// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  SR-IPv6 implementation
 *
 *  Author:
 *  David Lebrun <david.lebrun@uclouvain.be>
 */

#include <linux/types.h>
#include <linux/skbuff.h>
#include <linux/net.h>
#include <linux/module.h>
#include <net/ip.h>
#include <net/ip_tunnels.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>
#ifdef CONFIG_IPV6_SEG6_HMAC
#include <net/seg6_hmac.h>
#endif
#include <linux/netfilter.h>

static size_t seg6_lwt_headroom(struct seg6_iptunnel_encap *tuninfo)
{
        int head = 0;

        switch (tuninfo->mode) {
        case SEG6_IPTUN_MODE_INLINE:
                break;
        case SEG6_IPTUN_MODE_ENCAP:
        case SEG6_IPTUN_MODE_ENCAP_RED:
                head = sizeof(struct ipv6hdr);
                break;
        case SEG6_IPTUN_MODE_L2ENCAP:
        case SEG6_IPTUN_MODE_L2ENCAP_RED:
                return 0;
        }

        return ((tuninfo->srh->hdrlen + 1) << 3) + head;
}

struct seg6_lwt {
        struct dst_cache cache;
        struct seg6_iptunnel_encap tuninfo[];
};

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 },
};

static 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();
}

/* Compute flowlabel for outer IPv6 header */
static __be32 seg6_make_flowlabel(struct net *net, struct sk_buff *skb,
                                  struct ipv6hdr *inner_hdr)
{
        int do_flowlabel = net->ipv6.sysctl.seg6_flowlabel;
        __be32 flowlabel = 0;
        u32 hash;

        if (do_flowlabel > 0) {
                hash = skb_get_hash(skb);
                hash = rol32(hash, 16);
                flowlabel = (__force __be32)hash & IPV6_FLOWLABEL_MASK;
        } else if (!do_flowlabel && skb->protocol == htons(ETH_P_IPV6)) {
                flowlabel = ip6_flowlabel(inner_hdr);
        }
        return flowlabel;
}

static int __seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
                               int proto, struct dst_entry *cache_dst)
{
        struct dst_entry *dst = skb_dst(skb);
        struct net_device *dev = dst_dev(dst);
        struct net *net = dev_net(dev);
        struct ipv6hdr *hdr, *inner_hdr;
        struct ipv6_sr_hdr *isrh;
        int hdrlen, tot_len, err;
        __be32 flowlabel;

        hdrlen = (osrh->hdrlen + 1) << 3;
        tot_len = hdrlen + sizeof(*hdr);

        err = skb_cow_head(skb, tot_len + dst_dev_overhead(cache_dst, skb));
        if (unlikely(err))
                return err;

        inner_hdr = ipv6_hdr(skb);
        flowlabel = seg6_make_flowlabel(net, skb, inner_hdr);

        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
         */

        if (skb->protocol == htons(ETH_P_IPV6)) {
                ip6_flow_hdr(hdr, ip6_tclass(ip6_flowinfo(inner_hdr)),
                             flowlabel);
                hdr->hop_limit = inner_hdr->hop_limit;
        } else {
                ip6_flow_hdr(hdr, 0, flowlabel);
                hdr->hop_limit = ip6_dst_hoplimit(skb_dst(skb));

                memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));

                /* the control block has been erased, so we have to set the
                 * iif once again.
                 * We read the receiving interface index directly from the
                 * skb->skb_iif as it is done in the IPv4 receiving path (i.e.:
                 * ip_rcv_core(...)).
                 */
                IP6CB(skb)->iif = skb->skb_iif;
        }

        hdr->nexthdr = NEXTHDR_ROUTING;

        isrh = (void *)hdr + sizeof(*hdr);
        memcpy(isrh, osrh, hdrlen);

        isrh->nexthdr = proto;

        hdr->daddr = isrh->segments[isrh->first_segment];
        set_tun_src(net, dev, &hdr->daddr, &hdr->saddr);

