// 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);
}