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 #if 0
  44 #define DEBUGP printk
  45 #else
  46 #define DEBUGP(format, args...)
  47 #endif
  48
  49 struct sane_request {
  50         __be32 RPC_code;
  51 #define SANE_NET_START      7   /* RPC code */
  52
  53         __be32 handle;
  54 };
  55
  56 struct sane_reply_net_start {
  57         __be32 status;
  58 #define SANE_STATUS_SUCCESS 0
  59
  60         __be16 zero;
  61         __be16 port;
  62         /* other fields aren't interesting for conntrack */
  63 };
  64
  65 static int help(struct sk_buff **pskb,
  66                 unsigned int protoff,
  67                 struct nf_conn *ct,
  68                 enum ip_conntrack_info ctinfo)
  69 {
  70         unsigned int dataoff, datalen;
  71         struct tcphdr _tcph, *th;
  72         char *sb_ptr;
  73         int ret = NF_ACCEPT;
  74         int dir = CTINFO2DIR(ctinfo);
  75         struct nf_ct_sane_master *ct_sane_info;
  76         struct nf_conntrack_expect *exp;
  77         struct nf_conntrack_tuple *tuple;
  78         struct sane_request *req;
  79         struct sane_reply_net_start *reply;
  80         int family = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.l3num;
  81
  82         ct_sane_info = &nfct_help(ct)->help.ct_sane_info;
  83         /* Until there's been traffic both ways, don't look in packets. */
  84         if (ctinfo != IP_CT_ESTABLISHED &&
  85             ctinfo != IP_CT_ESTABLISHED+IP_CT_IS_REPLY)
  86                 return NF_ACCEPT;
  87
  88         /* Not a full tcp header? */
  89         th = skb_header_pointer(*pskb, protoff, sizeof(_tcph), &_tcph);
  90         if (th == NULL)
  91                 return NF_ACCEPT;
  92
  93         /* No data? */
  94         dataoff = protoff + th->doff * 4;
  95         if (dataoff >= (*pskb)->len)
  96                 return NF_ACCEPT;
  97
  98         datalen = (*pskb)->len - dataoff;
  99
 100         spin_lock_bh(&nf_sane_lock);
 101         sb_ptr = skb_header_pointer(*pskb, dataoff, datalen, sane_buffer);
 102         BUG_ON(sb_ptr == NULL);
 103
 104         if (dir == IP_CT_DIR_ORIGINAL) {
 105                 if (datalen != sizeof(struct sane_request))
 106                         goto out;
 107
 108                 req = (struct sane_request *)sb_ptr;
 109                 if (req->RPC_code != htonl(SANE_NET_START)) {
 110                         /* Not an interesting command */
 111                         ct_sane_info->state = SANE_STATE_NORMAL;
 112                         goto out;
 113                 }
 114
 115                 /* We're interested in the next reply */
 116                 ct_sane_info->state = SANE_STATE_START_REQUESTED;
 117                 goto out;
 118         }
 119
 120         /* Is it a reply to an uninteresting command? */
 121         if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
 122                 goto out;
 123
 124         /* It's a reply to SANE_NET_START. */
 125         ct_sane_info->state = SANE_STATE_NORMAL;
 126
 127         if (datalen < sizeof(struct sane_reply_net_start)) {
 128                 DEBUGP("nf_ct_sane: NET_START reply too short\n");
 129                 goto out;
 130         }
 131
 132         reply = (struct sane_reply_net_start *)sb_ptr;
 133         if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
 134                 /* saned refused the command */
 135                 DEBUGP("nf_ct_sane: unsuccessful SANE_STATUS = %u\n",
 136                         ntohl(reply->status));
 137                 goto out;
 138         }
 139
 140         /* Invalid saned reply? Ignore it. */
 141         if (reply->zero != 0)
 142                 goto out;
 143
 144         exp = nf_conntrack_expect_alloc(ct);
 145         if (exp == NULL) {
 146                 ret = NF_DROP;
 147                 goto out;
 148         }
 149
 150         tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 151         nf_conntrack_expect_init(exp, family,
 152                                  &tuple->src.u3, &tuple->dst.u3,
 153                                  IPPROTO_TCP,
 154                                  NULL, &reply->port);
 155
 156         DEBUGP("nf_ct_sane: expect: ");
 157         NF_CT_DUMP_TUPLE(&exp->tuple);
 158         NF_CT_DUMP_TUPLE(&exp->mask);
 159
 160         /* Can't expect this?  Best to drop packet now. */
 161         if (nf_conntrack_expect_related(exp) != 0)
 162                 ret = NF_DROP;
 163
 164         nf_conntrack_expect_put(exp);
 165
 166 out:
 167         spin_unlock_bh(&nf_sane_lock);
 168         return ret;
 169 }
 170
 171 static struct nf_conntrack_helper sane[MAX_PORTS][2];
 172 static char sane_names[MAX_PORTS][2][sizeof("sane-65535")];
 173
 174 /* don't make this __exit, since it's called from __init ! */
 175 static 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                         DEBUGP("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
 191 static int __init nf_conntrack_sane_init(void)
 192 {
 193         int i, j = -1, ret = 0;
 194         char *tmpname;
 195
 196         sane_buffer = kmalloc(65536, GFP_KERNEL);
 197         if (!sane_buffer)
 198                 return -ENOMEM;
 199
 200         if (ports_c == 0)
 201                 ports[ports_c++] = SANE_PORT;
 202
 203         /* FIXME should be configurable whether IPv4 and IPv6 connections
 204                  are tracked or not - YK */
 205         for (i = 0; i < ports_c; i++) {
 206                 sane[i][0].tuple.src.l3num = PF_INET;
 207                 sane[i][1].tuple.src.l3num = PF_INET6;
 208                 for (j = 0; j < 2; j++) {
 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].mask.src.u.tcp.port = 0xFFFF;
 212                         sane[i][j].mask.dst.protonum = 0xFF;
 213                         sane[i][j].max_expected = 1;
 214                         sane[i][j].timeout = 5 * 60;    /* 5 Minutes */
 215                         sane[i][j].me = THIS_MODULE;
 216                         sane[i][j].help = help;
 217                         tmpname = &sane_names[i][j][0];
 218                         if (ports[i] == SANE_PORT)
 219                                 sprintf(tmpname, "sane");
 220                         else
 221                                 sprintf(tmpname, "sane-%d", ports[i]);
 222                         sane[i][j].name = tmpname;
 223
 224                         DEBUGP("nf_ct_sane: registering helper for pf: %d "
 225                                "port: %d\n",
 226                                 sane[i][j].tuple.src.l3num, ports[i]);
 227                         ret = nf_conntrack_helper_register(&sane[i][j]);
 228                         if (ret) {
 229                                 printk(KERN_ERR "nf_ct_sane: failed to "
 230                                        "register helper for pf: %d port: %d\n",
 231                                         sane[i][j].tuple.src.l3num, ports[i]);
 232                                 nf_conntrack_sane_fini();
 233                                 return ret;
 234                         }
 235                 }
 236         }
 237
 238         return 0;
 239 }
 240
 241 module_init(nf_conntrack_sane_init);
 242 module_exit(nf_conntrack_sane_fini);