Date:   Thu, 27 Oct 2016 19:56:33 -0700
From:   Tom Herbert <tom@...bertland.com>
To:     David Lebrun <david.lebrun@...ouvain.be>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 3/9] ipv6: sr: add support for SRH encapsulation and
 injection with lwtunnels

On Wed, Oct 26, 2016 at 8:54 AM, David Lebrun <david.lebrun@...ouvain.be> wrote:
> This patch creates a new type of interfaceless lightweight tunnel (SEG6),
> enabling the encapsulation and injection of SRH within locally emitted
> packets and forwarded packets.
>
> From a configuration viewpoint, a seg6 tunnel would be configured as follows:
>
>   ip -6 ro ad fc00::1/128 encap seg6 mode encap segs fc42::1,fc42::2,fc42::3 dev eth0
>
> Any packet whose destination address is fc00::1 would thus be encapsulated
> within an outer IPv6 header containing the SRH with three segments, and would
> actually be routed to the first segment of the list. If `mode inline' was
> specified instead of `mode encap', then the SRH would be directly inserted
> after the IPv6 header without outer encapsulation.
>
> Signed-off-by: David Lebrun <david.lebrun@...ouvain.be>
> ---
>  include/linux/seg6_iptunnel.h      |   6 +
>  include/net/seg6.h                 |   1 +
>  include/uapi/linux/lwtunnel.h      |   1 +
>  include/uapi/linux/seg6_iptunnel.h |  41 ++++
>  net/core/lwtunnel.c                |   2 +
>  net/ipv6/Makefile                  |   2 +-
>  net/ipv6/seg6_iptunnel.c           | 370 +++++++++++++++++++++++++++++++++++++
>  7 files changed, 422 insertions(+), 1 deletion(-)
>  create mode 100644 include/linux/seg6_iptunnel.h
>  create mode 100644 include/uapi/linux/seg6_iptunnel.h
>  create mode 100644 net/ipv6/seg6_iptunnel.c
>
> diff --git a/include/linux/seg6_iptunnel.h b/include/linux/seg6_iptunnel.h
> new file mode 100644
> index 0000000..5377cf6
> --- /dev/null
> +++ b/include/linux/seg6_iptunnel.h
> @@ -0,0 +1,6 @@
> +#ifndef _LINUX_SEG6_IPTUNNEL_H
> +#define _LINUX_SEG6_IPTUNNEL_H
> +
> +#include <uapi/linux/seg6_iptunnel.h>
> +
> +#endif
> diff --git a/include/net/seg6.h b/include/net/seg6.h
> index a9d9a9b..53d3bdb 100644
> --- a/include/net/seg6.h
> +++ b/include/net/seg6.h
> @@ -16,6 +16,7 @@
>
>  #include <linux/net.h>
>  #include <linux/ipv6.h>
> +#include <net/lwtunnel.h>
>
>  struct seg6_pernet_data {
>         struct mutex lock;
> diff --git a/include/uapi/linux/lwtunnel.h b/include/uapi/linux/lwtunnel.h
> index a478fe8..453cc62 100644
> --- a/include/uapi/linux/lwtunnel.h
> +++ b/include/uapi/linux/lwtunnel.h
> @@ -9,6 +9,7 @@ enum lwtunnel_encap_types {
>         LWTUNNEL_ENCAP_IP,
>         LWTUNNEL_ENCAP_ILA,
>         LWTUNNEL_ENCAP_IP6,
> +       LWTUNNEL_ENCAP_SEG6,
>         __LWTUNNEL_ENCAP_MAX,
>  };
>
> diff --git a/include/uapi/linux/seg6_iptunnel.h b/include/uapi/linux/seg6_iptunnel.h
> new file mode 100644
> index 0000000..da5524a
> --- /dev/null
> +++ b/include/uapi/linux/seg6_iptunnel.h
> @@ -0,0 +1,41 @@
> +/*
> + *  SR-IPv6 implementation
> + *
> + *  Author:
> + *  David Lebrun <david.lebrun@...ouvain.be>
> + *
> + *
> + *  This program is free software; you can redistribute it and/or
> + *      modify it under the terms of the GNU General Public License
> + *      as published by the Free Software Foundation; either version
> + *      2 of the License, or (at your option) any later version.
