// SPDX-License-Identifier: GPL-2.0+
/*
 *  IPv6 IOAM Lightweight Tunnel implementation
 *
 *  Author:
 *  Justin Iurman <justin.iurman@uliege.be>
 */

#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/net.h>
#include <linux/in6.h>
#include <linux/ioam6.h>
#include <linux/ioam6_iptunnel.h>
#include <net/dst.h>
#include <net/sock.h>
#include <net/lwtunnel.h>
#include <net/ioam6.h>
#include <net/netlink.h>
#include <net/ipv6.h>
#include <net/dst_cache.h>
#include <net/ip6_route.h>
#include <net/addrconf.h>

struct ioam6_lwt_encap {
        struct ipv6_hopopt_hdr eh;
        u8 pad[2];                      /* 2-octet padding for 4n-alignment */
        struct ioam6_hdr ioamh;
        struct ioam6_trace_hdr traceh;
} __packed;

struct ioam6_lwt_freq {
        u32 k;
        u32 n;
};

struct ioam6_lwt {
        struct dst_entry null_dst;
        struct dst_cache cache;
        struct ioam6_lwt_freq freq;
        atomic_t pkt_cnt;
        u8 mode;
        bool has_tunsrc;
        struct in6_addr tunsrc;
        struct in6_addr tundst;
        struct ioam6_lwt_encap tuninfo;
};

static const struct netlink_range_validation freq_range = {
        .min = IOAM6_IPTUNNEL_FREQ_MIN,
        .max = IOAM6_IPTUNNEL_FREQ_MAX,
};

static struct ioam6_lwt *ioam6_lwt_state(struct lwtunnel_state *lwt)
{
        return (struct ioam6_lwt *)lwt->data;
}

static struct ioam6_lwt_encap *ioam6_lwt_info(struct lwtunnel_state *lwt)
{
        return &ioam6_lwt_state(lwt)->tuninfo;
}

static struct ioam6_trace_hdr *ioam6_lwt_trace(struct lwtunnel_state *lwt)
{
        return &(ioam6_lwt_state(lwt)->tuninfo.traceh);
}

static const struct nla_policy ioam6_iptunnel_policy[IOAM6_IPTUNNEL_MAX + 1] = {
        [IOAM6_IPTUNNEL_FREQ_K] = NLA_POLICY_FULL_RANGE(NLA_U32, &freq_range),
        [IOAM6_IPTUNNEL_FREQ_N] = NLA_POLICY_FULL_RANGE(NLA_U32, &freq_range),
        [IOAM6_IPTUNNEL_MODE]   = NLA_POLICY_RANGE(NLA_U8,
                                                   IOAM6_IPTUNNEL_MODE_MIN,
                                                   IOAM6_IPTUNNEL_MODE_MAX),
        [IOAM6_IPTUNNEL_SRC]    = NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)),
        [IOAM6_IPTUNNEL_DST]    = NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)),
        [IOAM6_IPTUNNEL_TRACE]  = NLA_POLICY_EXACT_LEN(
                                        sizeof(struct ioam6_trace_hdr)),
};

static bool ioam6_validate_trace_hdr(struct ioam6_trace_hdr *trace)
{
        u32 fields;

        if (!trace->type_be32 || !trace->remlen ||
            trace->remlen > IOAM6_TRACE_DATA_SIZE_MAX / 4 ||
            trace->type.bit12 | trace->type.bit13 | trace->type.bit14 |
            trace->type.bit15 | trace->type.bit16 | trace->type.bit17 |
            trace->type.bit18 | trace->type.bit19 | trace->type.bit20 |
            trace->type.bit21 | trace->type.bit23)
                return false;

        fields = be32_to_cpu(trace->type_be32);
        trace->nodelen = ioam6_trace_compute_nodelen(fields);

        return true;
}

static int ioam6_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[IOAM6_IPTUNNEL_MAX + 1];
        struct ioam6_lwt_encap *tuninfo;
        struct ioam6_trace_hdr *trace;
        struct lwtunnel_state *lwt;
        struct ioam6_lwt *ilwt;
        int len_aligned, err;
        u32 freq_k, freq_n;
        u8 mode;

        if (family != AF_INET6)
                return -EINVAL;

