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 /* FIXME: Time out? --RR */
  29
  30 static int nf_nat_ftp_fmt_cmd(enum nf_ct_ftp_type type,
  31                               char *buffer, size_t buflen,
  32                               __be32 addr, u16 port)
  33 {
  34         switch (type) {
  35         case NF_CT_FTP_PORT:
  36         case NF_CT_FTP_PASV:
  37                 return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
  38                                 ((unsigned char *)&addr)[0],
  39                                 ((unsigned char *)&addr)[1],
  40                                 ((unsigned char *)&addr)[2],
  41                                 ((unsigned char *)&addr)[3],
  42                                 port >> 8,
  43                                 port & 0xFF);
  44         case NF_CT_FTP_EPRT:
  45                 return snprintf(buffer, buflen, "|1|%pI4|%u|", &addr, port);
  46         case NF_CT_FTP_EPSV:
  47                 return snprintf(buffer, buflen, "|||%u|", port);
  48         }
  49
  50         return 0;
  51 }
  52
  53 /* So, this packet has hit the connection tracking matching code.
  54    Mangle it, and change the expectation to match the new version. */
  55 static unsigned int nf_nat_ftp(struct sk_buff *skb,
  56                                enum ip_conntrack_info ctinfo,
  57                                enum nf_ct_ftp_type type,
  58                                unsigned int matchoff,
  59                                unsigned int matchlen,
  60                                struct nf_conntrack_expect *exp)
  61 {
  62         __be32 newip;
  63         u_int16_t port;
  64         int dir = CTINFO2DIR(ctinfo);
  65         struct nf_conn *ct = exp->master;
  66         char buffer[sizeof("|1|255.255.255.255|65535|")];
  67         unsigned int buflen;
  68
  69         pr_debug("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen);
  70
  71         /* Connection will come from wherever this packet goes, hence !dir */
  72         newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
  73         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  74         exp->dir = !dir;
  75
  76         /* When you see the packet, we need to NAT it the same as the
  77          * this one. */
  78         exp->expectfn = nf_nat_follow_master;
  79
  80         /* Try to get same port: if not, try to change it. */
  81         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  82                 int ret;
  83
  84                 exp->tuple.dst.u.tcp.port = htons(port);
  85                 ret = nf_ct_expect_related(exp);
  86                 if (ret == 0)
  87                         break;
  88                 else if (ret != -EBUSY) {
  89                         port = 0;
  90                         break;
  91                 }
  92         }
  93
  94         if (port == 0)
  95                 return NF_DROP;
  96
  97         buflen = nf_nat_ftp_fmt_cmd(type, buffer, sizeof(buffer), newip, port);
  98         if (!buflen)
  99                 goto out;
 100
 101         pr_debug("calling nf_nat_mangle_tcp_packet\n");
 102
 103         if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
 104                                       matchlen, buffer, buflen))
 105                 goto out;
 106
 107         return NF_ACCEPT;
 108
 109 out:
 110         nf_ct_unexpect_related(exp);
 111         return NF_DROP;
 112 }
 113
 114 static void __exit nf_nat_ftp_fini(void)
 115 {
 116         rcu_assign_pointer(nf_nat_ftp_hook, NULL);
 117         synchronize_rcu();
 118 }
 119
 120 static int __init nf_nat_ftp_init(void)
 121 {
 122         BUG_ON(nf_nat_ftp_hook != NULL);
 123         rcu_assign_pointer(nf_nat_ftp_hook, nf_nat_ftp);
 124         return 0;
 125 }
 126
 127 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 128 static int warn_set(const char *val, struct kernel_param *kp)
 129 {
 130         printk(KERN_INFO KBUILD_MODNAME
 131                ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 132         return 0;
 133 }
 134 module_param_call(ports, warn_set, NULL, NULL, 0);
 135
 136 module_init(nf_nat_ftp_init);
 137 module_exit(nf_nat_ftp_fini);