net/netfilter/nf_conntrack_sane.c

   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);