nf_nat_ftp.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/* FTP extension for TCP NAT alteration. */
  3
  4/* (C) 1999-2001 Paul `Rusty' Russell
  5 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
  6 */
  7
  8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  9
 10#include <linux/module.h>
 11#include <linux/moduleparam.h>
 12#include <linux/inet.h>
 13#include <linux/tcp.h>
 14#include <linux/netfilter_ipv4.h>
 15#include <net/netfilter/nf_nat.h>
 16#include <net/netfilter/nf_nat_helper.h>
 17#include <net/netfilter/nf_conntrack_helper.h>
 18#include <net/netfilter/nf_conntrack_expect.h>
 19#include <linux/netfilter/nf_conntrack_ftp.h>
 20
 21#define NAT_HELPER_NAME "ftp"
 22
 23MODULE_LICENSE("GPL");
 24MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
 25MODULE_DESCRIPTION("ftp NAT helper");
 26MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
 27
 28/* FIXME: Time out? --RR */
 29
 30static struct nf_conntrack_nat_helper nat_helper_ftp =
 31	NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
 32
 33static int nf_nat_ftp_fmt_cmd(struct nf_conn *ct, enum nf_ct_ftp_type type,
 34			      char *buffer, size_t buflen,
 35			      union nf_inet_addr *addr, u16 port)
 36{
 37	switch (type) {
 38	case NF_CT_FTP_PORT:
 39	case NF_CT_FTP_PASV:
 40		return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
 41				((unsigned char *)&addr->ip)[0],
 42				((unsigned char *)&addr->ip)[1],
 43				((unsigned char *)&addr->ip)[2],
 44				((unsigned char *)&addr->ip)[3],
 45				port >> 8,
 46				port & 0xFF);
 47	case NF_CT_FTP_EPRT:
 48		if (nf_ct_l3num(ct) == NFPROTO_IPV4)
 49			return snprintf(buffer, buflen, "|1|%pI4|%u|",
 50					&addr->ip, port);
 51		else
 52			return snprintf(buffer, buflen, "|2|%pI6|%u|",
 53					&addr->ip6, port);
 54	case NF_CT_FTP_EPSV:
 55		return snprintf(buffer, buflen, "|||%u|", port);
 56	}
 57
 58	return 0;
 59}
 60
 61/* So, this packet has hit the connection tracking matching code.
 62   Mangle it, and change the expectation to match the new version. */
 63static unsigned int nf_nat_ftp(struct sk_buff *skb,
 64			       enum ip_conntrack_info ctinfo,
 65			       enum nf_ct_ftp_type type,
 66			       unsigned int protoff,
 67			       unsigned int matchoff,
 68			       unsigned int matchlen,
 69			       struct nf_conntrack_expect *exp)
 70{
 71	union nf_inet_addr newaddr;
 72	u_int16_t port;
 73	int dir = CTINFO2DIR(ctinfo);
 74	struct nf_conn *ct = exp->master;
 75	char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
 76	unsigned int buflen;
 77
 78	pr_debug("type %i, off %u len %u\n", type, matchoff, matchlen);
 79
 80	/* Connection will come from wherever this packet goes, hence !dir */
 81	newaddr = ct->tuplehash[!dir].tuple.dst.u3;
 82	exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
 83	exp->dir = !dir;
 84
 85	/* When you see the packet, we need to NAT it the same as the
 86	 * this one. */
 87	exp->expectfn = nf_nat_follow_master;
 88
 89	port = nf_nat_exp_find_port(exp, ntohs(exp->saved_proto.tcp.port));
 90	if (port == 0) {
 91		nf_ct_helper_log(skb, exp->master, "all ports in use");
 92		return NF_DROP;
 93	}
 94
 95	buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
 96				    &newaddr, port);
 97	if (!buflen)
 98		goto out;
 99
100	pr_debug("calling nf_nat_mangle_tcp_packet\n");
101
102	if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
103				      matchlen, buffer, buflen))
104		goto out;
105
106	return NF_ACCEPT;
107
108out:
109	nf_ct_helper_log(skb, ct, "cannot mangle packet");
110	nf_ct_unexpect_related(exp);
111	return NF_DROP;
112}
113
114static void __exit nf_nat_ftp_fini(void)
115{
116	nf_nat_helper_unregister(&nat_helper_ftp);
117	RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
118	synchronize_rcu();
119}
120
121static int __init nf_nat_ftp_init(void)
122{
123	BUG_ON(nf_nat_ftp_hook != NULL);
124	nf_nat_helper_register(&nat_helper_ftp);
125	RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
126	return 0;
127}
128
129/* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
130static int warn_set(const char *val, const struct kernel_param *kp)
131{
132	pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
133	return 0;
134}
135module_param_call(ports, warn_set, NULL, NULL, 0);
136
137module_init(nf_nat_ftp_init);
138module_exit(nf_nat_ftp_fini);