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   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
  30 static int
  31 mangle_rfc959_packet(struct sk_buff *skb,
  32                      __be32 newip,
  33                      u_int16_t port,
  34                      unsigned int matchoff,
  35                      unsigned int matchlen,
  36                      struct nf_conn *ct,
  37                      enum ip_conntrack_info ctinfo)
  38 {
  39         char buffer[sizeof("nnn,nnn,nnn,nnn,nnn,nnn")];
  40
  41         sprintf(buffer, "%u,%u,%u,%u,%u,%u",
  42                 NIPQUAD(newip), port>>8, port&0xFF);
  43
  44         pr_debug("calling nf_nat_mangle_tcp_packet\n");
  45
  46         return nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
  47                                         matchlen, buffer, strlen(buffer));
  48 }
  49
  50 /* |1|132.235.1.2|6275| */
  51 static int
  52 mangle_eprt_packet(struct sk_buff *skb,
  53                    __be32 newip,
  54                    u_int16_t port,
  55                    unsigned int matchoff,
  56                    unsigned int matchlen,
  57                    struct nf_conn *ct,
  58                    enum ip_conntrack_info ctinfo)
  59 {
  60         char buffer[sizeof("|1|255.255.255.255|65535|")];
  61
  62         sprintf(buffer, "|1|%u.%u.%u.%u|%u|", NIPQUAD(newip), port);
  63
  64         pr_debug("calling nf_nat_mangle_tcp_packet\n");
  65
  66         return nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
  67                                         matchlen, buffer, strlen(buffer));
  68 }
  69
  70 /* |1|132.235.1.2|6275| */
  71 static int
  72 mangle_epsv_packet(struct sk_buff *skb,
  73                    __be32 newip,
  74                    u_int16_t port,
  75                    unsigned int matchoff,
  76                    unsigned int matchlen,
  77                    struct nf_conn *ct,
  78                    enum ip_conntrack_info ctinfo)
  79 {
  80         char buffer[sizeof("|||65535|")];
  81
  82         sprintf(buffer, "|||%u|", port);
  83
  84         pr_debug("calling nf_nat_mangle_tcp_packet\n");
  85
  86         return nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
  87                                         matchlen, buffer, strlen(buffer));
  88 }
  89
  90 static int (*mangle[])(struct sk_buff *, __be32, u_int16_t,
  91                        unsigned int, unsigned int, struct nf_conn *,
  92                        enum ip_conntrack_info)
  93 = {
  94         [NF_CT_FTP_PORT] = mangle_rfc959_packet,
  95         [NF_CT_FTP_PASV] = mangle_rfc959_packet,
  96         [NF_CT_FTP_EPRT] = mangle_eprt_packet,
  97         [NF_CT_FTP_EPSV] = mangle_epsv_packet
  98 };
  99
 100 /* So, this packet has hit the connection tracking matching code.
 101    Mangle it, and change the expectation to match the new version. */
 102 static unsigned int nf_nat_ftp(struct sk_buff *skb,
 103                                enum ip_conntrack_info ctinfo,
 104                                enum nf_ct_ftp_type type,
 105                                unsigned int matchoff,
 106                                unsigned int matchlen,
 107                                struct nf_conntrack_expect *exp)
 108 {
 109         __be32 newip;
 110         u_int16_t port;
 111         int dir = CTINFO2DIR(ctinfo);
 112         struct nf_conn *ct = exp->master;
 113
 114         pr_debug("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen);
 115
 116         /* Connection will come from wherever this packet goes, hence !dir */
 117         newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 118         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
 119         exp->dir = !dir;
 120
 121         /* When you see the packet, we need to NAT it the same as the
 122          * this one. */
 123         exp->expectfn = nf_nat_follow_master;
 124
 125         /* Try to get same port: if not, try to change it. */
 126         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
 127                 exp->tuple.dst.u.tcp.port = htons(port);
 128                 if (nf_ct_expect_related(exp) == 0)
 129                         break;
 130         }
 131
 132         if (port == 0)
 133                 return NF_DROP;
 134
 135         if (!mangle[type](skb, newip, port, matchoff, matchlen, ct, ctinfo)) {
 136                 nf_ct_unexpect_related(exp);
 137                 return NF_DROP;
 138         }
 139         return NF_ACCEPT;
 140 }
 141
 142 static void __exit nf_nat_ftp_fini(void)
 143 {
 144         rcu_assign_pointer(nf_nat_ftp_hook, NULL);
 145         synchronize_rcu();
 146 }
 147
 148 static int __init nf_nat_ftp_init(void)
 149 {
 150         BUG_ON(nf_nat_ftp_hook != NULL);
 151         rcu_assign_pointer(nf_nat_ftp_hook, nf_nat_ftp);
 152         return 0;
 153 }
 154
 155 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 156 static int warn_set(const char *val, struct kernel_param *kp)
 157 {
 158         printk(KERN_INFO KBUILD_MODNAME
 159                ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 160         return 0;
 161 }
 162 module_param_call(ports, warn_set, NULL, NULL, 0);
 163
 164 module_init(nf_nat_ftp_init);
 165 module_exit(nf_nat_ftp_fini);