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