nf_nat_ftp.c

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/* FTP extension for TCP NAT alteration. */

/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/inet.h>
#include <linux/tcp.h>
#include <linux/netfilter_ipv4.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_helper.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <linux/netfilter/nf_conntrack_ftp.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Rusty Russell <[email protected]>");
MODULE_DESCRIPTION("ftp NAT helper");
MODULE_ALIAS("ip_nat_ftp");

/* FIXME: Time out? --RR */

static int nf_nat_ftp_fmt_cmd(struct nf_conn *ct, enum nf_ct_ftp_type type,
                  char *buffer, size_t buflen,
                  union nf_inet_addr *addr, u16 port)
{
    switch (type) {
    case NF_CT_FTP_PORT:
    case NF_CT_FTP_PASV:
        return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
                ((unsigned char *)&addr->ip)[0],
                ((unsigned char *)&addr->ip)[1],
                ((unsigned char *)&addr->ip)[2],
                ((unsigned char *)&addr->ip)[3],
                port >> 8,
                port & 0xFF);
    case NF_CT_FTP_EPRT:
        if (nf_ct_l3num(ct) == NFPROTO_IPV4)
            return snprintf(buffer, buflen, "|1|%pI4|%u|",
                    &addr->ip, port);
        else
            return snprintf(buffer, buflen, "|2|%pI6|%u|",
                    &addr->ip6, port);
    case NF_CT_FTP_EPSV:
        return snprintf(buffer, buflen, "|||%u|", port);
    }

    return 0;
}

/* So, this packet has hit the connection tracking matching code.
   Mangle it, and change the expectation to match the new version. */
static unsigned int nf_nat_ftp(struct sk_buff *skb,
                   enum ip_conntrack_info ctinfo,
                   enum nf_ct_ftp_type type,
                   unsigned int protoff,
                   unsigned int matchoff,
                   unsigned int matchlen,
                   struct nf_conntrack_expect *exp)
{
    union nf_inet_addr newaddr;
    u_int16_t port;
    int dir = CTINFO2DIR(ctinfo);
    struct nf_conn *ct = exp->master;
    char buffer[sizeof("|1||65535|") + INET6_ADDRSTRLEN];
    unsigned int buflen;

    pr_debug("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen);

    /* Connection will come from wherever this packet goes, hence !dir */
    newaddr = ct->tuplehash[!dir].tuple.dst.u3;
    exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
    exp->dir = !dir;

    /* When you see the packet, we need to NAT it the same as the
     * this one. */
    exp->expectfn = nf_nat_follow_master;

    /* Try to get same port: if not, try to change it. */
    for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
        int ret;

        exp->tuple.dst.u.tcp.port = htons(port);
        ret = nf_ct_expect_related(exp);
        if (ret == 0)
            break;
        else if (ret != -EBUSY) {
            port = 0;
            break;
        }
    }

    if (port == 0)
        return NF_DROP;

    buflen = nf_nat_ftp_fmt_cmd(ct, type, buffer, sizeof(buffer),
                    &newaddr, port);
    if (!buflen)
        goto out;

    pr_debug("calling nf_nat_mangle_tcp_packet\n");

    if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
                      matchlen, buffer, buflen))
        goto out;

    return NF_ACCEPT;

out:
    nf_ct_unexpect_related(exp);
    return NF_DROP;
}

static void __exit nf_nat_ftp_fini(void)
{
    RCU_INIT_POINTER(nf_nat_ftp_hook, NULL);
    synchronize_rcu();
}

static int __init nf_nat_ftp_init(void)
{
    BUG_ON(nf_nat_ftp_hook != NULL);
    RCU_INIT_POINTER(nf_nat_ftp_hook, nf_nat_ftp);
    return 0;
}

/* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
static int warn_set(const char *val, struct kernel_param *kp)
{
    printk(KERN_INFO KBUILD_MODNAME
           ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
    return 0;
}
module_param_call(ports, warn_set, NULL, NULL, 0);

module_init(nf_nat_ftp_init);
module_exit(nf_nat_ftp_fini);