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 #define MAX_PORTS 8 38 static u_int16_t ports[MAX_PORTS]; 39 static unsigned int ports_c; 40 module_param_array(ports, ushort, &ports_c, 0400); 41 42 struct sane_request { 43 __be32 RPC_code; 44 #define SANE_NET_START 7 /* RPC code */ 45 46 __be32 handle; 47 }; 48 49 struct 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 58 static 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 } 168 169 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 } 180 181 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 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 } 211 212 module_init(nf_conntrack_sane_init); 213 module_exit(nf_conntrack_sane_fini); 214