linux/net/netfilter/nf_conntrack_sane.c
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   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#include <linux/module.h>
  21#include <linux/moduleparam.h>
  22#include <linux/netfilter.h>
  23#include <linux/slab.h>
  24#include <linux/in.h>
  25#include <linux/tcp.h>
  26#include <net/netfilter/nf_conntrack.h>
  27#include <net/netfilter/nf_conntrack_helper.h>
  28#include <net/netfilter/nf_conntrack_expect.h>
  29#include <linux/netfilter/nf_conntrack_sane.h>
  30
  31MODULE_LICENSE("GPL");
  32MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
  33MODULE_DESCRIPTION("SANE connection tracking helper");
  34MODULE_ALIAS_NFCT_HELPER("sane");
  35
  36static char *sane_buffer;
  37
  38static DEFINE_SPINLOCK(nf_sane_lock);
  39
  40#define MAX_PORTS 8
  41static u_int16_t ports[MAX_PORTS];
  42static unsigned int ports_c;
  43module_param_array(ports, ushort, &ports_c, 0400);
  44
  45struct sane_request {
  46        __be32 RPC_code;
  47#define SANE_NET_START      7   /* RPC code */
  48
  49        __be32 handle;
  50};
  51
  52struct sane_reply_net_start {
  53        __be32 status;
  54#define SANE_STATUS_SUCCESS 0
  55
  56        __be16 zero;
  57        __be16 port;
  58        /* other fields aren't interesting for conntrack */
  59};
  60
  61static int help(struct sk_buff *skb,
  62                unsigned int protoff,
  63                struct nf_conn *ct,
  64                enum ip_conntrack_info ctinfo)
  65{
  66        unsigned int dataoff, datalen;
  67        const struct tcphdr *th;
  68        struct tcphdr _tcph;
  69        void *sb_ptr;
  70        int ret = NF_ACCEPT;
  71        int dir = CTINFO2DIR(ctinfo);
  72        struct nf_ct_sane_master *ct_sane_info = nfct_help_data(ct);
  73        struct nf_conntrack_expect *exp;
  74        struct nf_conntrack_tuple *tuple;
  75        struct sane_request *req;
  76        struct sane_reply_net_start *reply;
  77
  78        /* Until there's been traffic both ways, don't look in packets. */
  79        if (ctinfo != IP_CT_ESTABLISHED &&
  80            ctinfo != IP_CT_ESTABLISHED_REPLY)
  81                return NF_ACCEPT;
  82
  83        /* Not a full tcp header? */
  84        th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
  85        if (th == NULL)
  86                return NF_ACCEPT;
  87
  88        /* No data? */
  89        dataoff = protoff + th->doff * 4;
  90        if (dataoff >= skb->len)
  91                return NF_ACCEPT;
  92
  93        datalen = skb->len - dataoff;
  94
  95        spin_lock_bh(&nf_sane_lock);
  96        sb_ptr = skb_header_pointer(skb, dataoff, datalen, sane_buffer);
  97        BUG_ON(sb_ptr == NULL);
  98
  99        if (dir == IP_CT_DIR_ORIGINAL) {
 100                if (datalen != sizeof(struct sane_request))
 101                        goto out;
 102
 103                req = sb_ptr;
 104                if (req->RPC_code != htonl(SANE_NET_START)) {
 105                        /* Not an interesting command */
 106                        ct_sane_info->state = SANE_STATE_NORMAL;
 107                        goto out;
 108                }
 109
 110                /* We're interested in the next reply */
 111                ct_sane_info->state = SANE_STATE_START_REQUESTED;
 112                goto out;
 113        }
 114
 115        /* Is it a reply to an uninteresting command? */
 116        if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
 117                goto out;
 118
 119        /* It's a reply to SANE_NET_START. */
 120        ct_sane_info->state = SANE_STATE_NORMAL;
 121
 122        if (datalen < sizeof(struct sane_reply_net_start)) {
 123                pr_debug("nf_ct_sane: NET_START reply too short\n");
 124                goto out;
 125        }
 126
 127        reply = sb_ptr;
 128        if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
 129                /* saned refused the command */
 130                pr_debug("nf_ct_sane: unsuccessful SANE_STATUS = %u\n",
 131                         ntohl(reply->status));
 132                goto out;
 133        }