> + */
> +
> +#ifndef _UAPI_LINUX_SEG6_IPTUNNEL_H
> +#define _UAPI_LINUX_SEG6_IPTUNNEL_H
> +
> +enum {
> +       SEG6_IPTUNNEL_UNSPEC,
> +       SEG6_IPTUNNEL_SRH,
> +       __SEG6_IPTUNNEL_MAX,
> +};
> +#define SEG6_IPTUNNEL_MAX (__SEG6_IPTUNNEL_MAX - 1)
> +
> +struct seg6_iptunnel_encap {
> +       int flags;
> +       struct ipv6_sr_hdr srh[0];
> +};
> +
> +#define SEG6_IPTUN_ENCAP_SIZE(x) ((sizeof(*x)) + (((x)->srh->hdrlen + 1) << 3))
> +
> +#define SEG6_IPTUN_FLAG_ENCAP   0x1
> +
> +static inline size_t seg6_lwt_headroom(struct seg6_iptunnel_encap *tuninfo)
> +{
> +       int encap = !!(tuninfo->flags & SEG6_IPTUN_FLAG_ENCAP);
> +
> +       return ((tuninfo->srh->hdrlen + 1) << 3) +
> +              (encap * sizeof(struct ipv6hdr));
> +}
> +
> +#endif
> diff --git a/net/core/lwtunnel.c b/net/core/lwtunnel.c
> index 88fd642..03976e9 100644
> --- a/net/core/lwtunnel.c
> +++ b/net/core/lwtunnel.c
> @@ -39,6 +39,8 @@ static const char *lwtunnel_encap_str(enum lwtunnel_encap_types encap_type)
>                 return "MPLS";
>         case LWTUNNEL_ENCAP_ILA:
>                 return "ILA";
> +       case LWTUNNEL_ENCAP_SEG6:
> +               return "SEG6";
>         case LWTUNNEL_ENCAP_IP6:
>         case LWTUNNEL_ENCAP_IP:
>         case LWTUNNEL_ENCAP_NONE:
> diff --git a/net/ipv6/Makefile b/net/ipv6/Makefile
> index 29a77d3..4bd1e73 100644
> --- a/net/ipv6/Makefile
> +++ b/net/ipv6/Makefile
> @@ -45,7 +45,7 @@ obj-$(CONFIG_IPV6_TUNNEL) += ip6_tunnel.o
>  obj-$(CONFIG_IPV6_GRE) += ip6_gre.o
>  obj-$(CONFIG_IPV6_FOU) += fou6.o
>
> -obj-y += addrconf_core.o exthdrs_core.o ip6_checksum.o ip6_icmp.o seg6.o
> +obj-y += addrconf_core.o exthdrs_core.o ip6_checksum.o ip6_icmp.o seg6.o seg6_iptunnel.o
>  obj-$(CONFIG_INET) += output_core.o protocol.o $(ipv6-offload)
>
>  obj-$(subst m,y,$(CONFIG_IPV6)) += inet6_hashtables.o
> diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
> new file mode 100644
> index 0000000..caae8ab
> --- /dev/null
> +++ b/net/ipv6/seg6_iptunnel.c
> @@ -0,0 +1,370 @@
> +/*
> + *  SR-IPv6 implementation
> + *
> + *  Author:
> + *  David Lebrun <david.lebrun@...ouvain.be>
> + *
> + *
> + *  This program is free software; you can redistribute it and/or
> + *        modify it under the terms of the GNU General Public License
> + *        as published by the Free Software Foundation; either version
> + *        2 of the License, or (at your option) any later version.
