1 /* FTP extension for TCP NAT alteration. */
2
3 /* (C) 1999-2001 Paul `Rusty' Russell
4 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License version 2 as
8 * published by the Free Software Foundation.
9 */
10
11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
12
13 #include <linux/module.h>
14 #include <linux/moduleparam.h>
15 #include <linux/inet.h>
16 #include <linux/tcp.h>
17 #include <linux/netfilter_ipv4.h>
18 #include <net/netfilter/nf_nat.h>
19 #include <net/netfilter/nf_nat_helper.h>
20 #include <net/netfilter/nf_conntrack_helper.h>
21 #include <net/netfilter/nf_conntrack_expect.h>
22 #include <linux/netfilter/nf_conntrack_ftp.h>
23
24 MODULE_LICENSE("GPL");
25 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
26 MODULE_DESCRIPTION("ftp NAT helper");
27 MODULE_ALIAS("ip_nat_ftp");
28
29 /* FIXME: Time out? --RR */
30
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)31 static int nf_nat_ftp_fmt_cmd(struct nf_conn *ct, enum nf_ct_ftp_type type,
32 char *buffer, size_t buflen,
33 union nf_inet_addr *addr, u16 port)
34 {
35 switch (type) {
36 case NF_CT_FTP_PORT:
37 case NF_CT_FTP_PASV:
38 return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
39 ((unsigned char *)&addr->ip)[0],
40 ((unsigned char *)&addr->ip)[1],
41 ((unsigned char *)&addr->ip)[2],
42 ((unsigned char *)&addr->ip)[3],
43 port >> 8,
44 port & 0xFF);
45 case NF_CT_FTP_EPRT:
46 if (nf_ct_l3num(ct) == NFPROTO_IPV4)
47 return snprintf(buffer, buflen, "|1|%pI4|%u|",
48 &addr->ip, port);
49 else
50 return snprintf(buffer, buflen, "|2|%pI6|%u|",
51 &addr->ip6, port);
52 case NF_CT_FTP_EPSV:
53 return snprintf(buffer, buflen, "|||%u|", port);
54 }
55
56 return 0;
57 }
58
59 /* So, this packet has hit the connection tracking matching code.
60 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)61 static unsigned int nf_nat_ftp(struct sk_buff *skb,
62 enum ip_conntrack_info ctinfo,
63 enum nf_ct_ftp_type type,
64 unsigned int protoff,
65 unsigned int matchoff,
66 unsigned int matchlen,
67 struct nf_conntrack_expect *exp)
68 {
69 union nf_inet_addr newaddr;
70 u_int16_t port;
71 int dir = CTINFO2DIR(ctinfo);
72 struct nf_conn *ct = exp->master;
73 char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
74 unsigned int buflen;
75
76 pr_debug("type %i, off %u len %u\n", type, matchoff, matchlen);
77
78 /* Connection will come from wherever this packet goes, hence !dir */
79 newaddr = ct->tuplehash[!dir].tuple.dst.u3;
80 exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
81 exp->dir = !dir;
82
83 /* When you see the packet, we need to NAT it the same as the
84 * this one. */
85 exp->expectfn = nf_nat_follow_master;
86
87 /* Try to get same port: if not, try to change it. */
88 for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
89 int ret;
90
91 exp->tuple.dst.u.tcp.port = htons(port);
92 ret = nf_ct_expect_related(exp);
93 if (ret == 0)
94 break;
95 else if (ret != -EBUSY) {
96 port = 0;
97 break;
98 }
99 }
100
101 if (port == 0) {
102 nf_ct_helper_log(skb, ct, "all ports in use");
103 return NF_DROP;
104 }
105
106 buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
107 &newaddr, port);
108 if (!buflen)
109 goto out;
110
111 pr_debug("calling nf_nat_mangle_tcp_packet\n");
112
113 if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
114 matchlen, buffer, buflen))
115 goto out;
116
117 return NF_ACCEPT;
118
119 out:
120 nf_ct_helper_log(skb, ct, "cannot mangle packet");
121 nf_ct_unexpect_related(exp);
122 return NF_DROP;
123 }
124
nf_nat_ftp_fini(void)125 static void __exit nf_nat_ftp_fini(void)
126 {
127 RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
128 synchronize_rcu();
129 }
130
nf_nat_ftp_init(void)131 static int __init nf_nat_ftp_init(void)
132 {
133 BUG_ON(nf_nat_ftp_hook != NULL);
134 RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
135 return 0;
136 }
137
138 /* 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)139 static int warn_set(const char *val, const struct kernel_param *kp)
140 {
141 pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
142 return 0;
143 }
144 module_param_call(ports, warn_set, NULL, NULL, 0);
145
146 module_init(nf_nat_ftp_init);
147 module_exit(nf_nat_ftp_fini);
148