#ifdef CONFIG_IPV6_SEG6_HMAC
        if (sr_has_hmac(isrh)) {
                err = seg6_push_hmac(net, &hdr->saddr, isrh);
                if (unlikely(err))
                        return err;
        }
#endif

        hdr->payload_len = htons(skb->len - sizeof(struct ipv6hdr));

        skb_postpush_rcsum(skb, hdr, tot_len);

        return 0;
}

/* encapsulate an IPv6 packet within an outer IPv6 header with a given SRH */
int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
{
        return __seg6_do_srh_encap(skb, osrh, proto, NULL);
}
EXPORT_SYMBOL_GPL(seg6_do_srh_encap);

/* encapsulate an IPv6 packet within an outer IPv6 header with reduced SRH */
static int seg6_do_srh_encap_red(struct sk_buff *skb,
                                 struct ipv6_sr_hdr *osrh, int proto,
                                 struct dst_entry *cache_dst)
{
        __u8 first_seg = osrh->first_segment;
        struct dst_entry *dst = skb_dst(skb);
        struct net_device *dev = dst_dev(dst);
        struct net *net = dev_net(dev);
        struct ipv6hdr *hdr, *inner_hdr;
        int hdrlen = ipv6_optlen(osrh);
        int red_tlv_offset, tlv_offset;
        struct ipv6_sr_hdr *isrh;
        bool skip_srh = false;
        __be32 flowlabel;
        int tot_len, err;
        int red_hdrlen;
        int tlvs_len;

        if (first_seg > 0) {
                red_hdrlen = hdrlen - sizeof(struct in6_addr);
        } else {
                /* NOTE: if tag/flags and/or other TLVs are introduced in the
                 * seg6_iptunnel infrastructure, they should be considered when
                 * deciding to skip the SRH.
                 */
                skip_srh = !sr_has_hmac(osrh);

                red_hdrlen = skip_srh ? 0 : hdrlen;
        }

        tot_len = red_hdrlen + sizeof(struct ipv6hdr);

        err = skb_cow_head(skb, tot_len + dst_dev_overhead(cache_dst, skb));
        if (unlikely(err))
                return err;

        inner_hdr = ipv6_hdr(skb);
        flowlabel = seg6_make_flowlabel(net, skb, inner_hdr);

        skb_push(skb, tot_len);
        skb_reset_network_header(skb);
        skb_mac_header_rebuild(skb);
        hdr = ipv6_hdr(skb);

        /* based on seg6_do_srh_encap() */
        if (skb->protocol == htons(ETH_P_IPV6)) {
                ip6_flow_hdr(hdr, ip6_tclass(ip6_flowinfo(inner_hdr)),
                             flowlabel);
                hdr->hop_limit = inner_hdr->hop_limit;
        } else {
                ip6_flow_hdr(hdr, 0, flowlabel);
                hdr->hop_limit = ip6_dst_hoplimit(skb_dst(skb));

                memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
                IP6CB(skb)->iif = skb->skb_iif;
        }

        /* no matter if we have to skip the SRH or not, the first segment
         * always comes in the pushed IPv6 header.
         */
        hdr->daddr = osrh->segments[first_seg];

        if (skip_srh) {
                hdr->nexthdr = proto;

                set_tun_src(net, dev, &hdr->daddr, &hdr->saddr);
                goto out;
        }

        /* we cannot skip the SRH, slow path */

        hdr->nexthdr = NEXTHDR_ROUTING;
        isrh = (void *)hdr + sizeof(struct ipv6hdr);

        if (unlikely(!first_seg)) {
                /* this is a very rare case; we have only one SID but
                 * we cannot skip the SRH since we are carrying some
                 * other info.
                 */
                memcpy(isrh, osrh, hdrlen);
                goto srcaddr;
        }

        tlv_offset = sizeof(*osrh) + (first_seg + 1) * sizeof(struct in6_addr);
        red_tlv_offset = tlv_offset - sizeof(struct in6_addr);

        memcpy(isrh, osrh, red_tlv_offset);

        tlvs_len = hdrlen - tlv_offset;
        if (unlikely(tlvs_len > 0)) {
                const void *s = (const void *)osrh + tlv_offset;
                void *d = (void *)isrh + red_tlv_offset;

                memcpy(d, s, tlvs_len);
        }

        --isrh->first_segment;
        isrh->hdrlen -= 2;

srcaddr:
        isrh->nexthdr = proto;
        set_tun_src(net, dev, &hdr->daddr, &hdr->saddr);