> + */
> +
> +#include <linux/types.h>
> +#include <linux/skbuff.h>
> +#include <linux/net.h>
> +#include <linux/module.h>
> +#include <net/ip.h>
> +#include <net/lwtunnel.h>
> +#include <net/netevent.h>
> +#include <net/netns/generic.h>
> +#include <net/ip6_fib.h>
> +#include <net/route.h>
> +#include <net/seg6.h>
> +#include <linux/seg6.h>
> +#include <linux/seg6_iptunnel.h>
> +#include <net/addrconf.h>
> +#include <net/ip6_route.h>
> +#include <net/dst_cache.h>
> +
> +struct seg6_lwt {
> +       struct dst_cache cache;
> +       struct seg6_iptunnel_encap tuninfo[0];
> +};
> +
> +static inline struct seg6_lwt *seg6_lwt_lwtunnel(struct lwtunnel_state *lwt)
> +{
> +       return (struct seg6_lwt *)lwt->data;
> +}
> +
> +static inline struct seg6_iptunnel_encap *
> +seg6_encap_lwtunnel(struct lwtunnel_state *lwt)
> +{
> +       return seg6_lwt_lwtunnel(lwt)->tuninfo;
> +}
> +
> +static const struct nla_policy seg6_iptunnel_policy[SEG6_IPTUNNEL_MAX + 1] = {
> +       [SEG6_IPTUNNEL_SRH]     = { .type = NLA_BINARY },
> +};
> +
> +int nla_put_srh(struct sk_buff *skb, int attrtype,
> +               struct seg6_iptunnel_encap *tuninfo)
> +{
> +       struct seg6_iptunnel_encap *data;
> +       struct nlattr *nla;
> +       int len;
> +
> +       len = SEG6_IPTUN_ENCAP_SIZE(tuninfo);
> +
> +       nla = nla_reserve(skb, attrtype, len);
> +       if (!nla)
> +               return -EMSGSIZE;
> +
> +       data = nla_data(nla);
> +       memcpy(data, tuninfo, len);
> +
> +       return 0;
> +}
> +
> +static void set_tun_src(struct net *net, struct net_device *dev,
> +                       struct in6_addr *daddr, struct in6_addr *saddr)
> +{
> +       struct seg6_pernet_data *sdata = seg6_pernet(net);
> +       struct in6_addr *tun_src;
> +
> +       rcu_read_lock();
> +
> +       tun_src = rcu_dereference(sdata->tun_src);
> +
> +       if (!ipv6_addr_any(tun_src)) {
> +               memcpy(saddr, tun_src, sizeof(struct in6_addr));
> +       } else {
> +               ipv6_dev_get_saddr(net, dev, daddr, IPV6_PREFER_SRC_PUBLIC,
> +                                  saddr);
> +       }
> +
> +       rcu_read_unlock();
> +}
> +
> +/* encapsulate an IPv6 packet within an outer IPv6 header with a given SRH */
> +static int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
> +{
> +       struct net *net = dev_net(skb_dst(skb)->dev);
> +       struct ipv6hdr *hdr, *inner_hdr;
> +       struct ipv6_sr_hdr *isrh;
> +       int hdrlen, tot_len, err;
> +
> +       hdrlen = (osrh->hdrlen + 1) << 3;
> +       tot_len = hdrlen + sizeof(*hdr);
> +
> +       err = pskb_expand_head(skb, tot_len, 0, GFP_ATOMIC);
> +       if (unlikely(err))
> +               return err;
> +
> +       inner_hdr = ipv6_hdr(skb);
> +
> +       skb_push(skb, tot_len);
> +       skb_reset_network_header(skb);
> +       skb_mac_header_rebuild(skb);
> +       hdr = ipv6_hdr(skb);
> +
> +       /* inherit tc, flowlabel and hlim
> +        * hlim will be decremented in ip6_forward() afterwards and
> +        * decapsulation will overwrite inner hlim with outer hlim
> +        */
> +       ip6_flow_hdr(hdr, ip6_tclass(ip6_flowinfo(inner_hdr)),
> +                    ip6_flowlabel(inner_hdr));
> +       hdr->hop_limit = inner_hdr->hop_limit;
> +       hdr->nexthdr = NEXTHDR_ROUTING;
> +
> +       isrh = (void *)hdr + sizeof(*hdr);
> +       memcpy(isrh, osrh, hdrlen);
> +
> +       isrh->nexthdr = NEXTHDR_IPV6;
> +
> +       hdr->daddr = isrh->segments[isrh->first_segment];
> +       set_tun_src(net, skb->dev, &hdr->daddr, &hdr->saddr);
> +
> +       skb_postpush_rcsum(skb, hdr, tot_len);
> +
> +       return 0;
> +}
> +
