/*      $NetBSD: in_l2tp.c,v 1.22 2023/09/01 11:23:39 andvar Exp $      */

/*
 * Copyright (c) 2017 Internet Initiative Japan Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: in_l2tp.c,v 1.22 2023/09/01 11:23:39 andvar Exp $");

#ifdef _KERNEL_OPT
#include "opt_l2tp.h"
#endif

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/mbuf.h>
#include <sys/errno.h>
#include <sys/ioctl.h>
#include <sys/syslog.h>
#include <sys/kernel.h>
#include <sys/socketvar.h> /* For softnet_lock */

#include <net/if.h>
#include <net/route.h>
#include <net/if_ether.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/ip_private.h>
#include <netinet/in_l2tp.h>
#include <netinet/in_var.h>
#include <netinet/ip_encap.h>

#ifdef ALTQ
#include <altq/altq.h>
#endif

/* TODO: IP_TCPMSS support */
#undef IP_TCPMSS
#ifdef IP_TCPMSS
#include <netinet/ip_tcpmss.h>
#endif

#include <net/if_l2tp.h>

int ip_l2tp_ttl = L2TP_TTL;

static void in_l2tp_input(struct mbuf *, int, int, void *);

static const struct encapsw in_l2tp_encapsw = {
        .encapsw4 = {
                .pr_input       = in_l2tp_input,
                .pr_ctlinput    = NULL,
        }
};

static int in_l2tp_match(struct mbuf *, int, int, void *);

int
in_l2tp_output(struct l2tp_variant *var, struct mbuf *m)
{
        struct l2tp_softc *sc;
        struct ifnet *ifp;
        struct sockaddr_in *sin_src = satosin(var->lv_psrc);
        struct sockaddr_in *sin_dst = satosin(var->lv_pdst);
        struct ip iphdr;        /* capsule IP header, host byte ordered */
        struct rtentry *rt;
        struct route *ro_pc;
        kmutex_t *lock_pc;

        int error;
        uint32_t sess_id;

        KASSERT(var != NULL);
        KASSERT(l2tp_heldref_variant(var));
        KASSERT(sin_src != NULL && sin_dst != NULL);
        KASSERT(sin_src->sin_family == AF_INET
            && sin_dst->sin_family == AF_INET);

        sc = var->lv_softc;
        ifp = &sc->l2tp_ec.ec_if;
        error = l2tp_check_nesting(ifp, m);
        if (error) {
                m_freem(m);
                goto looped;
        }

        /* bidirectional configured tunnel mode */
        if (sin_dst->sin_addr.s_addr == INADDR_ANY) {
                m_freem(m);
                if ((ifp->if_flags & IFF_DEBUG) != 0)
                        log(LOG_DEBUG, "%s: ENETUNREACH\n", __func__);
                error = ENETUNREACH;
                goto out;
        }

#ifdef NOTYET
/* TODO: support ALTQ for inner frame */
#ifdef ALTQ
        ALTQ_SAVE_PAYLOAD(m, AF_ETHER);
#endif
#endif

        memset(&iphdr, 0, sizeof(iphdr));
        iphdr.ip_src = sin_src->sin_addr;
        iphdr.ip_dst = sin_dst->sin_addr;
        iphdr.ip_p = IPPROTO_L2TP;
        /* version will be set in ip_output() */
        iphdr.ip_ttl = ip_l2tp_ttl;
        /* outer IP header length */
        iphdr.ip_len = sizeof(struct ip);
        /* session-id length */
        iphdr.ip_len += sizeof(uint32_t);
        if (var->lv_use_cookie == L2TP_COOKIE_ON) {
                /* cookie length */
                iphdr.ip_len += var->lv_peer_cookie_len;
        }

/* TODO: IP_TCPMSS support */
#ifdef IP_TCPMSS
        m = l2tp_tcpmss_clamp(ifp, m);
        if (m == NULL) {
                error = EINVAL;
                goto out;
        }
#endif

