// SPDX-License-Identifier: GPL-2.0-only
/* FTP extension for TCP NAT alteration. */

/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/inet.h>
#include <linux/tcp.h>
#include <linux/netfilter_ipv4.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_helper.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <linux/netfilter/nf_conntrack_ftp.h>

#define NAT_HELPER_NAME "ftp"

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
MODULE_DESCRIPTION("ftp NAT helper");
MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);

/* FIXME: Time out? --RR */

static struct nf_conntrack_nat_helper nat_helper_ftp =
        NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);

static int nf_nat_ftp_fmt_cmd(struct nf_conn *ct, enum nf_ct_ftp_type type,
                              char *buffer, size_t buflen,
                              union nf_inet_addr *addr, u16 port)
{
        switch (type) {
        case NF_CT_FTP_PORT:
        case NF_CT_FTP_PASV:
                return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
                                ((unsigned char *)&addr->ip)[0],
                                ((unsigned char *)&addr->ip)[1],
                                ((unsigned char *)&addr->ip)[2],
                                ((unsigned char *)&addr->ip)[3],
                                port >> 8,
                                port & 0xFF);
        case NF_CT_FTP_EPRT:
                if (nf_ct_l3num(ct) == NFPROTO_IPV4)
                        return snprintf(buffer, buflen, "|1|%pI4|%u|",
                                        &addr->ip, port);
                else
                        return snprintf(buffer, buflen, "|2|%pI6|%u|",
                                        &addr->ip6, port);
        case NF_CT_FTP_EPSV:
                return snprintf(buffer, buflen, "|||%u|", port);
        }

        return 0;
}

/* So, this packet has hit the connection tracking matching code.
   Mangle it, and change the expectation to match the new version. */
static unsigned int nf_nat_ftp(struct sk_buff *skb,
                               enum ip_conntrack_info ctinfo,
                               enum nf_ct_ftp_type type,
                               unsigned int protoff,
                               unsigned int matchoff,
                               unsigned int matchlen,
                               struct nf_conntrack_expect *exp)
{
        union nf_inet_addr newaddr;
        u_int16_t port;
        int dir = CTINFO2DIR(ctinfo);
        struct nf_conn *ct = exp->master;
        char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
        unsigned int buflen;

        pr_debug("type %i, off %u len %u\n", type, matchoff, matchlen);

        /* Connection will come from wherever this packet goes, hence !dir */
        newaddr = ct->tuplehash[!dir].tuple.dst.u3;
        exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
        exp->dir = !dir;

        /* When you see the packet, we need to NAT it the same as the
         * this one. */
        exp->expectfn = nf_nat_follow_master;

        port = nf_nat_exp_find_port(exp, ntohs(exp->saved_proto.tcp.port));
        if (port == 0) {
                nf_ct_helper_log(skb, exp->master, "all ports in use");
                return NF_DROP;
        }

        buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
                                    &newaddr, port);
        if (!buflen)
                goto out;

        pr_debug("calling nf_nat_mangle_tcp_packet\n");

        if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
                                      matchlen, buffer, buflen))
                goto out;

        return NF_ACCEPT;

out:
        nf_ct_helper_log(skb, ct, "cannot mangle packet");
        nf_ct_unexpect_related(exp);
        return NF_DROP;
}

static void __exit nf_nat_ftp_fini(void)
{
        nf_nat_helper_unregister(&nat_helper_ftp);
        RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
        synchronize_rcu();
}

static int __init nf_nat_ftp_init(void)
{
        BUG_ON(nf_nat_ftp_hook != NULL);
        nf_nat_helper_register(&nat_helper_ftp);
        RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
        return 0;
}

/* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
static int warn_set(const char *val, const struct kernel_param *kp)
{
        pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
        return 0;
}
module_param_call(ports, warn_set, NULL, NULL, 0);

module_init(nf_nat_ftp_init);
module_exit(nf_nat_ftp_fini);