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/inet.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_conntrack_helper.h> 19 #include <net/netfilter/nf_conntrack_expect.h> 20 #include <linux/netfilter/nf_conntrack_ftp.h> 21 22 MODULE_LICENSE("GPL"); 23 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>"); 24 MODULE_DESCRIPTION("ftp NAT helper"); 25 MODULE_ALIAS("ip_nat_ftp"); 26 27 /* FIXME: Time out? --RR */ 28 29 static int nf_nat_ftp_fmt_cmd(struct nf_conn *ct, enum nf_ct_ftp_type type, 30 char *buffer, size_t buflen, 31 union nf_inet_addr *addr, u16 port) 32 { 33 switch (type) { 34 case NF_CT_FTP_PORT: 35 case NF_CT_FTP_PASV: 36 return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u", 37 ((unsigned char *)&addr->ip)[0], 38 ((unsigned char *)&addr->ip)[1], 39 ((unsigned char *)&addr->ip)[2], 40 ((unsigned char *)&addr->ip)[3], 41 port >> 8, 42 port & 0xFF); 43 case NF_CT_FTP_EPRT: 44 if (nf_ct_l3num(ct) == NFPROTO_IPV4) 45 return snprintf(buffer, buflen, "|1|%pI4|%u|", 46 &addr->ip, port); 47 else 48 return snprintf(buffer, buflen, "|2|%pI6|%u|", 49 &addr->ip6, port); 50 case NF_CT_FTP_EPSV: 51 return snprintf(buffer, buflen, "|||%u|", port); 52 } 53 54 return 0; 55 } 56 57 /* So, this packet has hit the connection tracking matching code. 58 Mangle it, and change the expectation to match the new version. */ 59 static unsigned int nf_nat_ftp(struct sk_buff *skb, 60 enum ip_conntrack_info ctinfo, 61 enum nf_ct_ftp_type type, 62 unsigned int protoff, 63 unsigned int matchoff, 64 unsigned int matchlen, 65 struct nf_conntrack_expect *exp) 66 { 67 union nf_inet_addr newaddr; 68 u_int16_t port; 69 int dir = CTINFO2DIR(ctinfo); 70 struct nf_conn *ct = exp->master; 71 char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN]; 72 unsigned int buflen; 73 74 pr_debug("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen); 75 76 /* Connection will come from wherever this packet goes, hence !dir */ 77 newaddr = ct->tuplehash[!dir].tuple.dst.u3; 78 exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port; 79 exp->dir = !dir; 80 81 /* When you see the packet, we need to NAT it the same as the 82 * this one. */ 83 exp->expectfn = nf_nat_follow_master; 84 85 /* Try to get same port: if not, try to change it. */ 86 for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) { 87 int ret; 88 89 exp->tuple.dst.u.tcp.port = htons(port); 90 ret = nf_ct_expect_related(exp); 91 if (ret == 0) 92 break; 93 else if (ret != -EBUSY) { 94 port = 0; 95 break; 96 } 97 } 98 99 if (port == 0) { 100 nf_ct_helper_log(skb, ct, "all ports in use"); 101 return NF_DROP; 102 } 103 104 buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer), 105 &newaddr, port); 106 if (!buflen) 107 goto out; 108 109 pr_debug("calling nf_nat_mangle_tcp_packet\n"); 110 111 if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff, 112 matchlen, buffer, buflen)) 113 goto out; 114 115 return NF_ACCEPT; 116 117 out: 118 nf_ct_helper_log(skb, ct, "cannot mangle packet"); 119 nf_ct_unexpect_related(exp); 120 return NF_DROP; 121 } 122 123 static void __exit nf_nat_ftp_fini(void) 124 { 125 RCU_INIT_POINTER(nf_nat_ftp_hook, NULL); 126 synchronize_rcu(); 127 } 128 129 static int __init nf_nat_ftp_init(void) 130 { 131 BUG_ON(nf_nat_ftp_hook != NULL); 132 RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp); 133 return 0; 134 } 135 136 /* Prior to 2.6.11, we had a ports param. No longer, but don't break users. */ 137 static int warn_set(const char *val, struct kernel_param *kp) 138 { 139 printk(KERN_INFO KBUILD_MODNAME 140 ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n"); 141 return 0; 142 } 143 module_param_call(ports, warn_set, NULL, NULL, 0); 144 145 module_init(nf_nat_ftp_init); 146 module_exit(nf_nat_ftp_fini); 147