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/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
  31 MODULE_LICENSE("GPL");
  32 MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
  33 MODULE_DESCRIPTION("SANE connection tracking helper");
  34 MODULE_ALIAS_NFCT_HELPER("sane");
  35
  36 static char *sane_buffer;
  37
  38 static DEFINE_SPINLOCK(nf_sane_lock);
  39
  40 #define MAX_PORTS 8
  41 static u_int16_t ports[MAX_PORTS];
  42 static unsigned int ports_c;
  43 module_param_array(ports, ushort, &ports_c, 0400);
  44
  45 struct sane_request {
  46         __be32 RPC_code;
  47 #define SANE_NET_START      7   /* RPC code */
  48
  49         __be32 handle;
  50 };
  51
  52 struct 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
  61 static 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
 162 out:
 163         spin_unlock_bh(&nf_sane_lock);
 164         return ret;
 165 }
 166
 167 static struct nf_conntrack_helper sane[MAX_PORTS][2] __read_mostly;
 168
 169 static 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 ! */
 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                         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
 191 static 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
 236 module_init(nf_conntrack_sane_init);
 237 module_exit(nf_conntrack_sane_fini);