LXR linux/net/netfilter/nf_nat

   1// SPDX-License-Identifier: GPL-2.0-only
   2/* FTP extension for TCP NAT alteration. */
   3
   4/* (C) 1999-2001 Paul `Rusty' Russell
   5 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   6 */
   7
   8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   9
  10#include <linux/module.h>
  11#include <linux/moduleparam.h>
  12#include <linux/inet.h>
  13#include <linux/tcp.h>
  14#include <linux/netfilter_ipv4.h>
  15#include <net/netfilter/nf_nat.h>
  16#include <net/netfilter/nf_nat_helper.h>
  17#include <net/netfilter/nf_conntrack_helper.h>
  18#include <net/netfilter/nf_conntrack_expect.h>
  19#include <linux/netfilter/nf_conntrack_ftp.h>
  20
  21#define NAT_HELPER_NAME "ftp"
  22
  23MODULE_LICENSE("GPL");
  24MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  25MODULE_DESCRIPTION("ftp NAT helper");
  26MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
  27
  28/* FIXME: Time out? --RR */
  29
  30static struct nf_conntrack_nat_helper nat_helper_ftp =
  31        NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
  32
  33static int nf_nat_ftp_fmt_cmd(struct nf_conn *ct, enum nf_ct_ftp_type type,
  34                              char *buffer, size_t buflen,
  35                              union nf_inet_addr *addr, u16 port)
  36{
  37        switch (type) {
  38        case NF_CT_FTP_PORT:
  39        case NF_CT_FTP_PASV:
  40                return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
  41                                ((unsigned char *)&addr->ip)[0],
  42                                ((unsigned char *)&addr->ip)[1],
  43                                ((unsigned char *)&addr->ip)[2],
  44                                ((unsigned char *)&addr->ip)[3],
  45                                port >> 8,
  46                                port & 0xFF);
  47        case NF_CT_FTP_EPRT:
  48                if (nf_ct_l3num(ct) == NFPROTO_IPV4)
  49                        return snprintf(buffer, buflen, "|1|%pI4|%u|",
  50                                        &addr->ip, port);
  51                else
  52                        return snprintf(buffer, buflen, "|2|%pI6|%u|",
  53                                        &addr->ip6, port);
  54        case NF_CT_FTP_EPSV:
  55                return snprintf(buffer, buflen, "|||%u|", port);
  56        }
  57
  58        return 0;
  59}
  60
  61/* So, this packet has hit the connection tracking matching code.
  62   Mangle it, and change the expectation to match the new version. */
  63static unsigned int nf_nat_ftp(struct sk_buff *skb,
  64                               enum ip_conntrack_info ctinfo,
  65                               enum nf_ct_ftp_type type,
  66                               unsigned int protoff,
  67                               unsigned int matchoff,
  68                               unsigned int matchlen,
  69                               struct nf_conntrack_expect *exp)
  70{
  71        union nf_inet_addr newaddr;
  72        u_int16_t port;
  73        int dir = CTINFO2DIR(ctinfo);
  74        struct nf_conn *ct = exp->master;
  75        char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
  76        unsigned int buflen;
  77
  78        pr_debug("type %i, off %u len %u\n", type, matchoff, matchlen);
  79
  80        /* Connection will come from wherever this packet goes, hence !dir */
  81        newaddr = ct->tuplehash[!dir].tuple.dst.u3;
  82        exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  83        exp->dir = !dir;
  84
  85        /* When you see the packet, we need to NAT it the same as the
  86         * this one. */
  87        exp->expectfn = nf_nat_follow_master;
  88
  89        /* Try to get same port: if not, try to change it. */
  90        for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  91                int ret;
  92
  93                exp->tuple.dst.u.tcp.port = htons(port);
  94                ret = nf_ct_expect_related(exp, 0);
  95                if (ret == 0)
  96                        break;
  97                else if (ret != -EBUSY) {
  98                        port = 0;
  99                        break;
 100                }
 101        }
 102
 103        if (port == 0) {
 104                nf_ct_helper_log(skb, ct, "all ports in use");
 105                return NF_DROP;
 106        }
 107
 108        buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
 109                                    &newaddr, port);
 110        if (!buflen)
 111                goto out;
 112
 113        pr_debug("calling nf_nat_mangle_tcp_packet\n");
 114
 115        if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
 116                                      matchlen, buffer, buflen))
 117                goto out;
 118
 119        return NF_ACCEPT;
 120
 121out:
 122        nf_ct_helper_log(skb, ct, "cannot mangle packet");
 123        nf_ct_unexpect_related(exp);
 124        return NF_DROP;
 125}
 126
 127static void __exit nf_nat_ftp_fini(void)
 128{
 129        nf_nat_helper_unregister(&nat_helper_ftp);
 130        RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
 131        synchronize_rcu();
 132}
 133
 134static int __init nf_nat_ftp_init(void)
 135{
 136        BUG_ON(nf_nat_ftp_hook != NULL);
 137        nf_nat_helper_register(&nat_helper_ftp);
 138        RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
 139        return 0;
 140}
 141
 142/* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 143static int warn_set(const char *val, const struct kernel_param *kp)
 144{
 145        pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 146        return 0;
 147}
 148module_param_call(ports, warn_set, NULL, NULL, 0);
 149
 150module_init(nf_nat_ftp_init);
 151module_exit(nf_nat_ftp_fini);
 152