nf_conntrack_sane.c (5606B)
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 32MODULE_LICENSE("GPL"); 33MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>"); 34MODULE_DESCRIPTION("SANE connection tracking helper"); 35MODULE_ALIAS_NFCT_HELPER(HELPER_NAME); 36 37static char *sane_buffer; 38 39static DEFINE_SPINLOCK(nf_sane_lock); 40 41#define MAX_PORTS 8 42static u_int16_t ports[MAX_PORTS]; 43static unsigned int ports_c; 44module_param_array(ports, ushort, &ports_c, 0400); 45 46struct sane_request { 47 __be32 RPC_code; 48#define SANE_NET_START 7 /* RPC code */ 49 50 __be32 handle; 51}; 52 53struct 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 62static 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 if (!sb_ptr) { 99 spin_unlock_bh(&nf_sane_lock); 100 return NF_ACCEPT; 101 } 102 103 if (dir == IP_CT_DIR_ORIGINAL) { 104 if (datalen != sizeof(struct sane_request)) 105 goto out; 106 107 req = sb_ptr; 108 if (req->RPC_code != htonl(SANE_NET_START)) { 109 /* Not an interesting command */ 110 ct_sane_info->state = SANE_STATE_NORMAL; 111 goto out; 112 } 113 114 /* We're interested in the next reply */ 115 ct_sane_info->state = SANE_STATE_START_REQUESTED; 116 goto out; 117 } 118 119 /* Is it a reply to an uninteresting command? */ 120 if (ct_sane_info->state != SANE_STATE_START_REQUESTED) 121 goto out; 122 123 /* It's a reply to SANE_NET_START. */ 124 ct_sane_info->state = SANE_STATE_NORMAL; 125 126 if (datalen < sizeof(struct sane_reply_net_start)) { 127 pr_debug("NET_START reply too short\n"); 128 goto out; 129 } 130 131 reply = sb_ptr; 132 if (reply->status != htonl(SANE_STATUS_SUCCESS)) { 133 /* saned refused the command */ 134 pr_debug("unsuccessful SANE_STATUS = %u\n", 135 ntohl(reply->status)); 136 goto out; 137 } 138 139 /* Invalid saned reply? Ignore it. */ 140 if (reply->zero != 0) 141 goto out; 142 143 exp = nf_ct_expect_alloc(ct); 144 if (exp == NULL) { 145 nf_ct_helper_log(skb, ct, "cannot alloc expectation"); 146 ret = NF_DROP; 147 goto out; 148 } 149 150 tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple; 151 nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct), 152 &tuple->src.u3, &tuple->dst.u3, 153 IPPROTO_TCP, NULL, &reply->port); 154 155 pr_debug("expect: "); 156 nf_ct_dump_tuple(&exp->tuple); 157 158 /* Can't expect this? Best to drop packet now. */ 159 if (nf_ct_expect_related(exp, 0) != 0) { 160 nf_ct_helper_log(skb, ct, "cannot add expectation"); 161 ret = NF_DROP; 162 } 163 164 nf_ct_expect_put(exp); 165 166out: 167 spin_unlock_bh(&nf_sane_lock); 168 return ret; 169} 170 171static struct nf_conntrack_helper sane[MAX_PORTS * 2] __read_mostly; 172 173static const struct nf_conntrack_expect_policy sane_exp_policy = { 174 .max_expected = 1, 175 .timeout = 5 * 60, 176}; 177 178static void __exit nf_conntrack_sane_fini(void) 179{ 180 nf_conntrack_helpers_unregister(sane, ports_c * 2); 181 kfree(sane_buffer); 182} 183 184static int __init nf_conntrack_sane_init(void) 185{ 186 int i, ret = 0; 187 188 NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_sane_master)); 189 190 sane_buffer = kmalloc(65536, GFP_KERNEL); 191 if (!sane_buffer) 192 return -ENOMEM; 193 194 if (ports_c == 0) 195 ports[ports_c++] = SANE_PORT; 196 197 /* FIXME should be configurable whether IPv4 and IPv6 connections 198 are tracked or not - YK */ 199 for (i = 0; i < ports_c; i++) { 200 nf_ct_helper_init(&sane[2 * i], AF_INET, IPPROTO_TCP, 201 HELPER_NAME, SANE_PORT, ports[i], ports[i], 202 &sane_exp_policy, 0, help, NULL, 203 THIS_MODULE); 204 nf_ct_helper_init(&sane[2 * i + 1], AF_INET6, IPPROTO_TCP, 205 HELPER_NAME, SANE_PORT, ports[i], ports[i], 206 &sane_exp_policy, 0, help, NULL, 207 THIS_MODULE); 208 } 209 210 ret = nf_conntrack_helpers_register(sane, ports_c * 2); 211 if (ret < 0) { 212 pr_err("failed to register helpers\n"); 213 kfree(sane_buffer); 214 return ret; 215 } 216 217 return 0; 218} 219 220module_init(nf_conntrack_sane_init); 221module_exit(nf_conntrack_sane_fini);