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