> +/* insert an SRH within an IPv6 packet, just after the IPv6 header */
> +static int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
> +{
> +       struct ipv6hdr *hdr, *oldhdr;
> +       struct ipv6_sr_hdr *isrh;
> +       int hdrlen, err;
> +
> +       hdrlen = (osrh->hdrlen + 1) << 3;
> +
> +       err = pskb_expand_head(skb, hdrlen, 0, GFP_ATOMIC);
> +       if (unlikely(err))
> +               return err;
> +
> +       oldhdr = ipv6_hdr(skb);
> +
> +       skb_pull(skb, sizeof(struct ipv6hdr));
> +       skb_postpull_rcsum(skb, skb_network_header(skb),
> +                          sizeof(struct ipv6hdr));
> +
> +       skb_push(skb, sizeof(struct ipv6hdr) + hdrlen);
> +       skb_reset_network_header(skb);
> +       skb_mac_header_rebuild(skb);
> +
> +       hdr = ipv6_hdr(skb);
> +
> +       memmove(hdr, oldhdr, sizeof(*hdr));
> +
> +       isrh = (void *)hdr + sizeof(*hdr);
> +       memcpy(isrh, osrh, hdrlen);
> +
> +       isrh->nexthdr = hdr->nexthdr;
> +       hdr->nexthdr = NEXTHDR_ROUTING;
> +
> +       isrh->segments[0] = hdr->daddr;
> +       hdr->daddr = isrh->segments[isrh->first_segment];
> +
> +       skb_postpush_rcsum(skb, hdr, sizeof(struct ipv6hdr) + hdrlen);
> +
> +       return 0;
> +}
> +
> +static int seg6_do_srh(struct sk_buff *skb)
> +{
> +       struct dst_entry *dst = skb_dst(skb);
> +       struct seg6_iptunnel_encap *tinfo;
> +       int err = 0;
> +
> +       tinfo = seg6_encap_lwtunnel(dst->lwtstate);
> +
> +       if (likely(!skb->encapsulation)) {
> +               skb_reset_inner_headers(skb);
> +               skb->encapsulation = 1;
> +       }
> +
> +       if (tinfo->flags & SEG6_IPTUN_FLAG_ENCAP) {
> +               err = seg6_do_srh_encap(skb, tinfo->srh);
> +       } else {
> +               err = seg6_do_srh_inline(skb, tinfo->srh);
> +               skb_reset_inner_headers(skb);
> +       }
> +
> +       if (err)
> +               return err;
> +
> +       ipv6_hdr(skb)->payload_len = htons(skb->len - sizeof(struct ipv6hdr));
> +       skb_set_transport_header(skb, sizeof(struct ipv6hdr));
> +
> +       skb_set_inner_protocol(skb, skb->protocol);
> +
> +       return 0;
> +}
> +
> +int seg6_input(struct sk_buff *skb)
> +{
> +       int err;
> +
> +       err = seg6_do_srh(skb);
> +       if (unlikely(err)) {
> +               kfree_skb(skb);
> +               return err;
> +       }
> +
> +       skb_dst_drop(skb);
> +       ip6_route_input(skb);
> +
> +       return dst_input(skb);
> +}
> +
> +int seg6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
> +{
> +       struct dst_entry *orig_dst = skb_dst(skb);
> +       struct seg6_lwt *slwt;
> +       struct dst_entry *dst;
> +       int err = -EINVAL;
> +
> +       err = seg6_do_srh(skb);
> +       if (unlikely(err))
> +               goto drop;
> +
> +       slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);
> +
> +       dst = dst_cache_get(&slwt->cache);
> +       if (unlikely(!dst)) {
> +               struct ipv6hdr *hdr = ipv6_hdr(skb);
> +               struct flowi6 fl6;
> +
> +               fl6.daddr = hdr->daddr;
> +               fl6.saddr = hdr->saddr;
> +               fl6.flowlabel = ip6_flowinfo(hdr);
> +               fl6.flowi6_mark = skb->mark;
> +               fl6.flowi6_proto = hdr->nexthdr;
> +
> +               dst = ip6_route_output(net, NULL, &fl6);
> +               if (dst->error) {
> +                       err = dst->error;
> +                       dst_release(dst);
> +                       goto drop;
> +               }
> +
> +               dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
> +       }
> +
> +       skb_dst_drop(skb);
