/*-
 * Copyright (c) 2010-2011 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This material is based upon work partially supported by The
 * NetBSD Foundation under a contract with Mindaugas Rasiukevicius.
 *
 * 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.
 */

/*
 * NPF module for packet construction routines.
 */

#ifdef _KERNEL
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: npf_sendpkt.c,v 1.23 2023/02/12 13:38:37 kardel Exp $");

#include <sys/param.h>
#include <sys/types.h>

#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip_var.h>
#include <netinet/tcp.h>
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#include <sys/mbuf.h>
#endif

#include "npf_impl.h"

#define DEFAULT_IP_TTL          (ip_defttl)

#if defined(_NPF_STANDALONE)
#define m_gethdr(t, f)          (npf)->mbufops->alloc((npf), 0, 0)
#define m_freem(m)              (npc)->npc_ctx->mbufops->free(m)
#define mtod(m,t)               ((t)((npc)->npc_ctx->mbufops->getdata(m)))
#endif

#if !defined(INET6) || defined(_NPF_STANDALONE)
#define in6_cksum(...)          0
#define ip6_output(...)         0
#define icmp6_error(m, ...)     m_freem(m)
#define npf_ip6_setscope(n, i)  ((void)(i), 0)
#endif

#if defined(INET6)
static int
npf_ip6_setscope(const npf_cache_t *npc, struct ip6_hdr *ip6)
{
        const struct ifnet *rcvif = npc->npc_nbuf->nb_ifp;

        if (in6_clearscope(&ip6->ip6_src) || in6_clearscope(&ip6->ip6_dst)) {
                return EINVAL;
        }
        if (in6_setscope(&ip6->ip6_src, rcvif, NULL) ||
            in6_setscope(&ip6->ip6_dst, rcvif, NULL)) {
                return EINVAL;
        }
        return 0;
}
#endif

/*
 * npf_return_tcp: return a TCP reset (RST) packet.
 */
static int
npf_return_tcp(npf_cache_t *npc)
{
        npf_t *npf = npc->npc_ctx;
        struct mbuf *m;
        struct ip *ip = NULL;
        struct ip6_hdr *ip6 = NULL;
        struct tcphdr *oth, *th;
        tcp_seq seq, ack;
        int tcpdlen, len;
        uint32_t win;

        /* Fetch relevant data. */
        KASSERT(npf_iscached(npc, NPC_IP46));
        KASSERT(npf_iscached(npc, NPC_LAYER4));
        tcpdlen = npf_tcpsaw(npc, &seq, &ack, &win);
        oth = npc->npc_l4.tcp;

        if (oth->th_flags & TH_RST) {
                return 0;
        }

        /* Create and setup a network buffer. */
        if (npf_iscached(npc, NPC_IP4)) {
                len = sizeof(struct ip) + sizeof(struct tcphdr);
        } else if (npf_iscached(npc, NPC_IP6)) {
                len = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
        } else {
                return EINVAL;
        }

        m = m_gethdr(M_DONTWAIT, MT_HEADER);
        if (m == NULL) {
                return ENOMEM;
        }
#if !defined(_NPF_STANDALONE)
        m->m_data += max_linkhdr;
        m->m_len = len;
        m->m_pkthdr.len = len;
        (void)npf;
#endif
        if (npf_iscached(npc, NPC_IP4)) {
                struct ip *oip = npc->npc_ip.v4;

                ip = mtod(m, struct ip *);
                memset(ip, 0, len);

                /*
                 * First, partially fill IPv4 header for TCP checksum.
                 * Note: IP length contains TCP header length.
                 */
                ip->ip_p = IPPROTO_TCP;
                ip->ip_src.s_addr = oip->ip_dst.s_addr;
                ip->ip_dst.s_addr = oip->ip_src.s_addr;
                ip->ip_len = htons(sizeof(struct tcphdr));

                th = (struct tcphdr *)(ip + 1);
        } else {
                struct ip6_hdr *oip = npc->npc_ip.v6;

