net/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/inet.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_conntrack_helper.h>
  19 #include <net/netfilter/nf_conntrack_expect.h>
  20 #include <linux/netfilter/nf_conntrack_ftp.h>
  21
  22 MODULE_LICENSE("GPL");
  23 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  24 MODULE_DESCRIPTION("ftp NAT helper");
  25 MODULE_ALIAS("ip_nat_ftp");
  26
  27 /* FIXME: Time out? --RR */
  28
  29 static int nf_nat_ftp_fmt_cmd(struct nf_conn *ct, enum nf_ct_ftp_type type,
  30                               char *buffer, size_t buflen,
  31                               union nf_inet_addr *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->ip)[0],
  38                                 ((unsigned char *)&addr->ip)[1],
  39                                 ((unsigned char *)&addr->ip)[2],
  40                                 ((unsigned char *)&addr->ip)[3],
  41                                 port >> 8,
  42                                 port & 0xFF);
  43         case NF_CT_FTP_EPRT:
  44                 if (nf_ct_l3num(ct) == NFPROTO_IPV4)
  45                         return snprintf(buffer, buflen, "|1|%pI4|%u|",
  46                                         &addr->ip, port);
  47                 else
  48                         return snprintf(buffer, buflen, "|2|%pI6|%u|",
  49                                         &addr->ip6, port);
  50         case NF_CT_FTP_EPSV:
  51                 return snprintf(buffer, buflen, "|||%u|", port);
  52         }
  53
  54         return 0;
  55 }
  56
  57 /* So, this packet has hit the connection tracking matching code.
  58    Mangle it, and change the expectation to match the new version. */
  59 static unsigned int nf_nat_ftp(struct sk_buff *skb,
  60                                enum ip_conntrack_info ctinfo,
  61                                enum nf_ct_ftp_type type,
  62                                unsigned int protoff,
  63                                unsigned int matchoff,
  64                                unsigned int matchlen,
  65                                struct nf_conntrack_expect *exp)
  66 {
  67         union nf_inet_addr newaddr;
  68         u_int16_t port;
  69         int dir = CTINFO2DIR(ctinfo);
  70         struct nf_conn *ct = exp->master;
  71         char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
  72         unsigned int buflen;
  73
  74         pr_debug("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen);
  75
  76         /* Connection will come from wherever this packet goes, hence !dir */
  77         newaddr = ct->tuplehash[!dir].tuple.dst.u3;
  78         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  79         exp->dir = !dir;
  80
  81         /* When you see the packet, we need to NAT it the same as the
  82          * this one. */
  83         exp->expectfn = nf_nat_follow_master;
  84
  85         /* Try to get same port: if not, try to change it. */
  86         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  87                 int ret;
  88
  89                 exp->tuple.dst.u.tcp.port = htons(port);
  90                 ret = nf_ct_expect_related(exp);
  91                 if (ret == 0)
  92                         break;
  93                 else if (ret != -EBUSY) {
  94                         port = 0;
  95                         break;
  96                 }
  97         }
  98
  99         if (port == 0)
 100                 return NF_DROP;
 101
 102         buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
 103                                     &newaddr, port);
 104         if (!buflen)
 105                 goto out;
 106
 107         pr_debug("calling nf_nat_mangle_tcp_packet\n");
 108
 109         if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
 110                                       matchlen, buffer, buflen))
 111                 goto out;
 112
 113         return NF_ACCEPT;
 114
 115 out:
 116         nf_ct_unexpect_related(exp);
 117         return NF_DROP;
 118 }
 119
 120 static void __exit nf_nat_ftp_fini(void)
 121 {
 122         RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
 123         synchronize_rcu();
 124 }
 125
 126 static int __init nf_nat_ftp_init(void)
 127 {
 128         BUG_ON(nf_nat_ftp_hook != NULL);
 129         RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
 130         return 0;
 131 }
 132
 133 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 134 static int warn_set(const char *val, struct kernel_param *kp)
 135 {
 136         printk(KERN_INFO KBUILD_MODNAME
 137                ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 138         return 0;
 139 }
 140 module_param_call(ports, warn_set, NULL, NULL, 0);
 141
 142 module_init(nf_nat_ftp_init);
 143 module_exit(nf_nat_ftp_fini);