// SPDX-License-Identifier: GPL-2.0-only
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/types.h>
#include <linux/module.h>
#include <net/ip.h>
#include <linux/ipv6.h>
#include <net/ipv6.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_tcpudp.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>

MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
MODULE_LICENSE("GPL");
MODULE_ALIAS("xt_tcp");
MODULE_ALIAS("xt_udp");
MODULE_ALIAS("ipt_udp");
MODULE_ALIAS("ipt_tcp");
MODULE_ALIAS("ip6t_udp");
MODULE_ALIAS("ip6t_tcp");

/* Returns 1 if the port is matched by the range, 0 otherwise */
static inline bool
port_match(u_int16_t min, u_int16_t max, u_int16_t port, bool invert)
{
        return (port >= min && port <= max) ^ invert;
}

static bool
tcp_find_option(u_int8_t option,
                const struct sk_buff *skb,
                unsigned int protoff,
                unsigned int optlen,
                bool invert,
                bool *hotdrop)
{
        /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
        const u_int8_t *op;
        u_int8_t _opt[60 - sizeof(struct tcphdr)];
        unsigned int i;

        pr_debug("finding option\n");

        if (!optlen)
                return invert;

        /* If we don't have the whole header, drop packet. */
        op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
                                optlen, _opt);
        if (op == NULL) {
                *hotdrop = true;
                return false;
        }

        for (i = 0; i < optlen; ) {
                if (op[i] == option) return !invert;
                if (op[i] < 2) i++;
                else i += op[i+1]?:1;
        }

        return invert;
}

static bool tcp_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
        const struct tcphdr *th;
        struct tcphdr _tcph;
        const struct xt_tcp *tcpinfo = par->matchinfo;

        if (par->fragoff != 0) {
                /* To quote Alan:

                   Don't allow a fragment of TCP 8 bytes in. Nobody normal
                   causes this. Its a cracker trying to break in by doing a
                   flag overwrite to pass the direction checks.
                */
                if (par->fragoff == 1) {
                        pr_debug("Dropping evil TCP offset=1 frag.\n");
                        par->hotdrop = true;
                }
                /* Must not be a fragment. */
                return false;
        }

        th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
        if (th == NULL) {
                /* We've been asked to examine this packet, and we
                   can't.  Hence, no choice but to drop. */
                pr_debug("Dropping evil TCP offset=0 tinygram.\n");
                par->hotdrop = true;
                return false;
        }

        if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
                        ntohs(th->source),
                        !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
                return false;
        if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
                        ntohs(th->dest),
                        !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
                return false;
        if (!NF_INVF(tcpinfo, XT_TCP_INV_FLAGS,
                     (((unsigned char *)th)[13] & tcpinfo->flg_mask) == tcpinfo->flg_cmp))
                return false;
        if (tcpinfo->option) {
                if (th->doff * 4 < sizeof(_tcph)) {
                        par->hotdrop = true;
                        return false;
                }
                if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
                                     th->doff*4 - sizeof(_tcph),
                                     tcpinfo->invflags & XT_TCP_INV_OPTION,
                                     &par->hotdrop))
                        return false;
        }
        return true;
}

static int tcp_mt_check(const struct xt_mtchk_param *par)
{
        const struct xt_tcp *tcpinfo = par->matchinfo;

        /* Must specify no unknown invflags */
        return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
}

static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
        const struct udphdr *uh;
        struct udphdr _udph;
        const struct xt_udp *udpinfo = par->matchinfo;

        /* Must not be a fragment. */
        if (par->fragoff != 0)
                return false;

        uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
        if (uh == NULL) {
                /* We've been asked to examine this packet, and we
                   can't.  Hence, no choice but to drop. */
                pr_debug("Dropping evil UDP tinygram.\n");
                par->hotdrop = true;
                return false;
        }

        return port_match(udpinfo->spts[0], udpinfo->spts[1],
                          ntohs(uh->source),
                          !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
                && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
                              ntohs(uh->dest),
                              !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
}

static int udp_mt_check(const struct xt_mtchk_param *par)
{
        const struct xt_udp *udpinfo = par->matchinfo;

        /* Must specify no unknown invflags */
        return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
}

static struct xt_match tcpudp_mt_reg[] __read_mostly = {
        {
                .name           = "tcp",
                .family         = NFPROTO_IPV4,
                .checkentry     = tcp_mt_check,
                .match          = tcp_mt,
                .matchsize      = sizeof(struct xt_tcp),
                .proto          = IPPROTO_TCP,
                .me             = THIS_MODULE,
        },
        {
                .name           = "tcp",
                .family         = NFPROTO_IPV6,
                .checkentry     = tcp_mt_check,
                .match          = tcp_mt,
                .matchsize      = sizeof(struct xt_tcp),
                .proto          = IPPROTO_TCP,
                .me             = THIS_MODULE,
        },
        {
                .name           = "udp",
                .family         = NFPROTO_IPV4,
                .checkentry     = udp_mt_check,
                .match          = udp_mt,
                .matchsize      = sizeof(struct xt_udp),
                .proto          = IPPROTO_UDP,
                .me             = THIS_MODULE,
        },
        {
                .name           = "udp",
                .family         = NFPROTO_IPV6,
                .checkentry     = udp_mt_check,
                .match          = udp_mt,
                .matchsize      = sizeof(struct xt_udp),
                .proto          = IPPROTO_UDP,
                .me             = THIS_MODULE,
        },
        {
                .name           = "udplite",
                .family         = NFPROTO_IPV4,
                .checkentry     = udp_mt_check,
                .match          = udp_mt,
                .matchsize      = sizeof(struct xt_udp),
                .proto          = IPPROTO_UDPLITE,
                .me             = THIS_MODULE,
        },
        {
                .name           = "udplite",
                .family         = NFPROTO_IPV6,
                .checkentry     = udp_mt_check,
                .match          = udp_mt,
                .matchsize      = sizeof(struct xt_udp),
                .proto          = IPPROTO_UDPLITE,
                .me             = THIS_MODULE,
        },
};

static int __init tcpudp_mt_init(void)
{
        return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
}

static void __exit tcpudp_mt_exit(void)
{
        xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
}

module_init(tcpudp_mt_init);
module_exit(tcpudp_mt_exit);