LXR linux/net/netfilter/nf_conntrack

   1/* SANE connection tracking helper
   2 * (SANE = Scanner Access Now Easy)
   3 * For documentation about the SANE network protocol see
   4 * http://www.sane-project.org/html/doc015.html
   5 */
   6
   7/* Copyright (C) 2007 Red Hat, Inc.
   8 * Author: Michal Schmidt <mschmidt@redhat.com>
   9 * Based on the FTP conntrack helper (net/netfilter/nf_conntrack_ftp.c):
  10 *  (C) 1999-2001 Paul `Rusty' Russell
  11 *  (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
  12 *  (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
  13 *  (C) 2003 Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
  14 *
  15 * This program is free software; you can redistribute it and/or modify
  16 * it under the terms of the GNU General Public License version 2 as
  17 * published by the Free Software Foundation.
  18 */
  19
  20#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  21
  22#include <linux/module.h>
  23#include <linux/moduleparam.h>
  24#include <linux/netfilter.h>
  25#include <linux/slab.h>
  26#include <linux/in.h>
  27#include <linux/tcp.h>
  28#include <net/netfilter/nf_conntrack.h>
  29#include <net/netfilter/nf_conntrack_helper.h>
  30#include <net/netfilter/nf_conntrack_expect.h>
  31#include <linux/netfilter/nf_conntrack_sane.h>
  32
  33MODULE_LICENSE("GPL");
  34MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
  35MODULE_DESCRIPTION("SANE connection tracking helper");
  36MODULE_ALIAS_NFCT_HELPER("sane");
  37
  38static char *sane_buffer;
  39
  40static DEFINE_SPINLOCK(nf_sane_lock);
  41
  42#define MAX_PORTS 8
  43static u_int16_t ports[MAX_PORTS];
  44static unsigned int ports_c;
  45module_param_array(ports, ushort, &ports_c, 0400);
  46
  47struct sane_request {
  48        __be32 RPC_code;
  49#define SANE_NET_START      7   /* RPC code */
  50
  51        __be32 handle;
  52};
  53
  54struct sane_reply_net_start {
  55        __be32 status;
  56#define SANE_STATUS_SUCCESS 0
  57
  58        __be16 zero;
  59        __be16 port;
  60        /* other fields aren't interesting for conntrack */
  61};
  62
  63static int help(struct sk_buff *skb,
  64                unsigned int protoff,
  65                struct nf_conn *ct,
  66                enum ip_conntrack_info ctinfo)
  67{
  68        unsigned int dataoff, datalen;
  69        const struct tcphdr *th;
  70        struct tcphdr _tcph;
  71        void *sb_ptr;
  72        int ret = NF_ACCEPT;
  73        int dir = CTINFO2DIR(ctinfo);
  74        struct nf_ct_sane_master *ct_sane_info = nfct_help_data(ct);
  75        struct nf_conntrack_expect *exp;
  76        struct nf_conntrack_tuple *tuple;
  77        struct sane_request *req;
  78        struct sane_reply_net_start *reply;
  79
  80        /* Until there's been traffic both ways, don't look in packets. */
  81        if (ctinfo != IP_CT_ESTABLISHED &&
  82            ctinfo != IP_CT_ESTABLISHED_REPLY)
  83                return NF_ACCEPT;
  84
  85        /* Not a full tcp header? */
  86        th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
  87        if (th == NULL)
  88                return NF_ACCEPT;
  89
  90        /* No data? */
  91        dataoff = protoff + th->doff * 4;
  92        if (dataoff >= skb->len)
  93                return NF_ACCEPT;
  94
  95        datalen = skb->len - dataoff;
  96
  97        spin_lock_bh(&nf_sane_lock);
  98        sb_ptr = skb_header_pointer(skb, dataoff, datalen, sane_buffer);
  99        BUG_ON(sb_ptr == NULL);
 100
 101        if (dir == IP_CT_DIR_ORIGINAL) {
 102                if (datalen != sizeof(struct sane_request))
 103                        goto out;
 104
 105                req = sb_ptr;
 106                if (req->RPC_code != htonl(SANE_NET_START)) {
 107                        /* Not an interesting command */
 108                        ct_sane_info->state = SANE_STATE_NORMAL;
 109                        goto out;
