linux/net/netfilter/nf_nat_ftp.c
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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/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
  22MODULE_LICENSE("GPL");
  23MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  24MODULE_DESCRIPTION("ftp NAT helper");
  25MODULE_ALIAS("ip_nat_ftp");
  26
  27/* FIXME: Time out? --RR */
  28
  29static 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. */
  59static 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
 115out:
 116        nf_ct_unexpect_related(exp);
 117        return NF_DROP;
 118}
 119
 120static void __exit nf_nat_ftp_fini(void)
 121{
 122        RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
 123        synchronize_rcu();
 124}
 125
 126static 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. */
 134static 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}
 140module_param_call(ports, warn_set, NULL, NULL, 0);
 141
 142module_init(nf_nat_ftp_init);
 143module_exit(nf_nat_ftp_fini);
 144
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