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
23 MODULE_LICENSE("GPL");
24 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
25 MODULE_DESCRIPTION("ftp NAT helper");
26 MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
27
28 /* FIXME: Time out? --RR */
29
30 static struct nf_conntrack_nat_helper nat_helper_ftp =
31 NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
32
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)33 static 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. */
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)63 static 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 /* Try to get same port: if not, try to change it. */
90 for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
91 int ret;
92
93 exp->tuple.dst.u.tcp.port = htons(port);
94 ret = nf_ct_expect_related(exp, 0);
95 if (ret == 0)
96 break;
97 else if (ret != -EBUSY) {
98 port = 0;
99 break;
100 }
101 }
102
103 if (port == 0) {
104 nf_ct_helper_log(skb, ct, "all ports in use");
105 return NF_DROP;
106 }
107
108 buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
109 &newaddr, port);
110 if (!buflen)
111 goto out;
112
113 pr_debug("calling nf_nat_mangle_tcp_packet\n");
114
115 if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
116 matchlen, buffer, buflen))
117 goto out;
118
119 return NF_ACCEPT;
120
121 out:
122 nf_ct_helper_log(skb, ct, "cannot mangle packet");
123 nf_ct_unexpect_related(exp);
124 return NF_DROP;
125 }
126
nf_nat_ftp_fini(void)127 static void __exit nf_nat_ftp_fini(void)
128 {
129 nf_nat_helper_unregister(&nat_helper_ftp);
130 RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
131 synchronize_rcu();
132 }
133
nf_nat_ftp_init(void)134 static int __init nf_nat_ftp_init(void)
135 {
136 BUG_ON(nf_nat_ftp_hook != NULL);
137 nf_nat_helper_register(&nat_helper_ftp);
138 RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
139 return 0;
140 }
141
142 /* Prior to 2.6.11, we had a ports param. No longer, but don't break users. */
warn_set(const char * val,const struct kernel_param * kp)143 static int warn_set(const char *val, const struct kernel_param *kp)
144 {
145 pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
146 return 0;
147 }
148 module_param_call(ports, warn_set, NULL, NULL, 0);
149
150 module_init(nf_nat_ftp_init);
151 module_exit(nf_nat_ftp_fini);
152