release/src-rt-6.x.4708/linux/linux-2.6.36/net/ipv4/netfilter/nf_nat_ftp.c

   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
  29 static 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. */
  54 static 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
 101 out:
 102         nf_ct_unexpect_related(exp);
 103         return NF_DROP;
 104 }
 105
 106 static void __exit nf_nat_ftp_fini(void)
 107 {
 108         rcu_assign_pointer(nf_nat_ftp_hook, NULL);
 109         synchronize_rcu();
 110 }
 111
 112 static 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. */
 120 static 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 }
 126 module_param_call(ports, warn_set, NULL, NULL, 0);
 127
 128 module_init(nf_nat_ftp_init);
 129 module_exit(nf_nat_ftp_fini);