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;
  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         ct_sane_info = &nfct_help(ct)->help.ct_sane_info;
  79         /* Until there's been traffic both ways, don't look in packets. */
  80         if (ctinfo != IP_CT_ESTABLISHED &&
  81             ctinfo != IP_CT_ESTABLISHED_REPLY)
  82                 return NF_ACCEPT;
  83
  84         /* Not a full tcp header? */
  85         th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
  86         if (th == NULL)
  87                 return NF_ACCEPT;
  88
  89         /* No data? */
  90         dataoff = protoff + th->doff * 4;
  91         if (dataoff >= skb->len)
  92                 return NF_ACCEPT;
  93
  94         datalen = skb->len - dataoff;
  95
  96         spin_lock_bh(&nf_sane_lock);
  97         sb_ptr = skb_header_pointer(skb, dataoff, datalen, sane_buffer);
  98         BUG_ON(sb_ptr == NULL);
  99
 100         if (dir == IP_CT_DIR_ORIGINAL) {
 101                 if (datalen != sizeof(struct sane_request))
 102                         goto out;
 103
 104                 req = sb_ptr;
 105                 if (req->RPC_code != htonl(SANE_NET_START)) {
 106                         /* Not an interesting command */
 107                         ct_sane_info->state = SANE_STATE_NORMAL;
 108                         goto out;
 109                 }
 110
 111                 /* We're interested in the next reply */
 112                 ct_sane_info->state = SANE_STATE_START_REQUESTED;
 113                 goto out;
 114         }
 115
 116         /* Is it a reply to an uninteresting command? */
 117         if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
 118                 goto out;
 119
 120         /* It's a reply to SANE_NET_START. */
 121         ct_sane_info->state = SANE_STATE_NORMAL;
 122
 123         if (datalen < sizeof(struct sane_reply_net_start)) {
 124                 pr_debug("nf_ct_sane: NET_START reply too short\n");
 125                 goto out;
 126         }
 127
 128         reply = sb_ptr;
 129         if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
 130                 /* saned refused the command */
 131                 pr_debug("nf_ct_sane: unsuccessful SANE_STATUS = %u\n",
 132                          ntohl(reply->status));
 133                 goto out;
 134         }
 135
 136         /* Invalid saned reply? Ignore it. */
 137         if (reply->zero != 0)
 138                 goto out;
 139
 140         exp = nf_ct_expect_alloc(ct);
 141         if (exp == NULL) {
 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                 ret = NF_DROP;
 157
 158         nf_ct_expect_put(exp);
 159
 160 out:
 161         spin_unlock_bh(&nf_sane_lock);
 162         return ret;
 163 }
 164
 165 static struct nf_conntrack_helper sane[MAX_PORTS][2] __read_mostly;
 166
 167 static const struct nf_conntrack_expect_policy sane_exp_policy = {
 168         .max_expected   = 1,
 169         .timeout        = 5 * 60,
 170 };
 171
 172 /* don't make this __exit, since it's called from __init ! */
 173 static void nf_conntrack_sane_fini(void)
 174 {
 175         int i, j;
 176
 177         for (i = 0; i < ports_c; i++) {
 178                 for (j = 0; j < 2; j++) {
 179                         pr_debug("nf_ct_sane: unregistering helper for pf: %d "
 180                                  "port: %d\n",
 181                                  sane[i][j].tuple.src.l3num, ports[i]);
 182                         nf_conntrack_helper_unregister(&sane[i][j]);
 183                 }
 184         }
 185
 186         kfree(sane_buffer);
 187 }
 188
 189 static int __init nf_conntrack_sane_init(void)
 190 {
 191         int i, j = -1, ret = 0;
 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                         if (ports[i] == SANE_PORT)
 212                                 sprintf(sane[i][j].name, "sane");
 213                         else
 214                                 sprintf(sane[i][j].name, "sane-%d", ports[i]);
 215
 216                         pr_debug("nf_ct_sane: registering helper for pf: %d "
 217                                  "port: %d\n",
 218                                  sane[i][j].tuple.src.l3num, ports[i]);
 219                         ret = nf_conntrack_helper_register(&sane[i][j]);
 220                         if (ret) {
 221                                 printk(KERN_ERR "nf_ct_sane: failed to "
 222                                        "register helper for pf: %d port: %d\n",
 223                                         sane[i][j].tuple.src.l3num, ports[i]);
 224                                 nf_conntrack_sane_fini();
 225                                 return ret;
 226                         }
 227                 }
 228         }
 229
 230         return 0;
 231 }
 232
 233 module_init(nf_conntrack_sane_init);
 234 module_exit(nf_conntrack_sane_fini);