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