// SPDX-License-Identifier: GPL-2.0-only
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/* FTP extension for TCP NAT alteration. */
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/* (C) 1999-2001 Paul `Rusty' Russell
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* (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/moduleparam.h>
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#include <linux/inet.h>
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#include <linux/tcp.h>
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#include <linux/netfilter_ipv4.h>
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#include <net/netfilter/nf_nat.h>
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#include <net/netfilter/nf_nat_helper.h>
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#include <net/netfilter/nf_conntrack_helper.h>
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#include <net/netfilter/nf_conntrack_expect.h>
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#include <linux/netfilter/nf_conntrack_ftp.h>
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#define NAT_HELPER_NAME "ftp"
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
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MODULE_DESCRIPTION("ftp NAT helper");
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MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
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/* FIXME: Time out? --RR */
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static struct nf_conntrack_nat_helper nat_helper_ftp =
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NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
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static int nf_nat_ftp_fmt_cmd(struct nf_conn *ct, enum nf_ct_ftp_type type,
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char *buffer, size_t buflen,
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union nf_inet_addr *addr, u16 port)
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{
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switch (type) {
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case NF_CT_FTP_PORT:
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case NF_CT_FTP_PASV:
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return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
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((unsigned char *)&addr->ip)[0],
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((unsigned char *)&addr->ip)[1],
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((unsigned char *)&addr->ip)[2],
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((unsigned char *)&addr->ip)[3],
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port >> 8,
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port & 0xFF);
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case NF_CT_FTP_EPRT:
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if (nf_ct_l3num(ct) == NFPROTO_IPV4)
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return snprintf(buffer, buflen, "|1|%pI4|%u|",
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&addr->ip, port);
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else
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return snprintf(buffer, buflen, "|2|%pI6|%u|",
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&addr->ip6, port);
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case NF_CT_FTP_EPSV:
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return snprintf(buffer, buflen, "|||%u|", port);
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}
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return 0;
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}
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/* So, this packet has hit the connection tracking matching code.
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Mangle it, and change the expectation to match the new version. */
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static unsigned int nf_nat_ftp(struct sk_buff *skb,
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enum ip_conntrack_info ctinfo,
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enum nf_ct_ftp_type type,
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unsigned int protoff,
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unsigned int matchoff,
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unsigned int matchlen,
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struct nf_conntrack_expect *exp)
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{
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union nf_inet_addr newaddr;
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u_int16_t port;
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int dir = CTINFO2DIR(ctinfo);
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struct nf_conn *ct = exp->master;
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char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
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unsigned int buflen;
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pr_debug("type %i, off %u len %u\n", type, matchoff, matchlen);
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/* Connection will come from wherever this packet goes, hence !dir */
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newaddr = ct->tuplehash[!dir].tuple.dst.u3;
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exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
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exp->dir = !dir;
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/* When you see the packet, we need to NAT it the same as the
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* this one. */
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exp->expectfn = nf_nat_follow_master;
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/* Try to get same port: if not, try to change it. */
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for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
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int ret;
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exp->tuple.dst.u.tcp.port = htons(port);
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ret = nf_ct_expect_related(exp, 0);
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if (ret == 0)
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break;
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else if (ret != -EBUSY) {
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port = 0;
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break;
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}
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}
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if (port == 0) {
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nf_ct_helper_log(skb, ct, "all ports in use");
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return NF_DROP;
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}
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buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
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&newaddr, port);
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if (!buflen)
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goto out;
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pr_debug("calling nf_nat_mangle_tcp_packet\n");
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if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
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matchlen, buffer, buflen))
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goto out;
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return NF_ACCEPT;
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out:
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nf_ct_helper_log(skb, ct, "cannot mangle packet");
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nf_ct_unexpect_related(exp);
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return NF_DROP;
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}
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static void __exit nf_nat_ftp_fini(void)
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{
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nf_nat_helper_unregister(&nat_helper_ftp);
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RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
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synchronize_rcu();
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}
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static int __init nf_nat_ftp_init(void)
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{
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BUG_ON(nf_nat_ftp_hook != NULL);
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nf_nat_helper_register(&nat_helper_ftp);
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RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
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return 0;
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}
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/* Prior to 2.6.11, we had a ports param. No longer, but don't break users. */
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static int warn_set(const char *val, const struct kernel_param *kp)
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{
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pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
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return 0;
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}
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module_param_call(ports, warn_set, NULL, NULL, 0);
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module_init(nf_nat_ftp_init);
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module_exit(nf_nat_ftp_fini);
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