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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  12
  13 #include <linux/module.h>
  14 #include <linux/moduleparam.h>
  15 #include <linux/inet.h>
  16 #include <linux/tcp.h>
  17 #include <linux/netfilter_ipv4.h>
  18 #include <net/netfilter/nf_nat.h>
  19 #include <net/netfilter/nf_nat_helper.h>
  20 #include <net/netfilter/nf_conntrack_helper.h>
  21 #include <net/netfilter/nf_conntrack_expect.h>
  22 #include <linux/netfilter/nf_conntrack_ftp.h>
  23
  24 #define NAT_HELPER_NAME "ftp"
  25
  26 MODULE_LICENSE("GPL");
  27 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  28 MODULE_DESCRIPTION("ftp NAT helper");
  29 MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
  30
  31 /* FIXME: Time out? --RR */
  32
  33 static struct nf_conntrack_nat_helper nat_helper_ftp =
  34         NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
  35
  36 static int nf_nat_ftp_fmt_cmd(struct nf_conn *ct, enum nf_ct_ftp_type type,
  37                               char *buffer, size_t buflen,
  38                               union nf_inet_addr *addr, u16 port)
  39 {
  40         switch (type) {
  41         case NF_CT_FTP_PORT:
  42         case NF_CT_FTP_PASV:
  43                 return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
  44                                 ((unsigned char *)&addr->ip)[0],
  45                                 ((unsigned char *)&addr->ip)[1],
  46                                 ((unsigned char *)&addr->ip)[2],
  47                                 ((unsigned char *)&addr->ip)[3],
  48                                 port >> 8,
  49                                 port & 0xFF);
  50         case NF_CT_FTP_EPRT:
  51                 if (nf_ct_l3num(ct) == NFPROTO_IPV4)
  52                         return snprintf(buffer, buflen, "|1|%pI4|%u|",
  53                                         &addr->ip, port);
  54                 else
  55                         return snprintf(buffer, buflen, "|2|%pI6|%u|",
  56                                         &addr->ip6, port);
  57         case NF_CT_FTP_EPSV:
  58                 return snprintf(buffer, buflen, "|||%u|", port);
  59         }
  60
  61         return 0;
  62 }
  63
  64 /* So, this packet has hit the connection tracking matching code.
  65    Mangle it, and change the expectation to match the new version. */
  66 static unsigned int nf_nat_ftp(struct sk_buff *skb,
  67                                enum ip_conntrack_info ctinfo,
  68                                enum nf_ct_ftp_type type,
  69                                unsigned int protoff,
  70                                unsigned int matchoff,
  71                                unsigned int matchlen,
  72                                struct nf_conntrack_expect *exp)
  73 {
  74         union nf_inet_addr newaddr;
  75         u_int16_t port;
  76         int dir = CTINFO2DIR(ctinfo);
  77         struct nf_conn *ct = exp->master;
  78         char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
  79         unsigned int buflen;
  80
  81         pr_debug("type %i, off %u len %u\n", type, matchoff, matchlen);
  82
  83         /* Connection will come from wherever this packet goes, hence !dir */
  84         newaddr = ct->tuplehash[!dir].tuple.dst.u3;
  85         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  86         exp->dir = !dir;
  87
  88         /* When you see the packet, we need to NAT it the same as the
  89          * this one. */
  90         exp->expectfn = nf_nat_follow_master;
  91
  92         /* Try to get same port: if not, try to change it. */
  93         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  94                 int ret;
  95
  96                 exp->tuple.dst.u.tcp.port = htons(port);
  97                 ret = nf_ct_expect_related(exp);
  98                 if (ret == 0)
  99                         break;
 100                 else if (ret != -EBUSY) {
 101                         port = 0;
 102                         break;
 103                 }
 104         }
 105
 106         if (port == 0) {
 107                 nf_ct_helper_log(skb, ct, "all ports in use");
 108                 return NF_DROP;
 109         }
 110
 111         buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
 112                                     &newaddr, port);
 113         if (!buflen)
 114                 goto out;
 115
 116         pr_debug("calling nf_nat_mangle_tcp_packet\n");
 117
 118         if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
 119                                       matchlen, buffer, buflen))
 120                 goto out;
 121
 122         return NF_ACCEPT;
 123
 124 out:
 125         nf_ct_helper_log(skb, ct, "cannot mangle packet");
 126         nf_ct_unexpect_related(exp);
 127         return NF_DROP;
 128 }
 129
 130 static void __exit nf_nat_ftp_fini(void)
 131 {
 132         nf_nat_helper_unregister(&nat_helper_ftp);
 133         RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
 134         synchronize_rcu();
 135 }
 136
 137 static int __init nf_nat_ftp_init(void)
 138 {
 139         BUG_ON(nf_nat_ftp_hook != NULL);
 140         nf_nat_helper_register(&nat_helper_ftp);
 141         RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
 142         return 0;
 143 }
 144
 145 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 146 static int warn_set(const char *val, const struct kernel_param *kp)
 147 {
 148         pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 149         return 0;
 150 }
 151 module_param_call(ports, warn_set, NULL, NULL, 0);
 152
 153 module_init(nf_nat_ftp_init);
 154 module_exit(nf_nat_ftp_fini);