// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C)2003-2006 Helsinki University of Technology
 * Copyright (C)2003-2006 USAGI/WIDE Project
 */
/*
 * Authors:
 *      Noriaki TAKAMIYA @USAGI
 *      Masahide NAKAMURA @USAGI
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/time.h>
#include <linux/ipv6.h>
#include <linux/icmpv6.h>
#include <net/sock.h>
#include <net/ipv6.h>
#include <net/ip6_checksum.h>
#include <net/rawv6.h>
#include <net/xfrm.h>
#include <net/mip6.h>

static inline unsigned int calc_padlen(unsigned int len, unsigned int n)
{
        return (n - len + 16) & 0x7;
}

static inline void *mip6_padn(__u8 *data, __u8 padlen)
{
        if (!data)
                return NULL;
        if (padlen == 1) {
                data[0] = IPV6_TLV_PAD1;
        } else if (padlen > 1) {
                data[0] = IPV6_TLV_PADN;
                data[1] = padlen - 2;
                if (padlen > 2)
                        memset(data+2, 0, data[1]);
        }
        return data + padlen;
}

static inline void mip6_param_prob(struct sk_buff *skb, u8 code, int pos)
{
        icmpv6_send(skb, ICMPV6_PARAMPROB, code, pos);
}

static int mip6_mh_len(int type)
{
        int len = 0;

        switch (type) {
        case IP6_MH_TYPE_BRR:
                len = 0;
                break;
        case IP6_MH_TYPE_HOTI:
        case IP6_MH_TYPE_COTI:
        case IP6_MH_TYPE_BU:
        case IP6_MH_TYPE_BACK:
                len = 1;
                break;
        case IP6_MH_TYPE_HOT:
        case IP6_MH_TYPE_COT:
        case IP6_MH_TYPE_BERROR:
                len = 2;
                break;
        }
        return len;
}

static int mip6_mh_filter(struct sock *sk, struct sk_buff *skb)
{
        struct ip6_mh _hdr;
        const struct ip6_mh *mh;

        mh = skb_header_pointer(skb, skb_transport_offset(skb),
                                sizeof(_hdr), &_hdr);
        if (!mh)
                return -1;

        if (((mh->ip6mh_hdrlen + 1) << 3) > skb->len)
                return -1;

        if (mh->ip6mh_hdrlen < mip6_mh_len(mh->ip6mh_type)) {
                net_dbg_ratelimited("mip6: MH message too short: %d vs >=%d\n",
                                    mh->ip6mh_hdrlen,
                                    mip6_mh_len(mh->ip6mh_type));
                mip6_param_prob(skb, 0, offsetof(struct ip6_mh, ip6mh_hdrlen) +
                                skb_network_header_len(skb));
                return -1;
        }

        if (mh->ip6mh_proto != IPPROTO_NONE) {
                net_dbg_ratelimited("mip6: MH invalid payload proto = %d\n",
                                    mh->ip6mh_proto);
                mip6_param_prob(skb, 0, offsetof(struct ip6_mh, ip6mh_proto) +
                                skb_network_header_len(skb));
                return -1;
        }

        return 0;
}

struct mip6_report_rate_limiter {
        spinlock_t lock;
        ktime_t stamp;
        int iif;
        struct in6_addr src;
        struct in6_addr dst;
};

static struct mip6_report_rate_limiter mip6_report_rl = {
        .lock = __SPIN_LOCK_UNLOCKED(mip6_report_rl.lock)
};

static int mip6_destopt_input(struct xfrm_state *x, struct sk_buff *skb)
{
        const struct ipv6hdr *iph = ipv6_hdr(skb);
        struct ipv6_destopt_hdr *destopt = (struct ipv6_destopt_hdr *)skb->data;
        int err = destopt->nexthdr;

        spin_lock(&x->lock);
        if (!ipv6_addr_equal(&iph->saddr, (struct in6_addr *)x->coaddr) &&
            !ipv6_addr_any((struct in6_addr *)x->coaddr))
                err = -ENOENT;
        spin_unlock(&x->lock);

        return err;
}

/* Destination Option Header is inserted.
 * IP Header's src address is replaced with Home Address Option in
 * Destination Option Header.
 */
static int mip6_destopt_output(struct xfrm_state *x, struct sk_buff *skb)
{
        struct ipv6hdr *iph;
        struct ipv6_destopt_hdr *dstopt;
        struct ipv6_destopt_hao *hao;
        u8 nexthdr;
        int len;

        skb_push(skb, -skb_network_offset(skb));
        iph = ipv6_hdr(skb);

        nexthdr = *skb_mac_header(skb);
        *skb_mac_header(skb) = IPPROTO_DSTOPTS;

        dstopt = (struct ipv6_destopt_hdr *)skb_transport_header(skb);
        dstopt->nexthdr = nexthdr;

        hao = mip6_padn((char *)(dstopt + 1),
                        calc_padlen(sizeof(*dstopt), 6));

        hao->type = IPV6_TLV_HAO;
        BUILD_BUG_ON(sizeof(*hao) != 18);
        hao->length = sizeof(*hao) - 2;

        len = ((char *)hao - (char *)dstopt) + sizeof(*hao);

        memcpy(&hao->addr, &iph->saddr, sizeof(hao->addr));
        spin_lock_bh(&x->lock);
        memcpy(&iph->saddr, x->coaddr, sizeof(iph->saddr));
        spin_unlock_bh(&x->lock);

