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, 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; 120 121 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); 152