        err = nla_parse_nested(tb, IOAM6_IPTUNNEL_MAX, nla,
                               ioam6_iptunnel_policy, extack);
        if (err < 0)
                return err;

        if ((!tb[IOAM6_IPTUNNEL_FREQ_K] && tb[IOAM6_IPTUNNEL_FREQ_N]) ||
            (tb[IOAM6_IPTUNNEL_FREQ_K] && !tb[IOAM6_IPTUNNEL_FREQ_N])) {
                NL_SET_ERR_MSG(extack, "freq: missing parameter");
                return -EINVAL;
        } else if (!tb[IOAM6_IPTUNNEL_FREQ_K] && !tb[IOAM6_IPTUNNEL_FREQ_N]) {
                freq_k = IOAM6_IPTUNNEL_FREQ_MIN;
                freq_n = IOAM6_IPTUNNEL_FREQ_MIN;
        } else {
                freq_k = nla_get_u32(tb[IOAM6_IPTUNNEL_FREQ_K]);
                freq_n = nla_get_u32(tb[IOAM6_IPTUNNEL_FREQ_N]);

                if (freq_k > freq_n) {
                        NL_SET_ERR_MSG(extack, "freq: k > n is forbidden");
                        return -EINVAL;
                }
        }

        mode = nla_get_u8_default(tb[IOAM6_IPTUNNEL_MODE],
                                  IOAM6_IPTUNNEL_MODE_INLINE);

        if (tb[IOAM6_IPTUNNEL_SRC] && mode == IOAM6_IPTUNNEL_MODE_INLINE) {
                NL_SET_ERR_MSG(extack, "no tunnel src expected with this mode");
                return -EINVAL;
        }

        if (!tb[IOAM6_IPTUNNEL_DST] && mode != IOAM6_IPTUNNEL_MODE_INLINE) {
                NL_SET_ERR_MSG(extack, "this mode needs a tunnel destination");
                return -EINVAL;
        }

        if (!tb[IOAM6_IPTUNNEL_TRACE]) {
                NL_SET_ERR_MSG(extack, "missing trace");
                return -EINVAL;
        }

        trace = nla_data(tb[IOAM6_IPTUNNEL_TRACE]);
        if (!ioam6_validate_trace_hdr(trace)) {
                NL_SET_ERR_MSG_ATTR(extack, tb[IOAM6_IPTUNNEL_TRACE],
                                    "invalid trace validation");
                return -EINVAL;
        }

        len_aligned = ALIGN(trace->remlen * 4, 8);
        lwt = lwtunnel_state_alloc(sizeof(*ilwt) + len_aligned);
        if (!lwt)
                return -ENOMEM;

        ilwt = ioam6_lwt_state(lwt);
        err = dst_cache_init(&ilwt->cache, GFP_ATOMIC);
        if (err)
                goto free_lwt;

        /* This "fake" dst_entry will be stored in a dst_cache, which will call
         * dst_hold() and dst_release() on it. We must ensure that dst_destroy()
         * will never be called. For that, its initial refcount is 1 and +1 when
         * it is stored in the cache. Then, +1/-1 each time we read the cache
         * and release it. Long story short, we're fine.
         */
        dst_init(&ilwt->null_dst, NULL, NULL, DST_OBSOLETE_NONE, DST_NOCOUNT);

        atomic_set(&ilwt->pkt_cnt, 0);
        ilwt->freq.k = freq_k;
        ilwt->freq.n = freq_n;

        ilwt->mode = mode;

        if (!tb[IOAM6_IPTUNNEL_SRC]) {
                ilwt->has_tunsrc = false;
        } else {
                ilwt->has_tunsrc = true;
                ilwt->tunsrc = nla_get_in6_addr(tb[IOAM6_IPTUNNEL_SRC]);

                if (ipv6_addr_any(&ilwt->tunsrc)) {
                        NL_SET_ERR_MSG_ATTR(extack, tb[IOAM6_IPTUNNEL_SRC],
                                            "invalid tunnel source address");
                        err = -EINVAL;
                        goto free_cache;
                }
        }

        if (tb[IOAM6_IPTUNNEL_DST]) {
                ilwt->tundst = nla_get_in6_addr(tb[IOAM6_IPTUNNEL_DST]);

