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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 #if 0
  29 #define DEBUGP printk
  30 #else
  31 #define DEBUGP(format, args...)
  32 #endif
  33
  34 /* FIXME: Time out? --RR */
  35
  36 static int
  37 mangle_rfc959_packet(struct sk_buff **pskb,
  38                      __be32 newip,
  39                      u_int16_t port,
  40                      unsigned int matchoff,
  41                      unsigned int matchlen,
  42                      struct nf_conn *ct,
  43                      enum ip_conntrack_info ctinfo)
  44 {
  45         char buffer[sizeof("nnn,nnn,nnn,nnn,nnn,nnn")];
  46
  47         sprintf(buffer, "%u,%u,%u,%u,%u,%u",
  48                 NIPQUAD(newip), port>>8, port&0xFF);
  49
  50         DEBUGP("calling nf_nat_mangle_tcp_packet\n");
  51
  52         return nf_nat_mangle_tcp_packet(pskb, ct, ctinfo, matchoff,
  53                                         matchlen, buffer, strlen(buffer));
  54 }
  55
  56 /* |1|132.235.1.2|6275| */
  57 static int
  58 mangle_eprt_packet(struct sk_buff **pskb,
  59                    __be32 newip,
  60                    u_int16_t port,
  61                    unsigned int matchoff,
  62                    unsigned int matchlen,
  63                    struct nf_conn *ct,
  64                    enum ip_conntrack_info ctinfo)
  65 {
  66         char buffer[sizeof("|1|255.255.255.255|65535|")];
  67
  68         sprintf(buffer, "|1|%u.%u.%u.%u|%u|", NIPQUAD(newip), port);
  69
  70         DEBUGP("calling nf_nat_mangle_tcp_packet\n");
  71
  72         return nf_nat_mangle_tcp_packet(pskb, ct, ctinfo, matchoff,
  73                                         matchlen, buffer, strlen(buffer));
  74 }
  75
  76 /* |1|132.235.1.2|6275| */
  77 static int
  78 mangle_epsv_packet(struct sk_buff **pskb,
  79                    __be32 newip,
  80                    u_int16_t port,
  81                    unsigned int matchoff,
  82                    unsigned int matchlen,
  83                    struct nf_conn *ct,
  84                    enum ip_conntrack_info ctinfo)
  85 {
  86         char buffer[sizeof("|||65535|")];
  87
  88         sprintf(buffer, "|||%u|", port);
  89
  90         DEBUGP("calling nf_nat_mangle_tcp_packet\n");
  91
  92         return nf_nat_mangle_tcp_packet(pskb, ct, ctinfo, matchoff,
  93                                         matchlen, buffer, strlen(buffer));
  94 }
  95
  96 static int (*mangle[])(struct sk_buff **, __be32, u_int16_t,
  97                        unsigned int, unsigned int, struct nf_conn *,
  98                        enum ip_conntrack_info)
  99 = {
 100         [NF_CT_FTP_PORT] = mangle_rfc959_packet,
 101         [NF_CT_FTP_PASV] = mangle_rfc959_packet,
 102         [NF_CT_FTP_EPRT] = mangle_eprt_packet,
 103         [NF_CT_FTP_EPSV] = mangle_epsv_packet
 104 };
 105
 106 /* So, this packet has hit the connection tracking matching code.
 107    Mangle it, and change the expectation to match the new version. */
 108 static unsigned int nf_nat_ftp(struct sk_buff **pskb,
 109                                enum ip_conntrack_info ctinfo,
 110                                enum nf_ct_ftp_type type,
 111                                unsigned int matchoff,
 112                                unsigned int matchlen,
 113                                struct nf_conntrack_expect *exp)
 114 {
 115         __be32 newip;
 116         u_int16_t port;
 117         int dir = CTINFO2DIR(ctinfo);
 118         struct nf_conn *ct = exp->master;
 119
 120         DEBUGP("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen);
 121
 122         /* Connection will come from wherever this packet goes, hence !dir */
 123         newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 124         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
 125         exp->dir = !dir;
 126
 127         /* When you see the packet, we need to NAT it the same as the
 128          * this one. */
 129         exp->expectfn = nf_nat_follow_master;
 130
 131         /* Try to get same port: if not, try to change it. */
 132         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
 133                 exp->tuple.dst.u.tcp.port = htons(port);
 134                 if (nf_ct_expect_related(exp) == 0)
 135                         break;
 136         }
 137
 138         if (port == 0)
 139                 return NF_DROP;
 140
 141         if (!mangle[type](pskb, newip, port, matchoff, matchlen, ct, ctinfo)) {
 142                 nf_ct_unexpect_related(exp);
 143                 return NF_DROP;
 144         }
 145         return NF_ACCEPT;
 146 }
 147
 148 static void __exit nf_nat_ftp_fini(void)
 149 {
 150         rcu_assign_pointer(nf_nat_ftp_hook, NULL);
 151         synchronize_rcu();
 152 }
 153
 154 static int __init nf_nat_ftp_init(void)
 155 {
 156         BUG_ON(rcu_dereference(nf_nat_ftp_hook));
 157         rcu_assign_pointer(nf_nat_ftp_hook, nf_nat_ftp);
 158         return 0;
 159 }
 160
 161 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 162 static int warn_set(const char *val, struct kernel_param *kp)
 163 {
 164         printk(KERN_INFO KBUILD_MODNAME
 165                ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 166         return 0;
 167 }
 168 module_param_call(ports, warn_set, NULL, NULL, 0);
 169
 170 module_init(nf_nat_ftp_init);
 171 module_exit(nf_nat_ftp_fini);