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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 #include <linux/module.h>
 21 #include <linux/moduleparam.h>
 22 #include <linux/netfilter.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 MODULE_LICENSE("GPL");
 31 MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
 32 MODULE_DESCRIPTION("SANE connection tracking helper");
 33 MODULE_ALIAS_NFCT_HELPER("sane");
 34 
 35 static char *sane_buffer;
 36 
 37 static DEFINE_SPINLOCK(nf_sane_lock);
 38 
 39 #define MAX_PORTS 8
 40 static u_int16_t ports[MAX_PORTS];
 41 static unsigned int ports_c;
 42 module_param_array(ports, ushort, &ports_c, 0400);
 43 
 44 struct sane_request {
 45         __be32 RPC_code;
 46 #define SANE_NET_START      7   /* RPC code */
 47 
 48         __be32 handle;
 49 };
 50 
 51 struct sane_reply_net_start {
 52         __be32 status;
 53 #define SANE_STATUS_SUCCESS 0
 54 
 55         __be16 zero;
 56         __be16 port;
 57         /* other fields aren't interesting for conntrack */
 58 };
 59 
 60 static int help(struct sk_buff *skb,
 61                 unsigned int protoff,
 62                 struct nf_conn *ct,
 63                 enum ip_conntrack_info ctinfo)
 64 {
 65         unsigned int dataoff, datalen;
 66         const struct tcphdr *th;
 67         struct tcphdr _tcph;
 68         void *sb_ptr;
 69         int ret = NF_ACCEPT;
 70         int dir = CTINFO2DIR(ctinfo);
 71         struct nf_ct_sane_master *ct_sane_info;
 72         struct nf_conntrack_expect *exp;
 73         struct nf_conntrack_tuple *tuple;
 74         struct sane_request *req;
 75         struct sane_reply_net_start *reply;
 76 
 77         ct_sane_info = &nfct_help(ct)->help.ct_sane_info;
 78         /* Until there's been traffic both ways, don't look in packets. */
 79         if (ctinfo != IP_CT_ESTABLISHED &&
 80             ctinfo != IP_CT_ESTABLISHED+IP_CT_IS_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                 ret = NF_DROP;
142                 goto out;
143         }
144 
145         tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
146         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
147                           &tuple->src.u3, &tuple->dst.u3,
148                           IPPROTO_TCP, NULL, &reply->port);
149 
150         pr_debug("nf_ct_sane: expect: ");
151         nf_ct_dump_tuple(&exp->tuple);
152 
153         /* Can't expect this?  Best to drop packet now. */
154         if (nf_ct_expect_related(exp) != 0)
155                 ret = NF_DROP;
156 
157         nf_ct_expect_put(exp);
158 
159 out:
160         spin_unlock_bh(&nf_sane_lock);
161         return ret;
162 }
163 
164 static struct nf_conntrack_helper sane[MAX_PORTS][2] __read_mostly;
165 static char sane_names[MAX_PORTS][2][sizeof("sane-65535")] __read_mostly;
166 
167 static const struct nf_conntrack_expect_policy sane_exp_policy = {
168         .max_expected   = 1,
169         .timeout        = 5 * 60,
170 };
171 
172 /* don't make this __exit, since it's called from __init ! */
173 static void nf_conntrack_sane_fini(void)
174 {
175         int i, j;
176 
177         for (i = 0; i < ports_c; i++) {
178                 for (j = 0; j < 2; j++) {
179                         pr_debug("nf_ct_sane: unregistering helper for pf: %d "
180                                  "port: %d\n",
181                                  sane[i][j].tuple.src.l3num, ports[i]);
182                         nf_conntrack_helper_unregister(&sane[i][j]);
183                 }
184         }
185 
186         kfree(sane_buffer);
187 }
188 
189 static int __init nf_conntrack_sane_init(void)
190 {
191         int i, j = -1, ret = 0;
192         char *tmpname;
193 
194         sane_buffer = kmalloc(65536, GFP_KERNEL);
195         if (!sane_buffer)
196                 return -ENOMEM;
197 
198         if (ports_c == 0)
199                 ports[ports_c++] = SANE_PORT;
200 
201         /* FIXME should be configurable whether IPv4 and IPv6 connections
202                  are tracked or not - YK */
203         for (i = 0; i < ports_c; i++) {
204                 sane[i][0].tuple.src.l3num = PF_INET;
205                 sane[i][1].tuple.src.l3num = PF_INET6;
206                 for (j = 0; j < 2; j++) {
207                         sane[i][j].tuple.src.u.tcp.port = htons(ports[i]);
208                         sane[i][j].tuple.dst.protonum = IPPROTO_TCP;
209                         sane[i][j].expect_policy = &sane_exp_policy;
210                         sane[i][j].me = THIS_MODULE;
211                         sane[i][j].help = help;
212                         tmpname = &sane_names[i][j][0];
213                         if (ports[i] == SANE_PORT)
214                                 sprintf(tmpname, "sane");
215                         else
216                                 sprintf(tmpname, "sane-%d", ports[i]);
217                         sane[i][j].name = tmpname;
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 
236 module_init(nf_conntrack_sane_init);
237 module_exit(nf_conntrack_sane_fini);
238 

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