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/in.h>
  24#include <linux/tcp.h>
  25#include <net/netfilter/nf_conntrack.h>
  26#include <net/netfilter/nf_conntrack_helper.h>
  27#include <net/netfilter/nf_conntrack_expect.h>
  28#include <linux/netfilter/nf_conntrack_sane.h>
  29
  30MODULE_LICENSE("GPL");
  31MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
  32MODULE_DESCRIPTION("SANE connection tracking helper");
  33
  34static char *sane_buffer;
  35
  36static DEFINE_SPINLOCK(nf_sane_lock);
  37
  38#define MAX_PORTS 8
  39static u_int16_t ports[MAX_PORTS];
  40static unsigned int ports_c;
  41module_param_array(ports, ushort, &ports_c, 0400);
  42
  43struct sane_request {
  44        __be32 RPC_code;
  45#define SANE_NET_START      7   /* RPC code */
  46
  47        __be32 handle;
  48};
  49
  50struct sane_reply_net_start {
  51        __be32 status;
  52#define SANE_STATUS_SUCCESS 0
  53
  54        __be16 zero;
  55        __be16 port;
  56        /* other fields aren't interesting for conntrack */
  57};
  58
  59static int help(struct sk_buff *skb,
  60                unsigned int protoff,
  61                struct nf_conn *ct,
  62                enum ip_conntrack_info ctinfo)
  63{
  64        unsigned int dataoff, datalen;
  65        const struct tcphdr *th;
  66        struct tcphdr _tcph;
  67        void *sb_ptr;
  68        int ret = NF_ACCEPT;
  69        int dir = CTINFO2DIR(ctinfo);
  70        struct nf_ct_sane_master *ct_sane_info;
  71        struct nf_conntrack_expect *exp;
  72        struct nf_conntrack_tuple *tuple;
  73        struct sane_request *req;
  74        struct sane_reply_net_start *reply;
  75
  76        ct_sane_info = &nfct_help(ct)->help.ct_sane_info;
  77        /* Until there's been traffic both ways, don't look in packets. */
  78        if (ctinfo != IP_CT_ESTABLISHED &&
  79            ctinfo != IP_CT_ESTABLISHED+IP_CT_IS_REPLY)
  80                return NF_ACCEPT;
  81
  82        /* Not a full tcp header? */
  83        th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
  84        if (th == NULL)
  85                return NF_ACCEPT;
  86
  87        /* No data? */
  88        dataoff = protoff + th->doff * 4;
  89        if (dataoff >= skb->len)
  90                return NF_ACCEPT;
  91
  92        datalen = skb->len - dataoff;
  93
  94        spin_lock_bh(&nf_sane_lock);
  95        sb_ptr = skb_header_pointer(skb, dataoff, datalen, sane_buffer);
  96        BUG_ON(sb_ptr == NULL);
  97
  98        if (dir == IP_CT_DIR_ORIGINAL) {
  99                if (datalen != sizeof(struct sane_request))
 100                        goto out;
 101
 102                req = sb_ptr;
 103                if (req->RPC_code != htonl(SANE_NET_START)) {
 104                        /* Not an interesting command */
 105                        ct_sane_info->state = SANE_STATE_NORMAL;
 106                        goto out;
 107                }
 108
 109                /* We're interested in the next reply */
 110                ct_sane_info->state = SANE_STATE_START_REQUESTED;
 111                goto out;
 112        }
 113
 114        /* Is it a reply to an uninteresting command? */
 115        if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
 116                goto out;
 117
 118        /* It's a reply to SANE_NET_START. */
 119        ct_sane_info->state = SANE_STATE_NORMAL;
 120
 121        if (datalen < sizeof(struct sane_reply_net_start)) {
 122                pr_debug("nf_ct_sane: NET_START reply too short\n");
 123                goto out;
 124        }
 125
 126        reply = sb_ptr;
 127        if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
 128                /* saned refused the command */
 129                pr_debug("nf_ct_sane: unsuccessful SANE_STATUS = %u\n",
 130                         ntohl(reply->status));
 131                goto out;
 132        }
 133
 134        /* Invalid saned reply? Ignore it. */