        WARN_ON(len != x->props.header_len);
        dstopt->hdrlen = (x->props.header_len >> 3) - 1;

        return 0;
}

static inline int mip6_report_rl_allow(ktime_t stamp,
                                       const struct in6_addr *dst,
                                       const struct in6_addr *src, int iif)
{
        int allow = 0;

        spin_lock_bh(&mip6_report_rl.lock);
        if (mip6_report_rl.stamp != stamp ||
            mip6_report_rl.iif != iif ||
            !ipv6_addr_equal(&mip6_report_rl.src, src) ||
            !ipv6_addr_equal(&mip6_report_rl.dst, dst)) {
                mip6_report_rl.stamp = stamp;
                mip6_report_rl.iif = iif;
                mip6_report_rl.src = *src;
                mip6_report_rl.dst = *dst;
                allow = 1;
        }
        spin_unlock_bh(&mip6_report_rl.lock);
        return allow;
}

static int mip6_destopt_reject(struct xfrm_state *x, struct sk_buff *skb,
                               const struct flowi *fl)
{
        struct net *net = xs_net(x);
        struct inet6_skb_parm *opt = (struct inet6_skb_parm *)skb->cb;
        const struct flowi6 *fl6 = &fl->u.ip6;
        struct ipv6_destopt_hao *hao = NULL;
        struct xfrm_selector sel;
        int offset;
        ktime_t stamp;
        int err = 0;

        if (unlikely(fl6->flowi6_proto == IPPROTO_MH &&
                     fl6->fl6_mh_type <= IP6_MH_TYPE_MAX))
                goto out;

        if (likely(opt->dsthao)) {
                offset = ipv6_find_tlv(skb, opt->dsthao, IPV6_TLV_HAO);
                if (likely(offset >= 0))
                        hao = (struct ipv6_destopt_hao *)
                                        (skb_network_header(skb) + offset);
        }

        stamp = skb_get_ktime(skb);

        if (!mip6_report_rl_allow(stamp, &ipv6_hdr(skb)->daddr,
                                  hao ? &hao->addr : &ipv6_hdr(skb)->saddr,
                                  opt->iif))
                goto out;

        memset(&sel, 0, sizeof(sel));
        memcpy(&sel.daddr, (xfrm_address_t *)&ipv6_hdr(skb)->daddr,
               sizeof(sel.daddr));
        sel.prefixlen_d = 128;
        memcpy(&sel.saddr, (xfrm_address_t *)&ipv6_hdr(skb)->saddr,
               sizeof(sel.saddr));
        sel.prefixlen_s = 128;
        sel.family = AF_INET6;
        sel.proto = fl6->flowi6_proto;
        sel.dport = xfrm_flowi_dport(fl, &fl6->uli);
        if (sel.dport)
                sel.dport_mask = htons(~0);
        sel.sport = xfrm_flowi_sport(fl, &fl6->uli);
        if (sel.sport)
                sel.sport_mask = htons(~0);
        sel.ifindex = fl6->flowi6_oif;

        err = km_report(net, IPPROTO_DSTOPTS, &sel,
                        (hao ? (xfrm_address_t *)&hao->addr : NULL));

 out:
        return err;
}

static int mip6_destopt_init_state(struct xfrm_state *x, struct netlink_ext_ack *extack)
{
        if (x->id.spi) {
                NL_SET_ERR_MSG(extack, "SPI must be 0");
                return -EINVAL;
        }
        if (x->props.mode != XFRM_MODE_ROUTEOPTIMIZATION) {
                NL_SET_ERR_MSG(extack, "XFRM mode must be XFRM_MODE_ROUTEOPTIMIZATION");
                return -EINVAL;
        }

        x->props.header_len = sizeof(struct ipv6_destopt_hdr) +
                calc_padlen(sizeof(struct ipv6_destopt_hdr), 6) +
                sizeof(struct ipv6_destopt_hao);
        WARN_ON(x->props.header_len != 24);

        return 0;
}

/*
 * Do nothing about destroying since it has no specific operation for
 * destination options header unlike IPsec protocols.
 */
static void mip6_destopt_destroy(struct xfrm_state *x)
{
}

static const struct xfrm_type mip6_destopt_type = {
        .owner          = THIS_MODULE,
        .proto          = IPPROTO_DSTOPTS,
        .flags          = XFRM_TYPE_NON_FRAGMENT | XFRM_TYPE_LOCAL_COADDR,
        .init_state     = mip6_destopt_init_state,
        .destructor     = mip6_destopt_destroy,
        .input          = mip6_destopt_input,
        .output         = mip6_destopt_output,
        .reject         = mip6_destopt_reject,
};

