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 #include <linux/module.h>
12 #include <linux/moduleparam.h>
13 #include <linux/ip.h>
14 #include <linux/tcp.h>
15 #include <linux/netfilter_ipv4.h>
16 #include <net/netfilter/nf_nat.h>
17 #include <net/netfilter/nf_nat_helper.h>
18 #include <net/netfilter/nf_nat_rule.h>
19 #include <net/netfilter/nf_conntrack_helper.h>
20 #include <net/netfilter/nf_conntrack_expect.h>
21 #include <linux/netfilter/nf_conntrack_ftp.h>
22
23 MODULE_LICENSE("GPL");
24 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
25 MODULE_DESCRIPTION("ftp NAT helper");
26 MODULE_ALIAS("ip_nat_ftp");
27
28 /* FIXME: Time out? --RR */
29
nf_nat_ftp_fmt_cmd(enum nf_ct_ftp_type type,char * buffer,size_t buflen,__be32 addr,u16 port)30 static int nf_nat_ftp_fmt_cmd(enum nf_ct_ftp_type type,
31 char *buffer, size_t buflen,
32 __be32 addr, u16 port)
33 {
34 switch (type) {
35 case NF_CT_FTP_PORT:
36 case NF_CT_FTP_PASV:
37 return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
38 ((unsigned char *)&addr)[0],
39 ((unsigned char *)&addr)[1],
40 ((unsigned char *)&addr)[2],
41 ((unsigned char *)&addr)[3],
42 port >> 8,
43 port & 0xFF);
44 case NF_CT_FTP_EPRT:
45 return snprintf(buffer, buflen, "|1|%pI4|%u|", &addr, port);
46 case NF_CT_FTP_EPSV:
47 return snprintf(buffer, buflen, "|||%u|", port);
48 }
49
50 return 0;
51 }
52
53 /* So, this packet has hit the connection tracking matching code.
54 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 matchoff,unsigned int matchlen,struct nf_conntrack_expect * exp)55 static unsigned int nf_nat_ftp(struct sk_buff *skb,
56 enum ip_conntrack_info ctinfo,
57 enum nf_ct_ftp_type type,
58 unsigned int matchoff,
59 unsigned int matchlen,
60 struct nf_conntrack_expect *exp)
61 {
62 __be32 newip;
63 u_int16_t port;
64 int dir = CTINFO2DIR(ctinfo);
65 struct nf_conn *ct = exp->master;
66 char buffer[sizeof("|1|255.255.255.255|65535|")];
67 unsigned int buflen;
68
69 pr_debug("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen);
70
71 /* Connection will come from wherever this packet goes, hence !dir */
72 newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
73 exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
74 exp->dir = !dir;
75
76 /* When you see the packet, we need to NAT it the same as the
77 * this one. */
78 exp->expectfn = nf_nat_follow_master;
79
80 /* Try to get same port: if not, try to change it. */
81 for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
82 int ret;
83
84 exp->tuple.dst.u.tcp.port = htons(port);
85 ret = nf_ct_expect_related(exp);
86 if (ret == 0)
87 break;
88 else if (ret != -EBUSY) {
89 port = 0;
90 break;
91 }
92 }
93
94 if (port == 0)
95 return NF_DROP;
96
97 buflen = nf_nat_ftp_fmt_cmd(type, buffer, sizeof(buffer), newip, port);
98 if (!buflen)
99 goto out;
100
101 pr_debug("calling nf_nat_mangle_tcp_packet\n");
102
103 if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
104 matchlen, buffer, buflen))
105 goto out;
106
107 return NF_ACCEPT;
108
109 out:
110 nf_ct_unexpect_related(exp);
111 return NF_DROP;
112 }
113
nf_nat_ftp_fini(void)114 static void __exit nf_nat_ftp_fini(void)
115 {
116 RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
117 synchronize_rcu();
118 }
119
nf_nat_ftp_init(void)120 static int __init nf_nat_ftp_init(void)
121 {
122 BUG_ON(nf_nat_ftp_hook != NULL);
123 RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
124 return 0;
125 }
126
127 /* Prior to 2.6.11, we had a ports param. No longer, but don't break users. */
warn_set(const char * val,struct kernel_param * kp)128 static int warn_set(const char *val, struct kernel_param *kp)
129 {
130 printk(KERN_INFO KBUILD_MODNAME
131 ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
132 return 0;
133 }
134 module_param_call(ports, warn_set, NULL, NULL, 0);
135
136 module_init(nf_nat_ftp_init);
137 module_exit(nf_nat_ftp_fini);
138