        /*
         * Payload length.
         *
         * NOTE: payload length may be changed in ip_tcpmss(). Typical case
         * is missing of TCP mss option in original TCP header.
         */
        iphdr.ip_len += m->m_pkthdr.len;
        HTONS(iphdr.ip_len);

        if (var->lv_use_cookie == L2TP_COOKIE_ON) {
                /* prepend session cookie */
                uint32_t cookie_32;
                uint64_t cookie_64;
                M_PREPEND(m, var->lv_peer_cookie_len, M_DONTWAIT);
                if (m && m->m_len < var->lv_peer_cookie_len)
                        m = m_pullup(m, var->lv_peer_cookie_len);
                if (m == NULL) {
                        error = ENOBUFS;
                        goto out;
                }
                if (var->lv_peer_cookie_len == 4) {
                        cookie_32 = htonl((uint32_t)var->lv_peer_cookie);
                        memcpy(mtod(m, void *), &cookie_32, sizeof(uint32_t));
                } else {
                        cookie_64 = htobe64(var->lv_peer_cookie);
                        memcpy(mtod(m, void *), &cookie_64, sizeof(uint64_t));
                }
        }

        /* prepend session-ID */
        sess_id = htonl(var->lv_peer_sess_id);
        M_PREPEND(m, sizeof(uint32_t), M_DONTWAIT);
        if (m && m->m_len < sizeof(uint32_t))
                m = m_pullup(m, sizeof(uint32_t));
        if (m == NULL) {
                error = ENOBUFS;
                goto out;
        }
        memcpy(mtod(m, uint32_t *), &sess_id, sizeof(uint32_t));

        /* prepend new IP header */
        M_PREPEND(m, sizeof(struct ip), M_DONTWAIT);
        if (m == NULL) {
                error = ENOBUFS;
                goto out;
        }
        if (M_GET_ALIGNED_HDR(&m, struct ip, false) != 0) {
                error = ENOBUFS;
                goto out;
        }
        memcpy(mtod(m, struct ip *), &iphdr, sizeof(struct ip));

        if_tunnel_get_ro(sc->l2tp_ro_percpu, &ro_pc, &lock_pc);
        if ((rt = rtcache_lookup(ro_pc, var->lv_pdst)) == NULL) {
                if_tunnel_put_ro(sc->l2tp_ro_percpu, lock_pc);
                m_freem(m);
                error = ENETUNREACH;
                goto out;
        }

        if (rt->rt_ifp == ifp) {
                rtcache_unref(rt, ro_pc);
                rtcache_free(ro_pc);
                if_tunnel_put_ro(sc->l2tp_ro_percpu, lock_pc);
                m_freem(m);
                error = ENETUNREACH;    /*XXX*/
                goto out;
        }
        rtcache_unref(rt, ro_pc);

        /*
         * To avoid inappropriate rewrite of checksum,
         * clear csum flags.
         */
        m->m_pkthdr.csum_flags  = 0;

        error = ip_output(m, NULL, ro_pc, 0, NULL, NULL);
        if_tunnel_put_ro(sc->l2tp_ro_percpu, lock_pc);
        return error;

looped:
        if (error)
                if_statinc(ifp, if_oerrors);

out:
        return error;
}

static void
in_l2tp_input(struct mbuf *m, int off, int proto, void *eparg __unused)
{
        struct ifnet *l2tpp = NULL;
        struct l2tp_softc *sc;
        uint32_t sess_id;
        uint32_t cookie_32;
        uint64_t cookie_64;
        struct psref psref;
        struct l2tp_variant *var;

        KASSERT((m->m_flags & M_PKTHDR) != 0);

        if (m->m_pkthdr.len < off + sizeof(uint32_t)) {
                m_freem(m);
                return;
        }

        /* get L2TP session ID */
        m_copydata(m, off, sizeof(uint32_t), (void *)&sess_id);
        NTOHL(sess_id);
#ifdef L2TP_DEBUG
        log(LOG_DEBUG, "%s: sess_id = %" PRIu32 "\n", __func__, sess_id);
#endif
        if (sess_id == 0) {
                /*
                 * L2TPv3 control packet received.
                 * userland daemon(l2tpd?) should process.
                 */
                SOFTNET_LOCK_IF_NET_MPSAFE();
                rip_input(m, off, proto);
                SOFTNET_UNLOCK_IF_NET_MPSAFE();
                return;
        }

        var = l2tp_lookup_session_ref(sess_id, &psref);
        if (var == NULL) {
                m_freem(m);
                ip_statinc(IP_STAT_NOL2TP);
                return;
        }

        sc = var->lv_softc;
        l2tpp = &(sc->l2tp_ec.ec_if);

        if (l2tpp == NULL || (l2tpp->if_flags & IFF_UP) == 0) {
#ifdef L2TP_DEBUG
                if (l2tpp == NULL)
                        log(LOG_DEBUG, "%s: l2tpp is NULL\n", __func__);
                else
                        log(LOG_DEBUG, "%s: l2tpp is down\n", __func__);
#endif
                m_freem(m);
                ip_statinc(IP_STAT_NOL2TP);
                goto out;
        }

