nf_conntrack_tftp.c

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/* (C) 2001-2002 Magnus Boden <[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/in.h>
#include <linux/udp.h>
#include <linux/netfilter.h>

#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_tuple.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_conntrack_ecache.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <linux/netfilter/nf_conntrack_tftp.h>

MODULE_AUTHOR("Magnus Boden <[email protected]>");
MODULE_DESCRIPTION("TFTP connection tracking helper");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ip_conntrack_tftp");
MODULE_ALIAS_NFCT_HELPER("tftp");

#define MAX_PORTS 8
static unsigned short ports[MAX_PORTS];
static unsigned int ports_c;
module_param_array(ports, ushort, &ports_c, 0400);
MODULE_PARM_DESC(ports, "Port numbers of TFTP servers");

unsigned int (*nf_nat_tftp_hook)(struct sk_buff *skb,
                 enum ip_conntrack_info ctinfo,
                 struct nf_conntrack_expect *exp) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_tftp_hook);

static int tftp_help(struct sk_buff *skb,
             unsigned int protoff,
             struct nf_conn *ct,
             enum ip_conntrack_info ctinfo)
{
    const struct tftphdr *tfh;
    struct tftphdr _tftph;
    struct nf_conntrack_expect *exp;
    struct nf_conntrack_tuple *tuple;
    unsigned int ret = NF_ACCEPT;
    typeof(nf_nat_tftp_hook) nf_nat_tftp;

    tfh = skb_header_pointer(skb, protoff + sizeof(struct udphdr),
                 sizeof(_tftph), &_tftph);
    if (tfh == NULL)
        return NF_ACCEPT;

    switch (ntohs(tfh->opcode)) {
    case TFTP_OPCODE_READ:
    case TFTP_OPCODE_WRITE:
        /* RRQ and WRQ works the same way */
        nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
        nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);

        exp = nf_ct_expect_alloc(ct);
        if (exp == NULL)
            return NF_DROP;
        tuple = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
                  nf_ct_l3num(ct),
                  &tuple->src.u3, &tuple->dst.u3,
                  IPPROTO_UDP, NULL, &tuple->dst.u.udp.port);

        pr_debug("expect: ");
        nf_ct_dump_tuple(&exp->tuple);

        nf_nat_tftp = rcu_dereference(nf_nat_tftp_hook);
        if (nf_nat_tftp && ct->status & IPS_NAT_MASK)
            ret = nf_nat_tftp(skb, ctinfo, exp);
        else if (nf_ct_expect_related(exp) != 0)
            ret = NF_DROP;
        nf_ct_expect_put(exp);
        break;
    case TFTP_OPCODE_DATA:
    case TFTP_OPCODE_ACK:
        pr_debug("Data/ACK opcode\n");
        break;
    case TFTP_OPCODE_ERROR:
        pr_debug("Error opcode\n");
        break;
    default:
        pr_debug("Unknown opcode\n");
    }
    return ret;
}

static struct nf_conntrack_helper tftp[MAX_PORTS][2] __read_mostly;

static const struct nf_conntrack_expect_policy tftp_exp_policy = {
    .max_expected   = 1,
    .timeout    = 5 * 60,
};

static void nf_conntrack_tftp_fini(void)
{
    int i, j;

    for (i = 0; i < ports_c; i++) {
        for (j = 0; j < 2; j++)
            nf_conntrack_helper_unregister(&tftp[i][j]);
    }
}

static int __init nf_conntrack_tftp_init(void)
{
    int i, j, ret;

    if (ports_c == 0)
        ports[ports_c++] = TFTP_PORT;

    for (i = 0; i < ports_c; i++) {
        memset(&tftp[i], 0, sizeof(tftp[i]));

        tftp[i][0].tuple.src.l3num = AF_INET;
        tftp[i][1].tuple.src.l3num = AF_INET6;
        for (j = 0; j < 2; j++) {
            tftp[i][j].tuple.dst.protonum = IPPROTO_UDP;
            tftp[i][j].tuple.src.u.udp.port = htons(ports[i]);
            tftp[i][j].expect_policy = &tftp_exp_policy;
            tftp[i][j].me = THIS_MODULE;
            tftp[i][j].help = tftp_help;

            if (ports[i] == TFTP_PORT)
                sprintf(tftp[i][j].name, "tftp");
            else
                sprintf(tftp[i][j].name, "tftp-%u", i);

            ret = nf_conntrack_helper_register(&tftp[i][j]);
            if (ret) {
                printk(KERN_ERR "nf_ct_tftp: failed to register"
                       " helper for pf: %u port: %u\n",
                    tftp[i][j].tuple.src.l3num, ports[i]);
                nf_conntrack_tftp_fini();
                return ret;
            }
        }
    }
    return 0;
}

module_init(nf_conntrack_tftp_init);
module_exit(nf_conntrack_tftp_fini);