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
32 MODULE_LICENSE("GPL");
33 MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
34 MODULE_DESCRIPTION("SANE connection tracking helper");
35 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
36
37 static char *sane_buffer;
38
39 static DEFINE_SPINLOCK(nf_sane_lock);
40
41 #define MAX_PORTS 8
42 static u_int16_t ports[MAX_PORTS];
43 static unsigned int ports_c;
44 module_param_array(ports, ushort, &ports_c, 0400);
45
46 struct sane_request {
47 __be32 RPC_code;
48 #define SANE_NET_START 7 /* RPC code */
49
50 __be32 handle;
51 };
52
53 struct sane_reply_net_start {
54 __be32 status;
55 #define SANE_STATUS_SUCCESS 0
56
57 __be16 zero;
58 __be16 port;
59 /* other fields aren't interesting for conntrack */
60 };
61
help(struct sk_buff * skb,unsigned int protoff,struct nf_conn * ct,enum ip_conntrack_info ctinfo)62 static int help(struct sk_buff *skb,
63 unsigned int protoff,
64 struct nf_conn *ct,
65 enum ip_conntrack_info ctinfo)
66 {
67 unsigned int dataoff, datalen;
68 const struct tcphdr *th;
69 struct tcphdr _tcph;
70 void *sb_ptr;
71 int ret = NF_ACCEPT;
72 int dir = CTINFO2DIR(ctinfo);
73 struct nf_ct_sane_master *ct_sane_info = nfct_help_data(ct);
74 struct nf_conntrack_expect *exp;
75 struct nf_conntrack_tuple *tuple;
76 struct sane_request *req;
77 struct sane_reply_net_start *reply;
78
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("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("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 nf_ct_helper_log(skb, ct, "cannot alloc expectation");
143 ret = NF_DROP;
144 goto out;
145 }
146
147 tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
148 nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
149 &tuple->src.u3, &tuple->dst.u3,
150 IPPROTO_TCP, NULL, &reply->port);
151
152 pr_debug("expect: ");
153 nf_ct_dump_tuple(&exp->tuple);
154
155 /* Can't expect this? Best to drop packet now. */
156 if (nf_ct_expect_related(exp, 0) != 0) {
157 nf_ct_helper_log(skb, ct, "cannot add expectation");
158 ret = NF_DROP;
159 }
160
161 nf_ct_expect_put(exp);
162
163 out:
164 spin_unlock_bh(&nf_sane_lock);
165 return ret;
166 }
167
168 static struct nf_conntrack_helper sane[MAX_PORTS * 2] __read_mostly;
169
170 static const struct nf_conntrack_expect_policy sane_exp_policy = {
171 .max_expected = 1,
172 .timeout = 5 * 60,
173 };
174
nf_conntrack_sane_fini(void)175 static void __exit nf_conntrack_sane_fini(void)
176 {
177 nf_conntrack_helpers_unregister(sane, ports_c * 2);
178 kfree(sane_buffer);
179 }
180
nf_conntrack_sane_init(void)181 static 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 sane_buffer = kmalloc(65536, GFP_KERNEL);
188 if (!sane_buffer)
189 return -ENOMEM;
190
191 if (ports_c == 0)
192 ports[ports_c++] = SANE_PORT;
193
194 /* FIXME should be configurable whether IPv4 and IPv6 connections
195 are tracked or not - YK */
196 for (i = 0; i < ports_c; i++) {
197 nf_ct_helper_init(&sane[2 * i], AF_INET, IPPROTO_TCP,
198 HELPER_NAME, SANE_PORT, ports[i], ports[i],
199 &sane_exp_policy, 0, help, NULL,
200 THIS_MODULE);
201 nf_ct_helper_init(&sane[2 * i + 1], AF_INET6, IPPROTO_TCP,
202 HELPER_NAME, SANE_PORT, ports[i], ports[i],
203 &sane_exp_policy, 0, help, NULL,
204 THIS_MODULE);
205 }
206
207 ret = nf_conntrack_helpers_register(sane, ports_c * 2);
208 if (ret < 0) {
209 pr_err("failed to register helpers\n");
210 kfree(sane_buffer);
211 return ret;
212 }
213
214 return 0;
215 }
216
217 module_init(nf_conntrack_sane_init);
218 module_exit(nf_conntrack_sane_fini);
219