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Linux/net/netfilter/nf_conntrack_sane.c

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  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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 21 
 22 #include <linux/module.h>
 23 #include <linux/moduleparam.h>
 24 #include <linux/netfilter.h>
 25 #include <linux/slab.h>
 26 #include <linux/in.h>
 27 #include <linux/tcp.h>
 28 #include <net/netfilter/nf_conntrack.h>
 29 #include <net/netfilter/nf_conntrack_helper.h>
 30 #include <net/netfilter/nf_conntrack_expect.h>
 31 #include <linux/netfilter/nf_conntrack_sane.h>
 32 
 33 MODULE_LICENSE("GPL");
 34 MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
 35 MODULE_DESCRIPTION("SANE connection tracking helper");
 36 MODULE_ALIAS_NFCT_HELPER("sane");
 37 
 38 static char *sane_buffer;
 39 
 40 static DEFINE_SPINLOCK(nf_sane_lock);
 41 
 42 #define MAX_PORTS 8
 43 static u_int16_t ports[MAX_PORTS];
 44 static unsigned int ports_c;
 45 module_param_array(ports, ushort, &ports_c, 0400);
 46 
 47 struct sane_request {
 48         __be32 RPC_code;
 49 #define SANE_NET_START      7   /* RPC code */
 50 
 51         __be32 handle;
 52 };
 53 
 54 struct sane_reply_net_start {
 55         __be32 status;
 56 #define SANE_STATUS_SUCCESS 0
 57 
 58         __be16 zero;
 59         __be16 port;
 60         /* other fields aren't interesting for conntrack */
 61 };
 62 
 63 static int help(struct sk_buff *skb,
 64                 unsigned int protoff,
 65                 struct nf_conn *ct,
 66                 enum ip_conntrack_info ctinfo)
 67 {
 68         unsigned int dataoff, datalen;
 69         const struct tcphdr *th;
 70         struct tcphdr _tcph;
 71         void *sb_ptr;
 72         int ret = NF_ACCEPT;
 73         int dir = CTINFO2DIR(ctinfo);
 74         struct nf_ct_sane_master *ct_sane_info = nfct_help_data(ct);
 75         struct nf_conntrack_expect *exp;
 76         struct nf_conntrack_tuple *tuple;
 77         struct sane_request *req;
 78         struct sane_reply_net_start *reply;
 79 
 80         /* Until there's been traffic both ways, don't look in packets. */
 81         if (ctinfo != IP_CT_ESTABLISHED &&
 82             ctinfo != IP_CT_ESTABLISHED_REPLY)
 83                 return NF_ACCEPT;
 84 
 85         /* Not a full tcp header? */
 86         th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
 87         if (th == NULL)
 88                 return NF_ACCEPT;
 89 
 90         /* No data? */
 91         dataoff = protoff + th->doff * 4;
 92         if (dataoff >= skb->len)
 93                 return NF_ACCEPT;
 94 
 95         datalen = skb->len - dataoff;
 96 
 97         spin_lock_bh(&nf_sane_lock);
 98         sb_ptr = skb_header_pointer(skb, dataoff, datalen, sane_buffer);
 99         BUG_ON(sb_ptr == NULL);
100 
101         if (dir == IP_CT_DIR_ORIGINAL) {
102                 if (datalen != sizeof(struct sane_request))
103                         goto out;
104 
105                 req = sb_ptr;
106                 if (req->RPC_code != htonl(SANE_NET_START)) {
107                         /* Not an interesting command */
108                         ct_sane_info->state = SANE_STATE_NORMAL;
109                         goto out;
110                 }
111 
112                 /* We're interested in the next reply */
113                 ct_sane_info->state = SANE_STATE_START_REQUESTED;
114                 goto out;
115         }
116 
117         /* Is it a reply to an uninteresting command? */
118         if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
119                 goto out;
120 
121         /* It's a reply to SANE_NET_START. */
122         ct_sane_info->state = SANE_STATE_NORMAL;
123 
124         if (datalen < sizeof(struct sane_reply_net_start)) {
125                 pr_debug("NET_START reply too short\n");
126                 goto out;
127         }
128 
129         reply = sb_ptr;
130         if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
131                 /* saned refused the command */
132                 pr_debug("unsuccessful SANE_STATUS = %u\n",
133                          ntohl(reply->status));
134                 goto out;
135         }
136 
137         /* Invalid saned reply? Ignore it. */
138         if (reply->zero != 0)
139                 goto out;
140 
141         exp = nf_ct_expect_alloc(ct);
142         if (exp == NULL) {
143                 nf_ct_helper_log(skb, ct, "cannot alloc expectation");
144                 ret = NF_DROP;
145                 goto out;
146         }
147 
148         tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
149         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
150                           &tuple->src.u3, &tuple->dst.u3,
151                           IPPROTO_TCP, NULL, &reply->port);
152 
153         pr_debug("expect: ");
154         nf_ct_dump_tuple(&exp->tuple);
155 
156         /* Can't expect this?  Best to drop packet now. */
157         if (nf_ct_expect_related(exp) != 0) {
158                 nf_ct_helper_log(skb, ct, "cannot add expectation");
159                 ret = NF_DROP;
160         }
161 
162         nf_ct_expect_put(exp);
163 
164 out:
165         spin_unlock_bh(&nf_sane_lock);
166         return ret;
167 }
168 
169 static struct nf_conntrack_helper sane[MAX_PORTS * 2] __read_mostly;
170 
171 static const struct nf_conntrack_expect_policy sane_exp_policy = {
172         .max_expected   = 1,
173         .timeout        = 5 * 60,
174 };
175 
176 static void __exit nf_conntrack_sane_fini(void)
177 {
178         nf_conntrack_helpers_unregister(sane, ports_c * 2);
179         kfree(sane_buffer);
180 }
181 
182 static int __init nf_conntrack_sane_init(void)
183 {
184         int i, ret = 0;
185 
186         NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_sane_master));
187 
188         sane_buffer = kmalloc(65536, GFP_KERNEL);
189         if (!sane_buffer)
190                 return -ENOMEM;
191 
192         if (ports_c == 0)
193                 ports[ports_c++] = SANE_PORT;
194 
195         /* FIXME should be configurable whether IPv4 and IPv6 connections
196                  are tracked or not - YK */
197         for (i = 0; i < ports_c; i++) {
198                 nf_ct_helper_init(&sane[2 * i], AF_INET, IPPROTO_TCP, "sane",
199                                   SANE_PORT, ports[i], ports[i],
200                                   &sane_exp_policy, 0, help, NULL,
201                                   THIS_MODULE);
202                 nf_ct_helper_init(&sane[2 * i + 1], AF_INET6, IPPROTO_TCP, "sane",
203                                   SANE_PORT, ports[i], ports[i],
204                                   &sane_exp_policy, 0, help, NULL,
205                                   THIS_MODULE);
206         }
207 
208         ret = nf_conntrack_helpers_register(sane, ports_c * 2);
209         if (ret < 0) {
210                 pr_err("failed to register helpers\n");
211                 kfree(sane_buffer);
212                 return ret;
213         }
214 
215         return 0;
216 }
217 
218 module_init(nf_conntrack_sane_init);
219 module_exit(nf_conntrack_sane_fini);
220 

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