 135        if (reply->zero != 0)
 136                goto out;
 137
 138        exp = nf_ct_expect_alloc(ct);
 139        if (exp == NULL) {
 140                ret = NF_DROP;
 141                goto out;
 142        }
 143
 144        tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 145        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
 146                          &tuple->src.u3, &tuple->dst.u3,
 147                          IPPROTO_TCP, NULL, &reply->port);
 148
 149        pr_debug("nf_ct_sane: expect: ");
 150        nf_ct_dump_tuple(&exp->tuple);
 151
 152        /* Can't expect this?  Best to drop packet now. */
 153        if (nf_ct_expect_related(exp) != 0)
 154                ret = NF_DROP;
 155
 156        nf_ct_expect_put(exp);
 157
 158out:
 159        spin_unlock_bh(&nf_sane_lock);
 160        return ret;
 161}
 162
 163static struct nf_conntrack_helper sane[MAX_PORTS][2] __read_mostly;
 164static char sane_names[MAX_PORTS][2][sizeof("sane-65535")] __read_mostly;
 165
 166static const struct nf_conntrack_expect_policy sane_exp_policy = {
 167        .max_expected   = 1,
 168        .timeout        = 5 * 60,
 169};
 170
 171/* don't make this __exit, since it's called from __init ! */
 172static void nf_conntrack_sane_fini(void)
 173{
 174        int i, j;
 175
 176        for (i = 0; i < ports_c; i++) {
 177                for (j = 0; j < 2; j++) {
 178                        pr_debug("nf_ct_sane: unregistering helper for pf: %d "
 179                                 "port: %d\n",
 180                                 sane[i][j].tuple.src.l3num, ports[i]);
 181                        nf_conntrack_helper_unregister(&sane[i][j]);
 182                }
 183        }
 184
 185        kfree(sane_buffer);
 186}
 187
 188static int __init nf_conntrack_sane_init(void)
 189{
 190        int i, j = -1, ret = 0;
 191        char *tmpname;
 192
 193        sane_buffer = kmalloc(65536, GFP_KERNEL);
 194        if (!sane_buffer)
 195                return -ENOMEM;
 196
 197        if (ports_c == 0)
 198                ports[ports_c++] = SANE_PORT;
 199
 200        /* FIXME should be configurable whether IPv4 and IPv6 connections
 201                 are tracked or not - YK */
 202        for (i = 0; i < ports_c; i++) {
 203                sane[i][0].tuple.src.l3num = PF_INET;
 204                sane[i][1].tuple.src.l3num = PF_INET6;
 205                for (j = 0; j < 2; j++) {
 206                        sane[i][j].tuple.src.u.tcp.port = htons(ports[i]);
 207                        sane[i][j].tuple.dst.protonum = IPPROTO_TCP;
 208                        sane[i][j].expect_policy = &sane_exp_policy;
 209                        sane[i][j].me = THIS_MODULE;
 210                        sane[i][j].help = help;
 211                        tmpname = &sane_names[i][j][0];
 212                        if (ports[i] == SANE_PORT)
 213                                sprintf(tmpname, "sane");
 214                        else
 215                                sprintf(tmpname, "sane-%d", ports[i]);
 216                        sane[i][j].name = tmpname;
 217
 218                        pr_debug("nf_ct_sane: registering helper for pf: %d "
 219                                 "port: %d\n",
 220                                 sane[i][j].tuple.src.l3num, ports[i]);
 221                        ret = nf_conntrack_helper_register(&sane[i][j]);
 222                        if (ret) {
 223                                printk(KERN_ERR "nf_ct_sane: failed to "
 224                                       "register helper for pf: %d port: %d\n",
 225                                        sane[i][j].tuple.src.l3num, ports[i]);
 226                                nf_conntrack_sane_fini();
 227                                return ret;
 228                        }
 229                }
 230        }
 231
 232        return 0;
 233}
 234
 235module_init(nf_conntrack_sane_init);
 236module_exit(nf_conntrack_sane_fini);
 237