nf_conntrack_sane.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/* SANE connection tracking helper
  3 * (SANE = Scanner Access Now Easy)
  4 * For documentation about the SANE network protocol see
  5 * http://www.sane-project.org/html/doc015.html
  6 */
  7
  8/* Copyright (C) 2007 Red Hat, Inc.
  9 * Author: Michal Schmidt <mschmidt@redhat.com>
 10 * Based on the FTP conntrack helper (net/netfilter/nf_conntrack_ftp.c):
 11 *  (C) 1999-2001 Paul `Rusty' Russell
 12 *  (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
 13 *  (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
 14 *  (C) 2003 Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
 15 */
 16
 17#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 18
 19#include <linux/module.h>
 20#include <linux/moduleparam.h>
 21#include <linux/netfilter.h>
 22#include <linux/slab.h>
 23#include <linux/in.h>
 24#include <linux/tcp.h>
 25#include <net/netfilter/nf_conntrack.h>
 26#include <net/netfilter/nf_conntrack_helper.h>
 27#include <net/netfilter/nf_conntrack_expect.h>
 28#include <linux/netfilter/nf_conntrack_sane.h>
 29
 30#define HELPER_NAME "sane"
 31
 32MODULE_LICENSE("GPL");
 33MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
 34MODULE_DESCRIPTION("SANE connection tracking helper");
 35MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
 36
 37#define MAX_PORTS 8
 38static u_int16_t ports[MAX_PORTS];
 39static unsigned int ports_c;
 40module_param_array(ports, ushort, &ports_c, 0400);
 41
 42struct sane_request {
 43	__be32 RPC_code;
 44#define SANE_NET_START      7   /* RPC code */
 45
 46	__be32 handle;
 47};
 48
 49struct sane_reply_net_start {
 50	__be32 status;
 51#define SANE_STATUS_SUCCESS 0
 52
 53	__be16 zero;
 54	__be16 port;
 55	/* other fields aren't interesting for conntrack */
 56};
 57
 58static int help(struct sk_buff *skb,
 59		unsigned int protoff,
 60		struct nf_conn *ct,
 61		enum ip_conntrack_info ctinfo)
 62{
 63	unsigned int dataoff, datalen;
 64	const struct tcphdr *th;
 65	struct tcphdr _tcph;
 66	int ret = NF_ACCEPT;
 67	int dir = CTINFO2DIR(ctinfo);
 68	struct nf_ct_sane_master *ct_sane_info = nfct_help_data(ct);
 69	struct nf_conntrack_expect *exp;
 70	struct nf_conntrack_tuple *tuple;
 71	struct sane_reply_net_start *reply;
 72	union {
 73		struct sane_request req;
 74		struct sane_reply_net_start repl;
 75	} buf;
 76
 77	/* Until there's been traffic both ways, don't look in packets. */
 78	if (ctinfo != IP_CT_ESTABLISHED &&
 79	    ctinfo != IP_CT_ESTABLISHED_REPLY)
 80		return NF_ACCEPT;
 81
 82	/* Not a full tcp header? */
 83	th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
 84	if (th == NULL)
 85		return NF_ACCEPT;
 86
 87	/* No data? */
 88	dataoff = protoff + th->doff * 4;
 89	if (dataoff >= skb->len)
 90		return NF_ACCEPT;
 91
 92	datalen = skb->len - dataoff;
 93	if (dir == IP_CT_DIR_ORIGINAL) {
 94		const struct sane_request *req;
 95
 96		if (datalen != sizeof(struct sane_request))
 97			return NF_ACCEPT;
 98
 99		req = skb_header_pointer(skb, dataoff, datalen, &buf.req);
100		if (!req)
101			return NF_ACCEPT;
102
103		if (req->RPC_code != htonl(SANE_NET_START)) {
104			/* Not an interesting command */
105			WRITE_ONCE(ct_sane_info->state, SANE_STATE_NORMAL);
106			return NF_ACCEPT;
107		}
108
109		/* We're interested in the next reply */
110		WRITE_ONCE(ct_sane_info->state, SANE_STATE_START_REQUESTED);
111		return NF_ACCEPT;
112	}
113
114	/* IP_CT_DIR_REPLY */
115
116	/* Is it a reply to an uninteresting command? */
117	if (READ_ONCE(ct_sane_info->state) != SANE_STATE_START_REQUESTED)
118		return NF_ACCEPT;
119
120	/* It's a reply to SANE_NET_START. */
121	WRITE_ONCE(ct_sane_info->state, SANE_STATE_NORMAL);
122
123	if (datalen < sizeof(struct sane_reply_net_start)) {
124		pr_debug("NET_START reply too short\n");
125		return NF_ACCEPT;
126	}
127
128	datalen = sizeof(struct sane_reply_net_start);
129
130	reply = skb_header_pointer(skb, dataoff, datalen, &buf.repl);
131	if (!reply)
132		return NF_ACCEPT;
133
134	if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
135		/* saned refused the command */
136		pr_debug("unsuccessful SANE_STATUS = %u\n",
137			 ntohl(reply->status));
138		return NF_ACCEPT;
139	}
140
141	/* Invalid saned reply? Ignore it. */
142	if (reply->zero != 0)
143		return NF_ACCEPT;
144
145	exp = nf_ct_expect_alloc(ct);
146	if (exp == NULL) {
147		nf_ct_helper_log(skb, ct, "cannot alloc expectation");
148		return NF_DROP;
149	}
150
151	tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
152	nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
153			  &tuple->src.u3, &tuple->dst.u3,
154			  IPPROTO_TCP, NULL, &reply->port);
155
156	pr_debug("expect: ");
157	nf_ct_dump_tuple(&exp->tuple);
158
159	/* Can't expect this?  Best to drop packet now. */
160	if (nf_ct_expect_related(exp, 0) != 0) {
161		nf_ct_helper_log(skb, ct, "cannot add expectation");
162		ret = NF_DROP;
163	}
164
165	nf_ct_expect_put(exp);
166	return ret;
167}
168
169static struct nf_conntrack_helper sane[MAX_PORTS * 2] __read_mostly;
170
171static const struct nf_conntrack_expect_policy sane_exp_policy = {
172	.max_expected	= 1,
173	.timeout	= 5 * 60,
174};
175
176static void __exit nf_conntrack_sane_fini(void)
177{
178	nf_conntrack_helpers_unregister(sane, ports_c * 2);
179}
180
181static int __init nf_conntrack_sane_init(void)
182{
183	int i, ret = 0;
184
185	NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_sane_master));
186
187	if (ports_c == 0)
188		ports[ports_c++] = SANE_PORT;
189
190	/* FIXME should be configurable whether IPv4 and IPv6 connections
191		 are tracked or not - YK */
192	for (i = 0; i < ports_c; i++) {
193		nf_ct_helper_init(&sane[2 * i], AF_INET, IPPROTO_TCP,
194				  HELPER_NAME, SANE_PORT, ports[i], ports[i],
195				  &sane_exp_policy, 0, help, NULL,
196				  THIS_MODULE);
197		nf_ct_helper_init(&sane[2 * i + 1], AF_INET6, IPPROTO_TCP,
198				  HELPER_NAME, SANE_PORT, ports[i], ports[i],
199				  &sane_exp_policy, 0, help, NULL,
200				  THIS_MODULE);
201	}
202
203	ret = nf_conntrack_helpers_register(sane, ports_c * 2);
204	if (ret < 0) {
205		pr_err("failed to register helpers\n");
206		return ret;
207	}
208
209	return 0;
210}
211
212module_init(nf_conntrack_sane_init);
213module_exit(nf_conntrack_sane_fini);