#ifdef CONFIG_IPV6_SEG6_HMAC
        if (unlikely(!skip_srh && sr_has_hmac(isrh))) {
                err = seg6_push_hmac(net, &hdr->saddr, isrh);
                if (unlikely(err))
                        return err;
        }
#endif

out:
        hdr->payload_len = htons(skb->len - sizeof(struct ipv6hdr));

        skb_postpush_rcsum(skb, hdr, tot_len);

        return 0;
}

static int __seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
                                struct dst_entry *cache_dst)
{
        struct ipv6hdr *hdr, *oldhdr;
        struct ipv6_sr_hdr *isrh;
        int hdrlen, err;

        hdrlen = (osrh->hdrlen + 1) << 3;

        err = skb_cow_head(skb, hdrlen + dst_dev_overhead(cache_dst, skb));
        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];

#ifdef CONFIG_IPV6_SEG6_HMAC
        if (sr_has_hmac(isrh)) {
                struct net *net = skb_dst_dev_net(skb);

                err = seg6_push_hmac(net, &hdr->saddr, isrh);
                if (unlikely(err))
                        return err;
        }
#endif

        hdr->payload_len = htons(skb->len - sizeof(struct ipv6hdr));

        skb_postpush_rcsum(skb, hdr, sizeof(struct ipv6hdr) + hdrlen);

        return 0;
}

static int seg6_do_srh(struct sk_buff *skb, struct dst_entry *cache_dst)
{
        struct dst_entry *dst = skb_dst(skb);
        struct seg6_iptunnel_encap *tinfo;
        int proto, err = 0;

        tinfo = seg6_encap_lwtunnel(dst->lwtstate);

        switch (tinfo->mode) {
        case SEG6_IPTUN_MODE_INLINE:
                if (skb->protocol != htons(ETH_P_IPV6))
                        return -EINVAL;

                err = __seg6_do_srh_inline(skb, tinfo->srh, cache_dst);
                if (err)
                        return err;
                break;
        case SEG6_IPTUN_MODE_ENCAP:
        case SEG6_IPTUN_MODE_ENCAP_RED:
                err = iptunnel_handle_offloads(skb, SKB_GSO_IPXIP6);
                if (err)
                        return err;

                if (skb->protocol == htons(ETH_P_IPV6))
                        proto = IPPROTO_IPV6;
                else if (skb->protocol == htons(ETH_P_IP))
                        proto = IPPROTO_IPIP;
                else
                        return -EINVAL;

                if (tinfo->mode == SEG6_IPTUN_MODE_ENCAP)
                        err = __seg6_do_srh_encap(skb, tinfo->srh,
                                                  proto, cache_dst);
                else
                        err = seg6_do_srh_encap_red(skb, tinfo->srh,
                                                    proto, cache_dst);

                if (err)
                        return err;

                skb_set_inner_transport_header(skb, skb_transport_offset(skb));
                skb_set_inner_protocol(skb, skb->protocol);
                skb->protocol = htons(ETH_P_IPV6);
                break;
        case SEG6_IPTUN_MODE_L2ENCAP:
        case SEG6_IPTUN_MODE_L2ENCAP_RED:
                if (!skb_mac_header_was_set(skb))
                        return -EINVAL;

                if (pskb_expand_head(skb, skb->mac_len, 0, GFP_ATOMIC) < 0)
                        return -ENOMEM;

                skb_mac_header_rebuild(skb);
                skb_push(skb, skb->mac_len);

                if (tinfo->mode == SEG6_IPTUN_MODE_L2ENCAP)
                        err = __seg6_do_srh_encap(skb, tinfo->srh,
                                                  IPPROTO_ETHERNET,
                                                  cache_dst);
                else
                        err = seg6_do_srh_encap_red(skb, tinfo->srh,
                                                    IPPROTO_ETHERNET,
                                                    cache_dst);

                if (err)
                        return err;

