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(buf: buffer, size: buflen, fmt: "%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(buf: buffer, size: buflen, fmt: "|1|%pI4|%u|",
50 &addr->ip, port);
51 else
52 return snprintf(buf: buffer, size: buflen, fmt: "|2|%pI6|%u|",
53 &addr->ip6, port);
54 case NF_CT_FTP_EPSV:
55 return snprintf(buf: buffer, size: buflen, fmt: "|||%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, ct: exp->master, fmt: "all ports in use");
92 return NF_DROP;
93 }
94
95 buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, buflen: sizeof(buffer),
96 addr: &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, match_offset: matchoff,
103 match_len: matchlen, rep_buffer: buffer, rep_len: buflen))
104 goto out;
105
106 return NF_ACCEPT;
107
108out:
109 nf_ct_helper_log(skb, ct, fmt: "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: &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: &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);
139