                KASSERT(npf_iscached(npc, NPC_IP6));
                ip6 = mtod(m, struct ip6_hdr *);
                memset(ip6, 0, len);

                ip6->ip6_nxt = IPPROTO_TCP;
                ip6->ip6_hlim = IPV6_DEFHLIM;
                memcpy(&ip6->ip6_src, &oip->ip6_dst, sizeof(struct in6_addr));
                memcpy(&ip6->ip6_dst, &oip->ip6_src, sizeof(struct in6_addr));
                ip6->ip6_plen = htons(len);
                ip6->ip6_vfc = IPV6_VERSION;

                th = (struct tcphdr *)(ip6 + 1);
        }

        /*
         * Construct TCP header and compute the checksum.
         */
        th->th_sport = oth->th_dport;
        th->th_dport = oth->th_sport;
        th->th_seq = htonl(ack);
        if (oth->th_flags & TH_SYN) {
                tcpdlen++;
        }
        th->th_ack = htonl(seq + tcpdlen);
        th->th_off = sizeof(struct tcphdr) >> 2;
        th->th_flags = TH_ACK | TH_RST;

        if (npf_iscached(npc, NPC_IP4)) {
                th->th_sum = in_cksum(m, len);

                /*
                 * Second, fill the rest of IPv4 header and correct IP length.
                 */
                ip->ip_v = IPVERSION;
                ip->ip_hl = sizeof(struct ip) >> 2;
                ip->ip_tos = IPTOS_LOWDELAY;
                ip->ip_len = htons(len);
                ip->ip_ttl = DEFAULT_IP_TTL;
        } else {
                KASSERT(npf_iscached(npc, NPC_IP6));
                th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
                    sizeof(struct tcphdr));

                /* Handle IPv6 scopes */
                if (npf_ip6_setscope(npc, ip6) != 0) {
                        goto bad;
                }
        }

        /* don't look at our generated reject packets going out */
        (void)npf_mbuf_add_tag(npc->npc_nbuf, m, NPF_NTAG_PASS);

        /* Pass to IP layer. */
        if (npf_iscached(npc, NPC_IP4)) {
                return ip_output(m, NULL, NULL, IP_FORWARDING, NULL, NULL);
        }
        return ip6_output(m, NULL, NULL, IPV6_FORWARDING, NULL, NULL, NULL);
bad:
        m_freem(m);
        return EINVAL;
}

/*
 * npf_return_icmp: return an ICMP error.
 */
static int
npf_return_icmp(const npf_cache_t *npc)
{
        struct mbuf *m = nbuf_head_mbuf(npc->npc_nbuf);

        /* don't look at our generated reject packets going out */
        (void)nbuf_add_tag(npc->npc_nbuf, NPF_NTAG_PASS);

        if (npf_iscached(npc, NPC_IP4)) {
                icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_ADMIN_PROHIBIT, 0, 0);
                return 0;
        } else if (npf_iscached(npc, NPC_IP6)) {
                /* Handle IPv6 scopes */
                struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);

                if (npf_ip6_setscope(npc, ip6) != 0) {
                        return EINVAL;
                }
                icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADMIN, 0);
                return 0;
        }
        return EINVAL;
}

/*
 * npf_return_block: return TCP reset or ICMP host unreachable packet.
 *
 * => Returns true if the buffer was consumed (freed) and false otherwise.
 */
bool
npf_return_block(npf_cache_t *npc, const int retfl)
{
        if (!npf_iscached(npc, NPC_IP46) || !npf_iscached(npc, NPC_LAYER4)) {
                return false;
        }
        switch (npc->npc_proto) {
        case IPPROTO_TCP:
                if (retfl & NPF_RULE_RETRST) {
                        (void)npf_return_tcp(npc);
                }
                break;
        case IPPROTO_UDP:
                if (retfl & NPF_RULE_RETICMP)
                        if (npf_return_icmp(npc) == 0)
                                return true;
                break;
        }
        return false;
}