// SPDX-License-Identifier: GPL-2.0-only
/* (C) 2001-2002 Magnus Boden <mb@ozaba.mine.nu>
 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/in.h>
#include <linux/udp.h>
#include <linux/netfilter.h>

#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_tuple.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_conntrack_ecache.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <linux/netfilter/nf_conntrack_tftp.h>

#define HELPER_NAME "tftp"

MODULE_AUTHOR("Magnus Boden <mb@ozaba.mine.nu>");
MODULE_DESCRIPTION("TFTP connection tracking helper");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ip_conntrack_tftp");
MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);

#define MAX_PORTS 8
static unsigned short ports[MAX_PORTS];
static unsigned int ports_c;
module_param_array(ports, ushort, &ports_c, 0400);
MODULE_PARM_DESC(ports, "Port numbers of TFTP servers");

unsigned int (__rcu *nf_nat_tftp_hook)(struct sk_buff *skb,
                                       enum ip_conntrack_info ctinfo,
                                       struct nf_conntrack_expect *exp)
                                       __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_tftp_hook);

static int tftp_help(struct sk_buff *skb,
                     unsigned int protoff,
                     struct nf_conn *ct,
                     enum ip_conntrack_info ctinfo)
{
        const struct tftphdr *tfh;
        struct tftphdr _tftph;
        struct nf_conntrack_expect *exp;
        struct nf_conntrack_tuple *tuple;
        unsigned int ret = NF_ACCEPT;
        typeof(nf_nat_tftp_hook) nf_nat_tftp;

        tfh = skb_header_pointer(skb, protoff + sizeof(struct udphdr),
                                 sizeof(_tftph), &_tftph);
        if (tfh == NULL)
                return NF_ACCEPT;

        switch (ntohs(tfh->opcode)) {
        case TFTP_OPCODE_READ:
        case TFTP_OPCODE_WRITE:
                /* RRQ and WRQ works the same way */
                nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
                nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);

                exp = nf_ct_expect_alloc(ct);
                if (exp == NULL) {
                        nf_ct_helper_log(skb, ct, "cannot alloc expectation");
                        return NF_DROP;
                }
                tuple = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
                nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
                                  nf_ct_l3num(ct),
                                  &tuple->src.u3, &tuple->dst.u3,
                                  IPPROTO_UDP, NULL, &tuple->dst.u.udp.port);

                pr_debug("expect: ");
                nf_ct_dump_tuple(&exp->tuple);

                nf_nat_tftp = rcu_dereference(nf_nat_tftp_hook);
                if (nf_nat_tftp && ct->status & IPS_NAT_MASK)
                        ret = nf_nat_tftp(skb, ctinfo, exp);
                else if (nf_ct_expect_related(exp, 0) != 0) {
                        nf_ct_helper_log(skb, ct, "cannot add expectation");
                        ret = NF_DROP;
                }
                nf_ct_expect_put(exp);
                break;
        case TFTP_OPCODE_DATA:
        case TFTP_OPCODE_ACK:
                pr_debug("Data/ACK opcode\n");
                break;
        case TFTP_OPCODE_ERROR:
                pr_debug("Error opcode\n");
                break;
        default:
                pr_debug("Unknown opcode\n");
        }
        return ret;
}

static struct nf_conntrack_helper tftp[MAX_PORTS * 2] __read_mostly;

static const struct nf_conntrack_expect_policy tftp_exp_policy = {
        .max_expected   = 1,
        .timeout        = 5 * 60,
};

static void __exit nf_conntrack_tftp_fini(void)
{
        nf_conntrack_helpers_unregister(tftp, ports_c * 2);
}

static int __init nf_conntrack_tftp_init(void)
{
        int i, ret;

        NF_CT_HELPER_BUILD_BUG_ON(0);

        if (ports_c == 0)
                ports[ports_c++] = TFTP_PORT;

        for (i = 0; i < ports_c; i++) {
                nf_ct_helper_init(&tftp[2 * i], AF_INET, IPPROTO_UDP,
                                  HELPER_NAME, TFTP_PORT, ports[i], i,
                                  &tftp_exp_policy, 0, tftp_help, NULL,
                                  THIS_MODULE);
                nf_ct_helper_init(&tftp[2 * i + 1], AF_INET6, IPPROTO_UDP,
                                  HELPER_NAME, TFTP_PORT, ports[i], i,
                                  &tftp_exp_policy, 0, tftp_help, NULL,
                                  THIS_MODULE);
        }

        ret = nf_conntrack_helpers_register(tftp, ports_c * 2);
        if (ret < 0) {
                pr_err("failed to register helpers\n");
                return ret;
        }
        return 0;
}

module_init(nf_conntrack_tftp_init);
module_exit(nf_conntrack_tftp_fini);