                if (ipv6_addr_any(&ilwt->tundst)) {
                        NL_SET_ERR_MSG_ATTR(extack, tb[IOAM6_IPTUNNEL_DST],
                                            "invalid tunnel dest address");
                        err = -EINVAL;
                        goto free_cache;
                }
        }

        tuninfo = ioam6_lwt_info(lwt);
        tuninfo->eh.hdrlen = ((sizeof(*tuninfo) + len_aligned) >> 3) - 1;
        tuninfo->pad[0] = IPV6_TLV_PADN;
        tuninfo->ioamh.type = IOAM6_TYPE_PREALLOC;
        tuninfo->ioamh.opt_type = IPV6_TLV_IOAM;
        tuninfo->ioamh.opt_len = sizeof(tuninfo->ioamh) - 2 + sizeof(*trace)
                                        + trace->remlen * 4;

        memcpy(&tuninfo->traceh, trace, sizeof(*trace));

        if (len_aligned - trace->remlen * 4) {
                tuninfo->traceh.data[trace->remlen * 4] = IPV6_TLV_PADN;
                tuninfo->traceh.data[trace->remlen * 4 + 1] = 2;
        }

        lwt->type = LWTUNNEL_ENCAP_IOAM6;
        lwt->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;

        *ts = lwt;

        return 0;
free_cache:
        dst_cache_destroy(&ilwt->cache);
free_lwt:
        kfree(lwt);
        return err;
}

static int ioam6_do_fill(struct net *net, struct sk_buff *skb)
{
        struct ioam6_trace_hdr *trace;
        struct ioam6_namespace *ns;

        trace = (struct ioam6_trace_hdr *)(skb_transport_header(skb)
                                           + sizeof(struct ipv6_hopopt_hdr) + 2
                                           + sizeof(struct ioam6_hdr));

        ns = ioam6_namespace(net, trace->namespace_id);
        if (ns)
                ioam6_fill_trace_data(skb, ns, trace, false);

        return 0;
}

static int ioam6_do_inline(struct net *net, struct sk_buff *skb,
                           struct ioam6_lwt_encap *tuninfo,
                           struct dst_entry *cache_dst)
{
        struct ipv6hdr *oldhdr, *hdr;
        int hdrlen, err;

        hdrlen = (tuninfo->eh.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(*oldhdr));
        skb_postpull_rcsum(skb, skb_network_header(skb), sizeof(*oldhdr));

        skb_push(skb, sizeof(*oldhdr) + hdrlen);
        skb_reset_network_header(skb);
        skb_mac_header_rebuild(skb);

        hdr = ipv6_hdr(skb);
        memmove(hdr, oldhdr, sizeof(*oldhdr));
        tuninfo->eh.nexthdr = hdr->nexthdr;

        skb_set_transport_header(skb, sizeof(*hdr));
        skb_postpush_rcsum(skb, hdr, sizeof(*hdr) + hdrlen);

        memcpy(skb_transport_header(skb), (u8 *)tuninfo, hdrlen);

        hdr->nexthdr = NEXTHDR_HOP;
        hdr->payload_len = cpu_to_be16(skb->len - sizeof(*hdr));

        return ioam6_do_fill(net, skb);
}

static int ioam6_do_encap(struct net *net, struct sk_buff *skb,
                          struct ioam6_lwt_encap *tuninfo,
                          bool has_tunsrc,
                          struct in6_addr *tunsrc,
                          struct in6_addr *tundst,
                          struct dst_entry *cache_dst)
{
        struct dst_entry *dst = skb_dst(skb);
        struct ipv6hdr *hdr, *inner_hdr;
        int hdrlen, len, err;

        hdrlen = (tuninfo->eh.hdrlen + 1) << 3;
        len = sizeof(*hdr) + hdrlen;