static int mip6_rthdr_input(struct xfrm_state *x, struct sk_buff *skb)
{
        const struct ipv6hdr *iph = ipv6_hdr(skb);
        struct rt2_hdr *rt2 = (struct rt2_hdr *)skb->data;
        int err = rt2->rt_hdr.nexthdr;

        spin_lock(&x->lock);
        if (!ipv6_addr_equal(&iph->daddr, (struct in6_addr *)x->coaddr) &&
            !ipv6_addr_any((struct in6_addr *)x->coaddr))
                err = -ENOENT;
        spin_unlock(&x->lock);

        return err;
}

/* Routing Header type 2 is inserted.
 * IP Header's dst address is replaced with Routing Header's Home Address.
 */
static int mip6_rthdr_output(struct xfrm_state *x, struct sk_buff *skb)
{
        struct ipv6hdr *iph;
        struct rt2_hdr *rt2;
        u8 nexthdr;

        skb_push(skb, -skb_network_offset(skb));
        iph = ipv6_hdr(skb);

        nexthdr = *skb_mac_header(skb);
        *skb_mac_header(skb) = IPPROTO_ROUTING;

        rt2 = (struct rt2_hdr *)skb_transport_header(skb);
        rt2->rt_hdr.nexthdr = nexthdr;
        rt2->rt_hdr.hdrlen = (x->props.header_len >> 3) - 1;
        rt2->rt_hdr.type = IPV6_SRCRT_TYPE_2;
        rt2->rt_hdr.segments_left = 1;
        memset(&rt2->reserved, 0, sizeof(rt2->reserved));

        WARN_ON(rt2->rt_hdr.hdrlen != 2);

        memcpy(&rt2->addr, &iph->daddr, sizeof(rt2->addr));
        spin_lock_bh(&x->lock);
        memcpy(&iph->daddr, x->coaddr, sizeof(iph->daddr));
        spin_unlock_bh(&x->lock);

        return 0;
}

static int mip6_rthdr_init_state(struct xfrm_state *x, struct netlink_ext_ack *extack)
{
        if (x->id.spi) {
                NL_SET_ERR_MSG(extack, "SPI must be 0");
                return -EINVAL;
        }
        if (x->props.mode != XFRM_MODE_ROUTEOPTIMIZATION) {
                NL_SET_ERR_MSG(extack, "XFRM mode must be XFRM_MODE_ROUTEOPTIMIZATION");
                return -EINVAL;
        }

        x->props.header_len = sizeof(struct rt2_hdr);

        return 0;
}

/*
 * Do nothing about destroying since it has no specific operation for routing
 * header type 2 unlike IPsec protocols.
 */
static void mip6_rthdr_destroy(struct xfrm_state *x)
{
}

static const struct xfrm_type mip6_rthdr_type = {
        .owner          = THIS_MODULE,
        .proto          = IPPROTO_ROUTING,
        .flags          = XFRM_TYPE_NON_FRAGMENT | XFRM_TYPE_REMOTE_COADDR,
        .init_state     = mip6_rthdr_init_state,
        .destructor     = mip6_rthdr_destroy,
        .input          = mip6_rthdr_input,
        .output         = mip6_rthdr_output,
};

static int __init mip6_init(void)
{
        pr_info("Mobile IPv6\n");

        if (xfrm_register_type(&mip6_destopt_type, AF_INET6) < 0) {
                pr_info("%s: can't add xfrm type(destopt)\n", __func__);
                goto mip6_destopt_xfrm_fail;
        }
        if (xfrm_register_type(&mip6_rthdr_type, AF_INET6) < 0) {
                pr_info("%s: can't add xfrm type(rthdr)\n", __func__);
                goto mip6_rthdr_xfrm_fail;
        }
        if (rawv6_mh_filter_register(mip6_mh_filter) < 0) {
                pr_info("%s: can't add rawv6 mh filter\n", __func__);
                goto mip6_rawv6_mh_fail;
        }


        return 0;

 mip6_rawv6_mh_fail:
        xfrm_unregister_type(&mip6_rthdr_type, AF_INET6);
 mip6_rthdr_xfrm_fail:
        xfrm_unregister_type(&mip6_destopt_type, AF_INET6);
 mip6_destopt_xfrm_fail:
        return -EAGAIN;
}

static void __exit mip6_fini(void)
{
        if (rawv6_mh_filter_unregister(mip6_mh_filter) < 0)
                pr_info("%s: can't remove rawv6 mh filter\n", __func__);
        xfrm_unregister_type(&mip6_rthdr_type, AF_INET6);
        xfrm_unregister_type(&mip6_destopt_type, AF_INET6);
}

module_init(mip6_init);
module_exit(mip6_fini);

MODULE_DESCRIPTION("IPv6 Mobility driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_XFRM_TYPE(AF_INET6, XFRM_PROTO_DSTOPTS);
MODULE_ALIAS_XFRM_TYPE(AF_INET6, XFRM_PROTO_ROUTING);