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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  21
  22 #include <linux/module.h>
  23 #include <linux/moduleparam.h>
  24 #include <linux/netfilter.h>
  25 #include <linux/slab.h>
  26 #include <linux/in.h>
  27 #include <linux/tcp.h>
  28 #include <net/netfilter/nf_conntrack.h>
  29 #include <net/netfilter/nf_conntrack_helper.h>
  30 #include <net/netfilter/nf_conntrack_expect.h>
  31 #include <linux/netfilter/nf_conntrack_sane.h>
  32
  33 MODULE_LICENSE("GPL");
  34 MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
  35 MODULE_DESCRIPTION("SANE connection tracking helper");
  36 MODULE_ALIAS_NFCT_HELPER("sane");
  37
  38 static char *sane_buffer;
  39
  40 static DEFINE_SPINLOCK(nf_sane_lock);
  41
  42 #define MAX_PORTS 8
  43 static u_int16_t ports[MAX_PORTS];
  44 static unsigned int ports_c;
  45 module_param_array(ports, ushort, &ports_c, 0400);
  46
  47 struct sane_request {
  48         __be32 RPC_code;
  49 #define SANE_NET_START      7   /* RPC code */
  50
  51         __be32 handle;
  52 };
  53
  54 struct sane_reply_net_start {
  55         __be32 status;
  56 #define SANE_STATUS_SUCCESS 0
  57
  58         __be16 zero;
  59         __be16 port;
  60         /* other fields aren't interesting for conntrack */
  61 };
  62
  63 static int help(struct sk_buff *skb,
  64                 unsigned int protoff,
  65                 struct nf_conn *ct,
  66                 enum ip_conntrack_info ctinfo)
  67 {
  68         unsigned int dataoff, datalen;
  69         const struct tcphdr *th;
  70         struct tcphdr _tcph;
  71         void *sb_ptr;
  72         int ret = NF_ACCEPT;
  73         int dir = CTINFO2DIR(ctinfo);
  74         struct nf_ct_sane_master *ct_sane_info = nfct_help_data(ct);
  75         struct nf_conntrack_expect *exp;
  76         struct nf_conntrack_tuple *tuple;
  77         struct sane_request *req;
  78         struct sane_reply_net_start *reply;
  79
  80         /* Until there's been traffic both ways, don't look in packets. */
  81         if (ctinfo != IP_CT_ESTABLISHED &&
  82             ctinfo != IP_CT_ESTABLISHED_REPLY)
  83                 return NF_ACCEPT;
  84
  85         /* Not a full tcp header? */
  86         th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
  87         if (th == NULL)
  88                 return NF_ACCEPT;
  89
  90         /* No data? */
  91         dataoff = protoff + th->doff * 4;
  92         if (dataoff >= skb->len)
  93                 return NF_ACCEPT;
  94
  95         datalen = skb->len - dataoff;
  96
  97         spin_lock_bh(&nf_sane_lock);
  98         sb_ptr = skb_header_pointer(skb, dataoff, datalen, sane_buffer);
  99         BUG_ON(sb_ptr == NULL);
 100
 101         if (dir == IP_CT_DIR_ORIGINAL) {
 102                 if (datalen != sizeof(struct sane_request))
 103                         goto out;
 104
 105                 req = sb_ptr;
 106                 if (req->RPC_code != htonl(SANE_NET_START)) {
 107                         /* Not an interesting command */
 108                         ct_sane_info->state = SANE_STATE_NORMAL;
 109                         goto out;
 110                 }
 111
 112                 /* We're interested in the next reply */
 113                 ct_sane_info->state = SANE_STATE_START_REQUESTED;
 114                 goto out;
 115         }
 116
 117         /* Is it a reply to an uninteresting command? */
 118         if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
 119                 goto out;
 120
 121         /* It's a reply to SANE_NET_START. */
 122         ct_sane_info->state = SANE_STATE_NORMAL;
 123
 124         if (datalen < sizeof(struct sane_reply_net_start)) {
 125                 pr_debug("NET_START reply too short\n");
 126                 goto out;
 127         }
 128
 129         reply = sb_ptr;
 130         if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
 131                 /* saned refused the command */
 132                 pr_debug("unsuccessful SANE_STATUS = %u\n",
 133                          ntohl(reply->status));
 134                 goto out;
 135         }
 136
 137         /* Invalid saned reply? Ignore it. */
 138         if (reply->zero != 0)
 139                 goto out;
 140
 141         exp = nf_ct_expect_alloc(ct);
 142         if (exp == NULL) {
 143                 nf_ct_helper_log(skb, ct, "cannot alloc expectation");
 144                 ret = NF_DROP;
 145                 goto out;
 146         }
 147
 148         tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 149         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
 150                           &tuple->src.u3, &tuple->dst.u3,
 151                           IPPROTO_TCP, NULL, &reply->port);
 152
 153         pr_debug("expect: ");
 154         nf_ct_dump_tuple(&exp->tuple);
 155
 156         /* Can't expect this?  Best to drop packet now. */
 157         if (nf_ct_expect_related(exp) != 0) {
 158                 nf_ct_helper_log(skb, ct, "cannot add expectation");
 159                 ret = NF_DROP;
 160         }
 161
 162         nf_ct_expect_put(exp);
 163
 164 out:
 165         spin_unlock_bh(&nf_sane_lock);
 166         return ret;
 167 }
 168
 169 static struct nf_conntrack_helper sane[MAX_PORTS * 2] __read_mostly;
 170
 171 static const struct nf_conntrack_expect_policy sane_exp_policy = {
 172         .max_expected   = 1,
 173         .timeout        = 5 * 60,
 174 };
 175
 176 static void __exit nf_conntrack_sane_fini(void)
 177 {
 178         nf_conntrack_helpers_unregister(sane, ports_c * 2);
 179         kfree(sane_buffer);
 180 }
 181
 182 static int __init nf_conntrack_sane_init(void)
 183 {
 184         int i, ret = 0;
 185
 186         NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_sane_master));
 187
 188         sane_buffer = kmalloc(65536, GFP_KERNEL);
 189         if (!sane_buffer)
 190                 return -ENOMEM;
 191
 192         if (ports_c == 0)
 193                 ports[ports_c++] = SANE_PORT;
 194
 195         /* FIXME should be configurable whether IPv4 and IPv6 connections
 196                  are tracked or not - YK */
 197         for (i = 0; i < ports_c; i++) {
 198                 nf_ct_helper_init(&sane[2 * i], AF_INET, IPPROTO_TCP, "sane",
 199                                   SANE_PORT, ports[i], ports[i],
 200                                   &sane_exp_policy, 0, help, NULL,
 201                                   THIS_MODULE);
 202                 nf_ct_helper_init(&sane[2 * i + 1], AF_INET6, IPPROTO_TCP, "sane",
 203                                   SANE_PORT, ports[i], ports[i],
 204                                   &sane_exp_policy, 0, help, NULL,
 205                                   THIS_MODULE);
 206         }
 207
 208         ret = nf_conntrack_helpers_register(sane, ports_c * 2);
 209         if (ret < 0) {
 210                 pr_err("failed to register helpers\n");
 211                 kfree(sane_buffer);
 212                 return ret;
 213         }
 214
 215         return 0;
 216 }
 217
 218 module_init(nf_conntrack_sane_init);
 219 module_exit(nf_conntrack_sane_fini);