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

        inner_hdr = ipv6_hdr(skb);

        skb_push(skb, len);
        skb_reset_network_header(skb);
        skb_mac_header_rebuild(skb);
        skb_set_transport_header(skb, sizeof(*hdr));

        tuninfo->eh.nexthdr = NEXTHDR_IPV6;
        memcpy(skb_transport_header(skb), (u8 *)tuninfo, hdrlen);

        hdr = ipv6_hdr(skb);
        memcpy(hdr, inner_hdr, sizeof(*hdr));

        hdr->nexthdr = NEXTHDR_HOP;
        hdr->payload_len = cpu_to_be16(skb->len - sizeof(*hdr));
        hdr->daddr = *tundst;

        if (has_tunsrc)
                memcpy(&hdr->saddr, tunsrc, sizeof(*tunsrc));
        else
                ipv6_dev_get_saddr(net, dst_dev(dst), &hdr->daddr,
                                   IPV6_PREFER_SRC_PUBLIC, &hdr->saddr);

        skb_postpush_rcsum(skb, hdr, len);

        return ioam6_do_fill(net, skb);
}

static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct dst_entry *orig_dst = skb_dst(skb);
        struct dst_entry *dst = NULL;
        struct ioam6_lwt *ilwt;
        int err = -EINVAL;
        u32 pkt_cnt;

        if (skb->protocol != htons(ETH_P_IPV6))
                goto drop;

        ilwt = ioam6_lwt_state(orig_dst->lwtstate);

        /* Check for insertion frequency (i.e., "k over n" insertions) */
        pkt_cnt = atomic_fetch_inc(&ilwt->pkt_cnt);
        if (pkt_cnt % ilwt->freq.n >= ilwt->freq.k)
                goto out;

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

        /* This is how we notify that the destination does not change after
         * transformation and that we need to use orig_dst instead of the cache
         */
        if (dst == &ilwt->null_dst) {
                dst_release(dst);

                dst = orig_dst;
                /* keep refcount balance: dst_release() is called at the end */
                dst_hold(dst);
        }

        switch (ilwt->mode) {
        case IOAM6_IPTUNNEL_MODE_INLINE:
do_inline:
                /* Direct insertion - if there is no Hop-by-Hop yet */
                if (ipv6_hdr(skb)->nexthdr == NEXTHDR_HOP)
                        goto out;

                err = ioam6_do_inline(net, skb, &ilwt->tuninfo, dst);
                if (unlikely(err))
                        goto drop;

                break;
        case IOAM6_IPTUNNEL_MODE_ENCAP:
do_encap:
                /* Encapsulation (ip6ip6) */
                err = ioam6_do_encap(net, skb, &ilwt->tuninfo,
                                     ilwt->has_tunsrc, &ilwt->tunsrc,
                                     &ilwt->tundst, dst);
                if (unlikely(err))
                        goto drop;

                break;
        case IOAM6_IPTUNNEL_MODE_AUTO:
                /* Automatic (RFC8200 compliant):
                 *  - local packets -> INLINE mode
                 *  - in-transit packets -> ENCAP mode
                 */
                if (!skb->dev)
                        goto do_inline;

                goto do_encap;
        default:
                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;
                }

                /* If the destination is the same after transformation (which is
                 * a valid use case for IOAM), then we don't want to add it to
                 * the cache in order to avoid a reference loop. Instead, we add
                 * our fake dst_entry to the cache as a way to detect this case.
                 * Otherwise, we add the resolved destination to the cache.
                 */
                local_bh_disable();
                if (orig_dst->lwtstate == dst->lwtstate)
                        dst_cache_set_ip6(&ilwt->cache,
                                          &ilwt->null_dst, &fl6.saddr);
                else
                        dst_cache_set_ip6(&ilwt->cache, dst, &fl6.saddr);
                local_bh_enable();

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

        /* avoid lwtunnel_output() reentry loop when destination is the same
         * after transformation (e.g., with the inline mode)
         */
        if (orig_dst->lwtstate != dst->lwtstate) {
                skb_dst_drop(skb);
                skb_dst_set(skb, dst);
                return dst_output(net, sk, skb);
        }
out:
        dst_release(dst);
        return orig_dst->lwtstate->orig_output(net, sk, skb);
drop:
        dst_release(dst);
        kfree_skb(skb);
        return err;
}

static void ioam6_destroy_state(struct lwtunnel_state *lwt)
{
        /* Since the refcount of per-cpu dst_entry caches will never be 0 (see
         * why above) when our "fake" dst_entry is used, it is not necessary to
         * remove them before calling dst_cache_destroy()
         */
        dst_cache_destroy(&ioam6_lwt_state(lwt)->cache);
}

