/net/flow_keys.h
> +++ b/include/net/flow_keys.h
> @@ -1,6 +1,19 @@
>   #ifndef _NET_FLOW_KEYS_H
>   #define _NET_FLOW_KEYS_H
>
> +/* struct flow_keys:
> + *	@src: source ip address in case of IPv4
> + *	      For IPv6 it contains 32bit hash of src address
> + *	@dst: destination ip address in case of IPv4
> + *	      For IPv6 it contains 32bit hash of dst address
> + *	@ports: port numbers of Transport header
> + *		port16[0]: src port number
> + *		port16[1]: dst port number
> + *	@thoff: Transport header offset
> + *	@n_proto: Network header protocol (eg. IPv4/IPv6)
> + *	@ip_proto: Transport header protocol (eg. TCP/UDP)
> + * All the members, except thoff, are in network byte order.
> + */
>   struct flow_keys {
>   	/* (src,dst) must be grouped, in the same way than in IP header */
>   	__be32 src;
> @@ -10,6 +23,7 @@ struct flow_keys {
>   		__be16 port16[2];
>   	};
>   	u16 thoff;
> +	u16 n_proto;
>   	u8 ip_proto;
>   };
>
> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
> index 624f985..a3cfb8e 100644
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -231,7 +231,7 @@ struct qdisc_skb_cb {
>   	unsigned int		pkt_len;
>   	u16			slave_dev_queue_mapping;
>   	u16			_pad;
> -	unsigned char		data[20];
> +	unsigned char		data[24];

I'm wondering if this is actually needed. We add an extra
u16 n_proto into the flow_keys *just* to determine IPv4/v6
while if it finds anything else than this the dissector
returns false anyway w/o filling out the flow keys structure.
Plus, in case of IPv6 you'll have a hashed/folded src/dst
addr anyway.

>   };
>
>   static inline void qdisc_cb_private_validate(const struct sk_buff *skb, int sz)
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index 107ed12..c2b53c1 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -175,6 +175,7 @@ ipv6:
>   		break;
>   	}
>
> +	flow->n_proto = proto;
>   	flow->ip_proto = ip_proto;
>   	flow->ports = skb_flow_get_ports(skb, nhoff, ip_proto);
>   	flow->thoff = (u16) nhoff;
>