net/netfilter/nf_conntrack_sane.c

   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
  30 MODULE_LICENSE("GPL");
  31 MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
  32 MODULE_DESCRIPTION("SANE connection tracking helper");
  33
  34 static char *sane_buffer;
  35
  36 static DEFINE_SPINLOCK(nf_sane_lock);
  37
  38 #define MAX_PORTS 8
  39 static u_int16_t ports[MAX_PORTS];
  40 static unsigned int ports_c;
  41 module_param_array(ports, ushort, &ports_c, 0400);
  42
  43 struct sane_request {
  44         __be32 RPC_code;
  45 #define SANE_NET_START      7   /* RPC code */
  46
  47         __be32 handle;
  48 };
  49
  50 struct 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
  59 static 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         struct tcphdr _tcph, *th;
  66         char *sb_ptr;
  67         int ret = NF_ACCEPT;
  68         int dir = CTINFO2DIR(ctinfo);
  69         struct nf_ct_sane_master *ct_sane_info;
  70         struct nf_conntrack_expect *exp;
  71         struct nf_conntrack_tuple *tuple;
  72         struct sane_request *req;
  73         struct sane_reply_net_start *reply;
  74         int family = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.l3num;
  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 = (struct sane_request *)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 = (struct sane_reply_net_start *)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, family, &tuple->src.u3, &tuple->dst.u3,
 146                           IPPROTO_TCP, NULL, &reply->port);
 147
 148         pr_debug("nf_ct_sane: expect: ");
 149         NF_CT_DUMP_TUPLE(&exp->tuple);
 150
 151         /* Can't expect this?  Best to drop packet now. */
 152         if (nf_ct_expect_related(exp) != 0)
 153                 ret = NF_DROP;
 154
 155         nf_ct_expect_put(exp);
 156
 157 out:
 158         spin_unlock_bh(&nf_sane_lock);
 159         return ret;
 160 }
 161
 162 static struct nf_conntrack_helper sane[MAX_PORTS][2] __read_mostly;
 163 static char sane_names[MAX_PORTS][2][sizeof("sane-65535")] __read_mostly;
 164
 165 /* don't make this __exit, since it's called from __init ! */
 166 static void nf_conntrack_sane_fini(void)
 167 {
 168         int i, j;
 169
 170         for (i = 0; i < ports_c; i++) {
 171                 for (j = 0; j < 2; j++) {
 172                         pr_debug("nf_ct_sane: unregistering helper for pf: %d "
 173                                  "port: %d\n",
 174                                  sane[i][j].tuple.src.l3num, ports[i]);
 175                         nf_conntrack_helper_unregister(&sane[i][j]);
 176                 }
 177         }
 178
 179         kfree(sane_buffer);
 180 }
 181
 182 static int __init nf_conntrack_sane_init(void)
 183 {
 184         int i, j = -1, ret = 0;
 185         char *tmpname;
 186
 187         sane_buffer = kmalloc(65536, GFP_KERNEL);
 188         if (!sane_buffer)
 189                 return -ENOMEM;
 190
 191         if (ports_c == 0)
 192                 ports[ports_c++] = SANE_PORT;
 193
 194         /* FIXME should be configurable whether IPv4 and IPv6 connections
 195                  are tracked or not - YK */
 196         for (i = 0; i < ports_c; i++) {
 197                 sane[i][0].tuple.src.l3num = PF_INET;
 198                 sane[i][1].tuple.src.l3num = PF_INET6;
 199                 for (j = 0; j < 2; j++) {
 200                         sane[i][j].tuple.src.u.tcp.port = htons(ports[i]);
 201                         sane[i][j].tuple.dst.protonum = IPPROTO_TCP;
 202                         sane[i][j].max_expected = 1;
 203                         sane[i][j].timeout = 5 * 60;    /* 5 Minutes */
 204                         sane[i][j].me = THIS_MODULE;
 205                         sane[i][j].help = help;
 206                         tmpname = &sane_names[i][j][0];
 207                         if (ports[i] == SANE_PORT)
 208                                 sprintf(tmpname, "sane");
 209                         else
 210                                 sprintf(tmpname, "sane-%d", ports[i]);
 211                         sane[i][j].name = tmpname;
 212
 213                         pr_debug("nf_ct_sane: registering helper for pf: %d "
 214                                  "port: %d\n",
 215                                  sane[i][j].tuple.src.l3num, ports[i]);
 216                         ret = nf_conntrack_helper_register(&sane[i][j]);
 217                         if (ret) {
 218                                 printk(KERN_ERR "nf_ct_sane: failed to "
 219                                        "register helper for pf: %d port: %d\n",
 220                                         sane[i][j].tuple.src.l3num, ports[i]);
 221                                 nf_conntrack_sane_fini();
 222                                 return ret;
 223                         }
 224                 }
 225         }
 226
 227         return 0;
 228 }
 229
 230 module_init(nf_conntrack_sane_init);
 231 module_exit(nf_conntrack_sane_fini);