        /* other CPU did l2tp_delete_tunnel */
        if (var->lv_psrc == NULL || var->lv_pdst == NULL) {
                m_freem(m);
                ip_statinc(IP_STAT_NOL2TP);
                goto out;
        }

        if (var->lv_state != L2TP_STATE_UP) {
                m_freem(m);
                goto out;
        }

        m_adj(m, off + sizeof(uint32_t));

        if (var->lv_use_cookie == L2TP_COOKIE_ON) {
                if (m->m_pkthdr.len < var->lv_my_cookie_len) {
                        m_freem(m);
                        goto out;
                }
                if (var->lv_my_cookie_len == 4) {
                        m_copydata(m, 0, sizeof(uint32_t), (void *)&cookie_32);
                        NTOHL(cookie_32);
                        if (cookie_32 != var->lv_my_cookie) {
                                m_freem(m);
                                goto out;
                        }
                        m_adj(m, sizeof(uint32_t));
                } else {
                        m_copydata(m, 0, sizeof(uint64_t), (void *)&cookie_64);
                        BE64TOH(cookie_64);
                        if (cookie_64 != var->lv_my_cookie) {
                                m_freem(m);
                                goto out;
                        }
                        m_adj(m, sizeof(uint64_t));
                }
        }

/* TODO: IP_TCPMSS support */
#ifdef IP_TCPMSS
        m = l2tp_tcpmss_clamp(l2tpp, m);
        if (m == NULL)
                goto out;
#endif
        l2tp_input(m, l2tpp);

out:
        l2tp_putref_variant(var, &psref);
        return;
}

/*
 * This function is used by encap4_lookup() to decide priority of the encaptab.
 * This priority is compared to the match length between mbuf's source/destination
 * IPv4 address pair and encaptab's one.
 * l2tp(4) does not use address pairs to search matched encaptab, so this
 * function must return the length bigger than or equals to IPv4 address pair to
 * avoid wrong encaptab.
 */
static int
in_l2tp_match(struct mbuf *m, int off, int proto, void *arg)
{
        struct l2tp_softc *sc = arg;
        struct l2tp_variant *var;
        struct psref psref;
        uint32_t sess_id;
        int rv = 0;

        KASSERT(proto == IPPROTO_L2TP);

        var = l2tp_getref_variant(sc, &psref);
        if (__predict_false(var == NULL))
                return rv;

        /*
         * If the packet contains no session ID it cannot match
         */
        if (m_length(m) < off + sizeof(uint32_t)) {
                rv = 0;
                goto out;
        }

        /* get L2TP session ID */
        m_copydata(m, off, sizeof(uint32_t), (void *)&sess_id);
        NTOHL(sess_id);
        if (sess_id == 0) {
                /*
                 * L2TPv3 control packet received.
                 * userland daemon(l2tpd?) should process.
                 */
                rv = 32 * 2;
        } else if (sess_id == var->lv_my_sess_id)
                rv = 32 * 2;
        else
                rv = 0;

out:
        l2tp_putref_variant(var, &psref);
        return rv;
}

int
in_l2tp_attach(struct l2tp_variant *var)
{
        struct l2tp_softc *sc = var->lv_softc;

        if (sc == NULL)
                return EINVAL;

        var->lv_encap_cookie = encap_attach_addr(AF_INET, IPPROTO_L2TP,
            var->lv_psrc, var->lv_pdst, in_l2tp_match, &in_l2tp_encapsw, sc);
        if (var->lv_encap_cookie == NULL)
                return EEXIST;

        return 0;
}

int
in_l2tp_detach(struct l2tp_variant *var)
{
        int error;

        error = encap_detach(var->lv_encap_cookie);
        if (error == 0)
                var->lv_encap_cookie = NULL;

        return error;
}