Re: [nf-next] netfilter: extend SRH match to support matching previous, next and last SID

Pablo Neira Ayuso
2018-04-23T17:30:47Z

On Mon, Apr 23, 2018 at 05:48:22AM -0500, Ahmed Abdelsalam wrote:
> IPv6 Segment Routing Header (SRH) contains a list of SIDs to be crossed by
> SR encapsulated packet. Each SID is encoded as an IPv6 prefix.
>
> When a Firewall receives an SR encapsulated packet, it should be able to
> identify which node previously processed the packet (previous SID), which
> node is going to process the packet next (next SID), and which node is the
> last to process the packet (last SID) which represent the final destination
> of the packet in case of inline SR mode.
>
> An example use-case of using these features could be SID list that includes
> two firewalls. When the second firewall receives a packet, it can check
> whether the packet has been processed by the first firewall or not. Based on
> that check, it decides to apply all rules, apply just subset of the rules,
> or totally skip all rules and forward the packet to the next SID.
>
> This patch extends SRH match to support matching previous SID, next SID, and
> last SID.
>
> Signed-off-by: Ahmed Abdelsalam <amsalam20@gmail.com>
> ---
> include/uapi/linux/netfilter_ipv6/ip6t_srh.h | 22 +++++++++++++--
> net/ipv6/netfilter/ip6t_srh.c | 41 +++++++++++++++++++++++++++-
> 2 files changed, 60 insertions(+), 3 deletions(-)
>
> diff --git a/include/uapi/linux/netfilter_ipv6/ip6t_srh.h b/include/uapi/linux/netfilter_ipv6/ip6t_srh.h
> index f3cc0ef..9808382 100644
> --- a/include/uapi/linux/netfilter_ipv6/ip6t_srh.h
> +++ b/include/uapi/linux/netfilter_ipv6/ip6t_srh.h
> @@ -17,7 +17,10 @@
> #define IP6T_SRH_LAST_GT 0x0100
> #define IP6T_SRH_LAST_LT 0x0200
> #define IP6T_SRH_TAG 0x0400
> -#define IP6T_SRH_MASK 0x07FF
> +#define IP6T_SRH_PSID 0x0800
> +#define IP6T_SRH_NSID 0x1000
> +#define IP6T_SRH_LSID 0x2000
> +#define IP6T_SRH_MASK 0x3FFF
>
> /* Values for "mt_invflags" field in struct ip6t_srh */
> #define IP6T_SRH_INV_NEXTHDR 0x0001
> @@ -31,7 +34,10 @@
> #define IP6T_SRH_INV_LAST_GT 0x0100
> #define IP6T_SRH_INV_LAST_LT 0x0200
> #define IP6T_SRH_INV_TAG 0x0400
> -#define IP6T_SRH_INV_MASK 0x07FF
> +#define IP6T_SRH_INV_PSID 0x0800
> +#define IP6T_SRH_INV_NSID 0x1000
> +#define IP6T_SRH_INV_LSID 0x2000
> +#define IP6T_SRH_INV_MASK 0x3FFF
>
> /**
> * struct ip6t_srh - SRH match options
> @@ -40,6 +46,12 @@
> * @ segs_left: Segments left field of SRH
> * @ last_entry: Last entry field of SRH
> * @ tag: Tag field of SRH
> + * @ psid_addr: Address of previous SID in SRH SID list
> + * @ nsid_addr: Address of NEXT SID in SRH SID list
> + * @ lsid_addr: Address of LAST SID in SRH SID list
> + * @ psid_msk: Mask of previous SID in SRH SID list
> + * @ nsid_msk: Mask of next SID in SRH SID list
> + * @ lsid_msk: MAsk of last SID in SRH SID list
> * @ mt_flags: match options
> * @ mt_invflags: Invert the sense of match options
> */
> @@ -50,6 +62,12 @@ struct ip6t_srh {
> __u8 segs_left;
> __u8 last_entry;
> __u16 tag;
> + struct in6_addr psid_addr;
> + struct in6_addr nsid_addr;
> + struct in6_addr lsid_addr;
> + struct in6_addr psid_msk;
> + struct in6_addr nsid_msk;
> + struct in6_addr lsid_msk;

This is changing something exposed through UAPI, so you will need a
new revision for this.

> __u16 mt_flags;
> __u16 mt_invflags;
> };
> diff --git a/net/ipv6/netfilter/ip6t_srh.c b/net/ipv6/netfilter/ip6t_srh.c
> index 33719d5..2b5cc73 100644
> --- a/net/ipv6/netfilter/ip6t_srh.c
> +++ b/net/ipv6/netfilter/ip6t_srh.c
> @@ -30,7 +30,9 @@ static bool srh_mt6(const struct sk_buff *skb, struct xt_action_param *par)
> const struct ip6t_srh *srhinfo = par->matchinfo;
> struct ipv6_sr_hdr *srh;
> struct ipv6_sr_hdr _srh;
> - int hdrlen, srhoff = 0;
> + int hdrlen, psidoff, nsidoff, lsidoff, srhoff = 0;
> + struct in6_addr *psid, *nsid, *lsid;
> + struct in6_addr _psid, _nsid, _lsid;

Could you rearrange variable definitions? ie. longest line first, eg.

int hdrlen, psidoff, nsidoff, lsidoff, srhoff = 0;
const struct ip6t_srh *srhinfo = par->matchinfo;
struct in6_addr *psid, *nsid, *lsid;
struct ipv6_sr_hdr *srh;
struct ipv6_sr_hdr _srh;

Thanks.