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                 ret = NF_DROP;
 142                 goto out;
 143         }
 144
 145         tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 146         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
 147                           &tuple->src.u3, &tuple->dst.u3,
 148                           IPPROTO_TCP, NULL, &reply->port);
 149
 150         pr_debug("nf_ct_sane: expect: ");
 151         nf_ct_dump_tuple(&exp->tuple);
 152
 153         /* Can't expect this?  Best to drop packet now. */
 154         if (nf_ct_expect_related(exp) != 0)
 155                 ret = NF_DROP;
 156
 157         nf_ct_expect_put(exp);
 158
 159 out:
 160         spin_unlock_bh(&nf_sane_lock);
 161         return ret;
 162 }
 163
 164 static struct nf_conntrack_helper sane[MAX_PORTS][2] __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
 192         sane_buffer = kmalloc(65536, GFP_KERNEL);
 193         if (!sane_buffer)
 194                 return -ENOMEM;
 195
 196         if (ports_c == 0)
 197                 ports[ports_c++] = SANE_PORT;
 198
 199         /* FIXME should be configurable whether IPv4 and IPv6 connections
 200                  are tracked or not - YK */
 201         for (i = 0; i < ports_c; i++) {
 202                 sane[i][0].tuple.src.l3num = PF_INET;
 203                 sane[i][1].tuple.src.l3num = PF_INET6;
 204                 for (j = 0; j < 2; j++) {
 205                         sane[i][j].data_len = sizeof(struct nf_ct_sane_master);
 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);