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 = 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
162out:
163	spin_unlock_bh(&nf_sane_lock);
164	return ret;
165}
166
167static struct nf_conntrack_helper sane[MAX_PORTS][2] __read_mostly;
168
169static 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 ! */
175static 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
191static 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
236module_init(nf_conntrack_sane_init);
237module_exit(nf_conntrack_sane_fini);
238