                skb->protocol = htons(ETH_P_IPV6);
                break;
        }

        skb_set_transport_header(skb, sizeof(struct ipv6hdr));
        nf_reset_ct(skb);

        return 0;
}

/* insert an SRH within an IPv6 packet, just after the IPv6 header */
int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
{
        return __seg6_do_srh_inline(skb, osrh, NULL);
}
EXPORT_SYMBOL_GPL(seg6_do_srh_inline);

static int seg6_input_finish(struct net *net, struct sock *sk,
                             struct sk_buff *skb)
{
        return dst_input(skb);
}

static int seg6_input_core(struct net *net, struct sock *sk,
                           struct sk_buff *skb)
{
        struct dst_entry *orig_dst = skb_dst(skb);
        struct dst_entry *dst = NULL;
        struct lwtunnel_state *lwtst;
        struct seg6_lwt *slwt;
        int err;

        /* We cannot dereference "orig_dst" once ip6_route_input() or
         * skb_dst_drop() is called. However, in order to detect a dst loop, we
         * need the address of its lwtstate. So, save the address of lwtstate
         * now and use it later as a comparison.
         */
        lwtst = orig_dst->lwtstate;

        slwt = seg6_lwt_lwtunnel(lwtst);

        local_bh_disable();
        dst = dst_cache_get(&slwt->cache);
        local_bh_enable();

        err = seg6_do_srh(skb, dst);
        if (unlikely(err)) {
                dst_release(dst);
                goto drop;
        }

        if (!dst) {
                ip6_route_input(skb);
                dst = skb_dst(skb);

                /* cache only if we don't create a dst reference loop */
                if (!dst->error && lwtst != dst->lwtstate) {
                        local_bh_disable();
                        dst_cache_set_ip6(&slwt->cache, dst,
                                          &ipv6_hdr(skb)->saddr);
                        local_bh_enable();
                }

                err = skb_cow_head(skb, LL_RESERVED_SPACE(dst_dev(dst)));
                if (unlikely(err))
                        goto drop;
        } else {
                skb_dst_drop(skb);
                skb_dst_set(skb, dst);
        }

        if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
                return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT,
                               dev_net(skb->dev), NULL, skb, NULL,
                               skb_dst_dev(skb), seg6_input_finish);

        return seg6_input_finish(dev_net(skb->dev), NULL, skb);
drop:
        kfree_skb(skb);
        return err;
}

static int seg6_input_nf(struct sk_buff *skb)
{
        struct net_device *dev = skb_dst_dev(skb);
        struct net *net = dev_net(skb->dev);

        switch (skb->protocol) {
        case htons(ETH_P_IP):
                return NF_HOOK(NFPROTO_IPV4, NF_INET_POST_ROUTING, net, NULL,
                               skb, NULL, dev, seg6_input_core);
        case htons(ETH_P_IPV6):
                return NF_HOOK(NFPROTO_IPV6, NF_INET_POST_ROUTING, net, NULL,
                               skb, NULL, dev, seg6_input_core);
        }

        return -EINVAL;
}

static int seg6_input(struct sk_buff *skb)
{
        if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
                return seg6_input_nf(skb);

        return seg6_input_core(dev_net(skb->dev), NULL, skb);
}

static int seg6_output_core(struct net *net, struct sock *sk,
                            struct sk_buff *skb)
{
        struct dst_entry *orig_dst = skb_dst(skb);
        struct dst_entry *dst = NULL;
        struct seg6_lwt *slwt;
        int err;

        slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);

        local_bh_disable();
        dst = dst_cache_get(&slwt->cache);
        local_bh_enable();

        err = seg6_do_srh(skb, dst);
        if (unlikely(err))
                goto drop;

        if (unlikely(!dst)) {
                struct ipv6hdr *hdr = ipv6_hdr(skb);
                struct flowi6 fl6;

                memset(&fl6, 0, sizeof(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;
                        goto drop;
                }

