net/ipv4/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 #include <linux/module.h>
  12 #include <linux/moduleparam.h>
  13 #include <linux/ip.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_nat_rule.h>
  19 #include <net/netfilter/nf_conntrack_helper.h>
  20 #include <net/netfilter/nf_conntrack_expect.h>
  21 #include <linux/netfilter/nf_conntrack_ftp.h>
  22
  23 MODULE_LICENSE("GPL");
  24 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  25 MODULE_DESCRIPTION("ftp NAT helper");
  26 MODULE_ALIAS("ip_nat_ftp");
  27
  28 #if 0
  29 #define DEBUGP printk
  30 #else
  31 #define DEBUGP(format, args...)
  32 #endif
  33
  34 /* FIXME: Time out? --RR */
  35
  36 static int
  37 mangle_rfc959_packet(struct sk_buff **pskb,
  38                      __be32 newip,
  39                      u_int16_t port,
  40                      unsigned int matchoff,
  41                      unsigned int matchlen,
  42                      struct nf_conn *ct,
  43                      enum ip_conntrack_info ctinfo,
  44                      u32 *seq)
  45 {
  46         char buffer[sizeof("nnn,nnn,nnn,nnn,nnn,nnn")];
  47
  48         sprintf(buffer, "%u,%u,%u,%u,%u,%u",
  49                 NIPQUAD(newip), port>>8, port&0xFF);
  50
  51         DEBUGP("calling nf_nat_mangle_tcp_packet\n");
  52
  53         *seq += strlen(buffer) - matchlen;
  54         return nf_nat_mangle_tcp_packet(pskb, ct, ctinfo, matchoff,
  55                                         matchlen, buffer, strlen(buffer));
  56 }
  57
  58 /* |1|132.235.1.2|6275| */
  59 static int
  60 mangle_eprt_packet(struct sk_buff **pskb,
  61                    __be32 newip,
  62                    u_int16_t port,
  63                    unsigned int matchoff,
  64                    unsigned int matchlen,
  65                    struct nf_conn *ct,
  66                    enum ip_conntrack_info ctinfo,
  67                    u32 *seq)
  68 {
  69         char buffer[sizeof("|1|255.255.255.255|65535|")];
  70
  71         sprintf(buffer, "|1|%u.%u.%u.%u|%u|", NIPQUAD(newip), port);
  72
  73         DEBUGP("calling nf_nat_mangle_tcp_packet\n");
  74
  75         *seq += strlen(buffer) - matchlen;
  76         return nf_nat_mangle_tcp_packet(pskb, ct, ctinfo, matchoff,
  77                                         matchlen, buffer, strlen(buffer));
  78 }
  79
  80 /* |1|132.235.1.2|6275| */
  81 static int
  82 mangle_epsv_packet(struct sk_buff **pskb,
  83                    __be32 newip,
  84                    u_int16_t port,
  85                    unsigned int matchoff,
  86                    unsigned int matchlen,
  87                    struct nf_conn *ct,
  88                    enum ip_conntrack_info ctinfo,
  89                    u32 *seq)
  90 {
  91         char buffer[sizeof("|||65535|")];
  92
  93         sprintf(buffer, "|||%u|", port);
  94
  95         DEBUGP("calling nf_nat_mangle_tcp_packet\n");
  96
  97         *seq += strlen(buffer) - matchlen;
  98         return nf_nat_mangle_tcp_packet(pskb, ct, ctinfo, matchoff,
  99                                         matchlen, buffer, strlen(buffer));
 100 }
 101
 102 static int (*mangle[])(struct sk_buff **, __be32, u_int16_t,
 103                        unsigned int, unsigned int, struct nf_conn *,
 104                        enum ip_conntrack_info, u32 *seq)
 105 = {
 106         [NF_CT_FTP_PORT] = mangle_rfc959_packet,
 107         [NF_CT_FTP_PASV] = mangle_rfc959_packet,
 108         [NF_CT_FTP_EPRT] = mangle_eprt_packet,
 109         [NF_CT_FTP_EPSV] = mangle_epsv_packet
 110 };
 111
 112 /* So, this packet has hit the connection tracking matching code.
 113    Mangle it, and change the expectation to match the new version. */
 114 static unsigned int nf_nat_ftp(struct sk_buff **pskb,
 115                                enum ip_conntrack_info ctinfo,
 116                                enum nf_ct_ftp_type type,
 117                                unsigned int matchoff,
 118                                unsigned int matchlen,
 119                                struct nf_conntrack_expect *exp,
 120                                u32 *seq)
 121 {
 122         __be32 newip;
 123         u_int16_t port;
 124         int dir = CTINFO2DIR(ctinfo);
 125         struct nf_conn *ct = exp->master;
 126
 127         DEBUGP("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen);
 128
 129         /* Connection will come from wherever this packet goes, hence !dir */
 130         newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 131         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
 132         exp->dir = !dir;
 133
 134         /* When you see the packet, we need to NAT it the same as the
 135          * this one. */
 136         exp->expectfn = nf_nat_follow_master;
 137
 138         /* Try to get same port: if not, try to change it. */
 139         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
 140                 exp->tuple.dst.u.tcp.port = htons(port);
 141                 if (nf_conntrack_expect_related(exp) == 0)
 142                         break;
 143         }
 144
 145         if (port == 0)
 146                 return NF_DROP;
 147
 148         if (!mangle[type](pskb, newip, port, matchoff, matchlen, ct, ctinfo,
 149                           seq)) {
 150                 nf_conntrack_unexpect_related(exp);
 151                 return NF_DROP;
 152         }
 153         return NF_ACCEPT;
 154 }
 155
 156 static void __exit nf_nat_ftp_fini(void)
 157 {
 158         rcu_assign_pointer(nf_nat_ftp_hook, NULL);
 159         synchronize_rcu();
 160 }
 161
 162 static int __init nf_nat_ftp_init(void)
 163 {
 164         BUG_ON(rcu_dereference(nf_nat_ftp_hook));
 165         rcu_assign_pointer(nf_nat_ftp_hook, nf_nat_ftp);
 166         return 0;
 167 }
 168
 169 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 170 static int warn_set(const char *val, struct kernel_param *kp)
 171 {
 172         printk(KERN_INFO KBUILD_MODNAME
 173                ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 174         return 0;
 175 }
 176 module_param_call(ports, warn_set, NULL, NULL, 0);
 177
 178 module_init(nf_nat_ftp_init);
 179 module_exit(nf_nat_ftp_fini);