// 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 (*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);