                /* cache only if we don't create a dst reference loop */
                if (orig_dst->lwtstate != dst->lwtstate) {
                        local_bh_disable();
                        dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
                        local_bh_enable();
                }

                err = skb_cow_head(skb, LL_RESERVED_SPACE(dst_dev(dst)));
                if (unlikely(err))
                        goto drop;
        }

        skb_dst_drop(skb);
        skb_dst_set(skb, dst);

        if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
                return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT, net, sk, skb,
                               NULL, dst_dev(dst), dst_output);

        return dst_output(net, sk, skb);
drop:
        dst_release(dst);
        kfree_skb(skb);
        return err;
}

static int seg6_output_nf(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct net_device *dev = skb_dst_dev(skb);

        switch (skb->protocol) {
        case htons(ETH_P_IP):
                return NF_HOOK(NFPROTO_IPV4, NF_INET_POST_ROUTING, net, sk, skb,
                               NULL, dev, seg6_output_core);
        case htons(ETH_P_IPV6):
                return NF_HOOK(NFPROTO_IPV6, NF_INET_POST_ROUTING, net, sk, skb,
                               NULL, dev, seg6_output_core);
        }

        return -EINVAL;
}

static int seg6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
                return seg6_output_nf(net, sk, skb);

        return seg6_output_core(net, sk, skb);
}

static int seg6_build_state(struct net *net, struct nlattr *nla,
                            unsigned int family, const void *cfg,
                            struct lwtunnel_state **ts,
                            struct netlink_ext_ack *extack)
{
        struct nlattr *tb[SEG6_IPTUNNEL_MAX + 1];
        struct seg6_iptunnel_encap *tuninfo;
        struct lwtunnel_state *newts;
        int tuninfo_len, min_size;
        struct seg6_lwt *slwt;
        int err;

        if (family != AF_INET && family != AF_INET6)
                return -EINVAL;

        err = nla_parse_nested_deprecated(tb, SEG6_IPTUNNEL_MAX, nla,
                                          seg6_iptunnel_policy, extack);

        if (err < 0)
                return err;

        if (!tb[SEG6_IPTUNNEL_SRH])
                return -EINVAL;

        tuninfo = nla_data(tb[SEG6_IPTUNNEL_SRH]);
        tuninfo_len = nla_len(tb[SEG6_IPTUNNEL_SRH]);

        /* tuninfo must contain at least the iptunnel encap structure,
         * the SRH and one segment
         */
        min_size = sizeof(*tuninfo) + sizeof(struct ipv6_sr_hdr) +
                   sizeof(struct in6_addr);
        if (tuninfo_len < min_size)
                return -EINVAL;

        switch (tuninfo->mode) {
        case SEG6_IPTUN_MODE_INLINE:
                if (family != AF_INET6)
                        return -EINVAL;

                break;
        case SEG6_IPTUN_MODE_ENCAP:
                break;
        case SEG6_IPTUN_MODE_L2ENCAP:
                break;
        case SEG6_IPTUN_MODE_ENCAP_RED:
                break;
        case SEG6_IPTUN_MODE_L2ENCAP_RED:
                break;
        default:
                return -EINVAL;
        }

        /* verify that SRH is consistent */
        if (!seg6_validate_srh(tuninfo->srh, tuninfo_len - sizeof(*tuninfo), false))
                return -EINVAL;

        newts = lwtunnel_state_alloc(tuninfo_len + sizeof(*slwt));
        if (!newts)
                return -ENOMEM;

        slwt = seg6_lwt_lwtunnel(newts);

        err = dst_cache_init(&slwt->cache, GFP_ATOMIC);
        if (err) {
                kfree(newts);
                return err;
        }

        memcpy(&slwt->tuninfo, tuninfo, tuninfo_len);

        newts->type = LWTUNNEL_ENCAP_SEG6;
        newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;

        if (tuninfo->mode != SEG6_IPTUN_MODE_L2ENCAP)
                newts->flags |= LWTUNNEL_STATE_OUTPUT_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,
        .owner = THIS_MODULE,
};

int __init seg6_iptunnel_init(void)
{
        return lwtunnel_encap_add_ops(&seg6_iptun_ops, LWTUNNEL_ENCAP_SEG6);
}

void seg6_iptunnel_exit(void)
{
        lwtunnel_encap_del_ops(&seg6_iptun_ops, LWTUNNEL_ENCAP_SEG6);
}