/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
 31MODULE_LICENSE("GPL");
 32MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
 33MODULE_DESCRIPTION("SANE connection tracking helper");
 34MODULE_ALIAS_NFCT_HELPER("sane");
 35
 36static char *sane_buffer;
 37
 38static DEFINE_SPINLOCK(nf_sane_lock);
 39
 40#define MAX_PORTS 8
 41static u_int16_t ports[MAX_PORTS];
 42static unsigned int ports_c;
 43module_param_array(ports, ushort, &ports_c, 0400);
 44
 45struct sane_request {
 46	__be32 RPC_code;
 47#define SANE_NET_START      7   /* RPC code */
 48
 49	__be32 handle;
 50};
 51
 52struct 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
 61static 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+IP_CT_IS_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
160out:
161	spin_unlock_bh(&nf_sane_lock);
162	return ret;
163}
164
165static struct nf_conntrack_helper sane[MAX_PORTS][2] __read_mostly;
166static char sane_names[MAX_PORTS][2][sizeof("sane-65535")] __read_mostly;
167
168static const struct nf_conntrack_expect_policy sane_exp_policy = {
169	.max_expected	= 1,
170	.timeout	= 5 * 60,
171};
172
173/* don't make this __exit, since it's called from __init ! */
174static void nf_conntrack_sane_fini(void)
175{
176	int i, j;
177
178	for (i = 0; i < ports_c; i++) {
179		for (j = 0; j < 2; j++) {
180			pr_debug("nf_ct_sane: unregistering helper for pf: %d "
181				 "port: %d\n",
182				 sane[i][j].tuple.src.l3num, ports[i]);
183			nf_conntrack_helper_unregister(&sane[i][j]);
184		}
185	}
186
187	kfree(sane_buffer);
188}
189
190static int __init nf_conntrack_sane_init(void)
191{
192	int i, j = -1, ret = 0;
193	char *tmpname;
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].tuple.src.u.tcp.port = htons(ports[i]);
209			sane[i][j].tuple.dst.protonum = IPPROTO_TCP;
210			sane[i][j].expect_policy = &sane_exp_policy;
211			sane[i][j].me = THIS_MODULE;
212			sane[i][j].help = help;
213			tmpname = &sane_names[i][j][0];
214			if (ports[i] == SANE_PORT)
215				sprintf(tmpname, "sane");
216			else
217				sprintf(tmpname, "sane-%d", ports[i]);
218			sane[i][j].name = tmpname;
219
220			pr_debug("nf_ct_sane: registering helper for pf: %d "
221				 "port: %d\n",
222				 sane[i][j].tuple.src.l3num, ports[i]);
223			ret = nf_conntrack_helper_register(&sane[i][j]);
224			if (ret) {
225				printk(KERN_ERR "nf_ct_sane: failed to "
226				       "register helper for pf: %d port: %d\n",
227					sane[i][j].tuple.src.l3num, ports[i]);
228				nf_conntrack_sane_fini();
229				return ret;
230			}
231		}
232	}
233
234	return 0;
235}
236
237module_init(nf_conntrack_sane_init);
238module_exit(nf_conntrack_sane_fini);