net/netfilter/nf_nat_ftp.c

   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
  23 MODULE_LICENSE("GPL");
  24 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  25 MODULE_DESCRIPTION("ftp NAT helper");
  26 MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
  27
  28 /* FIXME: Time out? --RR */
  29
  30 static struct nf_conntrack_nat_helper nat_helper_ftp =
  31         NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
  32
  33 static 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. */
  63 static 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);
  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
 121 out:
 122         nf_ct_helper_log(skb, ct, "cannot mangle packet");
 123         nf_ct_unexpect_related(exp);
 124         return NF_DROP;
 125 }
 126
 127 static 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
 134 static 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. */
 143 static 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 }
 148 module_param_call(ports, warn_set, NULL, NULL, 0);
 149
 150 module_init(nf_nat_ftp_init);
 151 module_exit(nf_nat_ftp_fini);