static int ioam6_fill_encap_info(struct sk_buff *skb,
                                 struct lwtunnel_state *lwtstate)
{
        struct ioam6_lwt *ilwt = ioam6_lwt_state(lwtstate);
        int err;

        err = nla_put_u32(skb, IOAM6_IPTUNNEL_FREQ_K, ilwt->freq.k);
        if (err)
                goto ret;

        err = nla_put_u32(skb, IOAM6_IPTUNNEL_FREQ_N, ilwt->freq.n);
        if (err)
                goto ret;

        err = nla_put_u8(skb, IOAM6_IPTUNNEL_MODE, ilwt->mode);
        if (err)
                goto ret;

        if (ilwt->mode != IOAM6_IPTUNNEL_MODE_INLINE) {
                if (ilwt->has_tunsrc) {
                        err = nla_put_in6_addr(skb, IOAM6_IPTUNNEL_SRC,
                                               &ilwt->tunsrc);
                        if (err)
                                goto ret;
                }

                err = nla_put_in6_addr(skb, IOAM6_IPTUNNEL_DST, &ilwt->tundst);
                if (err)
                        goto ret;
        }

        err = nla_put(skb, IOAM6_IPTUNNEL_TRACE, sizeof(ilwt->tuninfo.traceh),
                      &ilwt->tuninfo.traceh);
ret:
        return err;
}

static int ioam6_encap_nlsize(struct lwtunnel_state *lwtstate)
{
        struct ioam6_lwt *ilwt = ioam6_lwt_state(lwtstate);
        int nlsize;

        nlsize = nla_total_size(sizeof(ilwt->freq.k)) +
                  nla_total_size(sizeof(ilwt->freq.n)) +
                  nla_total_size(sizeof(ilwt->mode)) +
                  nla_total_size(sizeof(ilwt->tuninfo.traceh));

        if (ilwt->mode != IOAM6_IPTUNNEL_MODE_INLINE) {
                if (ilwt->has_tunsrc)
                        nlsize += nla_total_size(sizeof(ilwt->tunsrc));

                nlsize += nla_total_size(sizeof(ilwt->tundst));
        }

        return nlsize;
}

static int ioam6_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
{
        struct ioam6_trace_hdr *trace_a = ioam6_lwt_trace(a);
        struct ioam6_trace_hdr *trace_b = ioam6_lwt_trace(b);
        struct ioam6_lwt *ilwt_a = ioam6_lwt_state(a);
        struct ioam6_lwt *ilwt_b = ioam6_lwt_state(b);

        return (ilwt_a->freq.k != ilwt_b->freq.k ||
                ilwt_a->freq.n != ilwt_b->freq.n ||
                ilwt_a->mode != ilwt_b->mode ||
                ilwt_a->has_tunsrc != ilwt_b->has_tunsrc ||
                (ilwt_a->mode != IOAM6_IPTUNNEL_MODE_INLINE &&
                 !ipv6_addr_equal(&ilwt_a->tundst, &ilwt_b->tundst)) ||
                (ilwt_a->mode != IOAM6_IPTUNNEL_MODE_INLINE &&
                 ilwt_a->has_tunsrc &&
                 !ipv6_addr_equal(&ilwt_a->tunsrc, &ilwt_b->tunsrc)) ||
                trace_a->namespace_id != trace_b->namespace_id);
}

static const struct lwtunnel_encap_ops ioam6_iptun_ops = {
        .build_state            = ioam6_build_state,
        .destroy_state          = ioam6_destroy_state,
        .output                 = ioam6_output,
        .fill_encap             = ioam6_fill_encap_info,
        .get_encap_size         = ioam6_encap_nlsize,
        .cmp_encap              = ioam6_encap_cmp,
        .owner                  = THIS_MODULE,
};

int __init ioam6_iptunnel_init(void)
{
        return lwtunnel_encap_add_ops(&ioam6_iptun_ops, LWTUNNEL_ENCAP_IOAM6);
}

void ioam6_iptunnel_exit(void)
{
        lwtunnel_encap_del_ops(&ioam6_iptun_ops, LWTUNNEL_ENCAP_IOAM6);
}