> +       skb_dst_set(skb, dst);
> +
> +       return dst_output(net, sk, skb);
> +drop:
> +       kfree_skb(skb);
> +       return err;
> +}
> +
> +static int seg6_build_state(struct net_device *dev, struct nlattr *nla,
> +                           unsigned int family, const void *cfg,
> +                           struct lwtunnel_state **ts)
> +{
> +       struct nlattr *tb[SEG6_IPTUNNEL_MAX + 1];
> +       struct seg6_iptunnel_encap *tuninfo;
> +       struct lwtunnel_state *newts;
> +       struct seg6_lwt *slwt;
> +       int tuninfo_len;
> +       int err;
> +
> +       err = nla_parse_nested(tb, SEG6_IPTUNNEL_MAX, nla,
> +                              seg6_iptunnel_policy);
> +
> +       if (err < 0)
> +               return err;
> +
> +       if (!tb[SEG6_IPTUNNEL_SRH])
> +               return -EINVAL;
> +
> +       tuninfo = nla_data(tb[SEG6_IPTUNNEL_SRH]);
> +       tuninfo_len = SEG6_IPTUN_ENCAP_SIZE(tuninfo);
> +
> +       newts = lwtunnel_state_alloc(tuninfo_len + sizeof(*slwt));
> +       if (!newts)
> +               return -ENOMEM;
> +
> +       slwt = seg6_lwt_lwtunnel(newts);
> +
> +       err = dst_cache_init(&slwt->cache, GFP_KERNEL);
> +       if (err) {
> +               kfree(newts);
> +               return err;
> +       }
> +
> +       memcpy(&slwt->tuninfo, tuninfo, tuninfo_len);
> +
> +       newts->type = LWTUNNEL_ENCAP_SEG6;
> +       newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT |
> +                       LWTUNNEL_STATE_INPUT_REDIRECT;
> +       newts->headroom = seg6_lwt_headroom(tuninfo);
> +
> +       *ts = newts;
> +
> +       return 0;
> +}
> +
> +static void seg6_destroy_state(struct lwtunnel_state *lwt)
> +{
> +       dst_cache_destroy(&seg6_lwt_lwtunnel(lwt)->cache);
> +}
> +
> +static int seg6_fill_encap_info(struct sk_buff *skb,
> +                               struct lwtunnel_state *lwtstate)
> +{
> +       struct seg6_iptunnel_encap *tuninfo = seg6_encap_lwtunnel(lwtstate);
> +
> +       if (nla_put_srh(skb, SEG6_IPTUNNEL_SRH, tuninfo))
> +               return -EMSGSIZE;
> +
> +       return 0;
> +}
> +
> +static int seg6_encap_nlsize(struct lwtunnel_state *lwtstate)
> +{
> +       struct seg6_iptunnel_encap *tuninfo = seg6_encap_lwtunnel(lwtstate);
> +
> +       return nla_total_size(SEG6_IPTUN_ENCAP_SIZE(tuninfo));
> +}
> +
> +static int seg6_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
> +{
> +       struct seg6_iptunnel_encap *a_hdr = seg6_encap_lwtunnel(a);
> +       struct seg6_iptunnel_encap *b_hdr = seg6_encap_lwtunnel(b);
> +       int len = SEG6_IPTUN_ENCAP_SIZE(a_hdr);
> +
> +       if (len != SEG6_IPTUN_ENCAP_SIZE(b_hdr))
> +               return 1;
> +
> +       return memcmp(a_hdr, b_hdr, len);
> +}
> +
> +static const struct lwtunnel_encap_ops seg6_iptun_ops = {
> +       .build_state = seg6_build_state,
> +       .destroy_state = seg6_destroy_state,
> +       .output = seg6_output,
> +       .input = seg6_input,
> +       .fill_encap = seg6_fill_encap_info,
> +       .get_encap_size = seg6_encap_nlsize,
> +       .cmp_encap = seg6_encap_cmp,
> +};
> +
> +static int __init seg6_iptunnel_init(void)
> +{
> +       return lwtunnel_encap_add_ops(&seg6_iptun_ops, LWTUNNEL_ENCAP_SEG6);
> +}
> +module_init(seg6_iptunnel_init);
> +
> +static void __exit seg6_iptunnel_exit(void)
> +{
> +       lwtunnel_encap_del_ops(&seg6_iptun_ops, LWTUNNEL_ENCAP_SEG6);
> +}
> +module_exit(seg6_iptunnel_exit);
> +
> +MODULE_DESCRIPTION("Segment Routing with IPv6 IP Tunnels");
> +MODULE_LICENSE("GPL v2");
> --
> 2.7.3
>

Looks good.

Acked-by: Tom Herbert <tom@...bertland.com>

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