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         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
 158 out:
 159         spin_unlock_bh(&nf_sane_lock);
 160         return ret;
 161 }
 162
 163 static struct nf_conntrack_helper sane[MAX_PORTS][2] __read_mostly;
 164 static char sane_names[MAX_PORTS][2][sizeof("sane-65535")] __read_mostly;
 165
 166 static 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 ! */
 172 static 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
 188 static 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
 235 module_init(nf_conntrack_sane_init);
 236 module_exit(nf_conntrack_sane_fini);