 110                }
 111
 112                /* We're interested in the next reply */
 113                ct_sane_info->state = SANE_STATE_START_REQUESTED;
 114                goto out;
 115        }
 116
 117        /* Is it a reply to an uninteresting command? */
 118        if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
 119                goto out;
 120
 121        /* It's a reply to SANE_NET_START. */
 122        ct_sane_info->state = SANE_STATE_NORMAL;
 123
 124        if (datalen < sizeof(struct sane_reply_net_start)) {
 125                pr_debug("NET_START reply too short\n");
 126                goto out;
 127        }
 128
 129        reply = sb_ptr;
 130        if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
 131                /* saned refused the command */
 132                pr_debug("unsuccessful SANE_STATUS = %u\n",
 133                         ntohl(reply->status));
 134                goto out;
 135        }
 136
 137        /* Invalid saned reply? Ignore it. */
 138        if (reply->zero != 0)
 139                goto out;
 140
 141        exp = nf_ct_expect_alloc(ct);
 142        if (exp == NULL) {
 143                nf_ct_helper_log(skb, ct, "cannot alloc expectation");
 144                ret = NF_DROP;
 145                goto out;
 146        }
 147
 148        tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 149        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
 150                          &tuple->src.u3, &tuple->dst.u3,
 151                          IPPROTO_TCP, NULL, &reply->port);
 152
 153        pr_debug("expect: ");
 154        nf_ct_dump_tuple(&exp->tuple);
 155
 156        /* Can't expect this?  Best to drop packet now. */
 157        if (nf_ct_expect_related(exp) != 0) {
 158                nf_ct_helper_log(skb, ct, "cannot add expectation");
 159                ret = NF_DROP;
 160        }
 161
 162        nf_ct_expect_put(exp);
 163
 164out:
 165        spin_unlock_bh(&nf_sane_lock);
 166        return ret;
 167}
 168
 169static struct nf_conntrack_helper sane[MAX_PORTS * 2] __read_mostly;
 170
 171static const struct nf_conntrack_expect_policy sane_exp_policy = {
 172        .max_expected   = 1,
 173        .timeout        = 5 * 60,
 174};
 175
 176static void __exit nf_conntrack_sane_fini(void)
 177{
 178        nf_conntrack_helpers_unregister(sane, ports_c * 2);
 179        kfree(sane_buffer);
 180}
 181
 182static int __init nf_conntrack_sane_init(void)
 183{
 184        int i, ret = 0;
 185
 186        NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_sane_master));
 187
 188        sane_buffer = kmalloc(65536, GFP_KERNEL);
 189        if (!sane_buffer)
 190                return -ENOMEM;
 191
 192        if (ports_c == 0)
 193                ports[ports_c++] = SANE_PORT;
 194
 195        /* FIXME should be configurable whether IPv4 and IPv6 connections
 196                 are tracked or not - YK */
 197        for (i = 0; i < ports_c; i++) {
 198                nf_ct_helper_init(&sane[2 * i], AF_INET, IPPROTO_TCP, "sane",
 199                                  SANE_PORT, ports[i], ports[i],
 200                                  &sane_exp_policy, 0, help, NULL,
 201                                  THIS_MODULE);
 202                nf_ct_helper_init(&sane[2 * i + 1], AF_INET6, IPPROTO_TCP, "sane",
 203                                  SANE_PORT, ports[i], ports[i],
 204                                  &sane_exp_policy, 0, help, NULL,
 205                                  THIS_MODULE);
 206        }
 207
 208        ret = nf_conntrack_helpers_register(sane, ports_c * 2);
 209        if (ret < 0) {
 210                pr_err("failed to register helpers\n");
 211                kfree(sane_buffer);
 212                return ret;
 213        }
 214
 215        return 0;
 216}
 217
 218module_init(nf_conntrack_sane_init);
 219module_exit(nf_conntrack_sane_fini);
 220