 134
 135        /* Invalid saned reply? Ignore it. */
 136        if (reply->zero != 0)
 137                goto out;
 138
 139        exp = nf_ct_expect_alloc(ct);
 140        if (exp == NULL) {
 141                nf_ct_helper_log(skb, ct, "cannot alloc expectation");
 142                ret = NF_DROP;
 143                goto out;
 144        }
 145
 146        tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 147        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
 148                          &tuple->src.u3, &tuple->dst.u3,
 149                          IPPROTO_TCP, NULL, &reply->port);
 150
 151        pr_debug("nf_ct_sane: expect: ");
 152        nf_ct_dump_tuple(&exp->tuple);
 153
 154        /* Can't expect this?  Best to drop packet now. */
 155        if (nf_ct_expect_related(exp) != 0) {
 156                nf_ct_helper_log(skb, ct, "cannot add expectation");
 157                ret = NF_DROP;
 158        }
 159
 160        nf_ct_expect_put(exp);
 161
 162out:
 163        spin_unlock_bh(&nf_sane_lock);
 164        return ret;
 165}
 166
 167static struct nf_conntrack_helper sane[MAX_PORTS][2] __read_mostly;
 168
 169static const struct nf_conntrack_expect_policy sane_exp_policy = {
 170        .max_expected   = 1,
 171        .timeout        = 5 * 60,
 172};
 173
 174/* don't make this __exit, since it's called from __init ! */
 175static void nf_conntrack_sane_fini(void)
 176{
 177        int i, j;
 178
 179        for (i = 0; i < ports_c; i++) {
 180                for (j = 0; j < 2; j++) {
 181                        pr_debug("nf_ct_sane: unregistering helper for pf: %d "
 182                                 "port: %d\n",
 183                                 sane[i][j].tuple.src.l3num, ports[i]);
 184                        nf_conntrack_helper_unregister(&sane[i][j]);
 185                }
 186        }
 187
 188        kfree(sane_buffer);
 189}
 190
 191static int __init nf_conntrack_sane_init(void)
 192{
 193        int i, j = -1, ret = 0;
 194
 195        sane_buffer = kmalloc(65536, GFP_KERNEL);
 196        if (!sane_buffer)
 197                return -ENOMEM;
 198
 199        if (ports_c == 0)
 200                ports[ports_c++] = SANE_PORT;
 201
 202        /* FIXME should be configurable whether IPv4 and IPv6 connections
 203                 are tracked or not - YK */
 204        for (i = 0; i < ports_c; i++) {
 205                sane[i][0].tuple.src.l3num = PF_INET;
 206                sane[i][1].tuple.src.l3num = PF_INET6;
 207                for (j = 0; j < 2; j++) {
 208                        sane[i][j].data_len = sizeof(struct nf_ct_sane_master);
 209                        sane[i][j].tuple.src.u.tcp.port = htons(ports[i]);
 210                        sane[i][j].tuple.dst.protonum = IPPROTO_TCP;
 211                        sane[i][j].expect_policy = &sane_exp_policy;
 212                        sane[i][j].me = THIS_MODULE;
 213                        sane[i][j].help = help;
 214                        if (ports[i] == SANE_PORT)
 215                                sprintf(sane[i][j].name, "sane");
 216                        else
 217                                sprintf(sane[i][j].name, "sane-%d", ports[i]);
 218
 219                        pr_debug("nf_ct_sane: registering helper for pf: %d "
 220                                 "port: %d\n",
 221                                 sane[i][j].tuple.src.l3num, ports[i]);
 222                        ret = nf_conntrack_helper_register(&sane[i][j]);
 223                        if (ret) {
 224                                printk(KERN_ERR "nf_ct_sane: failed to "
 225                                       "register helper for pf: %d port: %d\n",
 226                                        sane[i][j].tuple.src.l3num, ports[i]);
 227                                nf_conntrack_sane_fini();
 228                                return ret;
 229                        }
 230                }
 231        }
 232
 233        return 0;
 234}
 235
 236module_init(nf_conntrack_sane_init);
 237module_exit(nf_conntrack_sane_fini);
 238
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