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// SPDX-License-Identifier: GPL-2.0-only
/* SANE connection tracking helper
* (SANE = Scanner Access Now Easy)
* For documentation about the SANE network protocol see
* http://www.sane-project.org/html/doc015.html
*/
/* Copyright (C) 2007 Red Hat, Inc.
* Author: Michal Schmidt <mschmidt@redhat.com>
* Based on the FTP conntrack helper (net/netfilter/nf_conntrack_ftp.c):
* (C) 1999-2001 Paul `Rusty' Russell
* (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
* (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
* (C) 2003 Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/netfilter.h>
#include <linux/slab.h>
#include <linux/in.h>
#include <linux/tcp.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <linux/netfilter/nf_conntrack_sane.h>
#define HELPER_NAME "sane"
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Michal Schmidt <mschmidt@redhat.com>");
MODULE_DESCRIPTION("SANE connection tracking helper");
MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
#define MAX_PORTS 8
static u_int16_t ports[MAX_PORTS];
static unsigned int ports_c;
module_param_array(ports, ushort, &ports_c, 0400);
struct sane_request {
__be32 RPC_code;
#define SANE_NET_START 7 /* RPC code */
__be32 handle;
};
struct sane_reply_net_start {
__be32 status;
#define SANE_STATUS_SUCCESS 0
__be16 zero;
__be16 port;
/* other fields aren't interesting for conntrack */
};
static int help(struct sk_buff *skb,
unsigned int protoff,
struct nf_conn *ct,
enum ip_conntrack_info ctinfo)
{
unsigned int dataoff, datalen;
const struct tcphdr *th;
struct tcphdr _tcph;
int ret = NF_ACCEPT;
int dir = CTINFO2DIR(ctinfo);
struct nf_ct_sane_master *ct_sane_info = nfct_help_data(ct);
struct nf_conntrack_expect *exp;
struct nf_conntrack_tuple *tuple;
struct sane_reply_net_start *reply;
union {
struct sane_request req;
struct sane_reply_net_start repl;
} buf;
/* Until there's been traffic both ways, don't look in packets. */
if (ctinfo != IP_CT_ESTABLISHED &&
ctinfo != IP_CT_ESTABLISHED_REPLY)
return NF_ACCEPT;
/* Not a full tcp header? */
th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
if (th == NULL)
return NF_ACCEPT;
/* No data? */
dataoff = protoff + th->doff * 4;
if (dataoff >= skb->len)
return NF_ACCEPT;
datalen = skb->len - dataoff;
if (dir == IP_CT_DIR_ORIGINAL) {
const struct sane_request *req;
if (datalen != sizeof(struct sane_request))
return NF_ACCEPT;
req = skb_header_pointer(skb, dataoff, datalen, &buf.req);
if (!req)
return NF_ACCEPT;
if (req->RPC_code != htonl(SANE_NET_START)) {
/* Not an interesting command */
WRITE_ONCE(ct_sane_info->state, SANE_STATE_NORMAL);
return NF_ACCEPT;
}
/* We're interested in the next reply */
WRITE_ONCE(ct_sane_info->state, SANE_STATE_START_REQUESTED);
return NF_ACCEPT;
}
/* IP_CT_DIR_REPLY */
/* Is it a reply to an uninteresting command? */
if (READ_ONCE(ct_sane_info->state) != SANE_STATE_START_REQUESTED)
return NF_ACCEPT;
/* It's a reply to SANE_NET_START. */
WRITE_ONCE(ct_sane_info->state, SANE_STATE_NORMAL);
if (datalen < sizeof(struct sane_reply_net_start)) {
pr_debug("NET_START reply too short\n");
return NF_ACCEPT;
}
datalen = sizeof(struct sane_reply_net_start);
reply = skb_header_pointer(skb, dataoff, datalen, &buf.repl);
if (!reply)
return NF_ACCEPT;
if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
/* saned refused the command */
pr_debug("unsuccessful SANE_STATUS = %u\n",
ntohl(reply->status));
return NF_ACCEPT;
}
/* Invalid saned reply? Ignore it. */
if (reply->zero != 0)
return NF_ACCEPT;
exp = nf_ct_expect_alloc(ct);
if (exp == NULL) {
nf_ct_helper_log(skb, ct, "cannot alloc expectation");
return NF_DROP;
}
tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
&tuple->src.u3, &tuple->dst.u3,
IPPROTO_TCP, NULL, &reply->port);
pr_debug("expect: ");
nf_ct_dump_tuple(&exp->tuple);
/* Can't expect this? Best to drop packet now. */
if (nf_ct_expect_related(exp, 0) != 0) {
nf_ct_helper_log(skb, ct, "cannot add expectation");
ret = NF_DROP;
}
nf_ct_expect_put(exp);
return ret;
}
static struct nf_conntrack_helper sane[MAX_PORTS * 2] __read_mostly;
static const struct nf_conntrack_expect_policy sane_exp_policy = {
.max_expected = 1,
.timeout = 5 * 60,
};
static void __exit nf_conntrack_sane_fini(void)
{
nf_conntrack_helpers_unregister(sane, ports_c * 2);
}
static int __init nf_conntrack_sane_init(void)
{
int i, ret = 0;
NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_sane_master));
if (ports_c == 0)
ports[ports_c++] = SANE_PORT;
/* FIXME should be configurable whether IPv4 and IPv6 connections
are tracked or not - YK */
for (i = 0; i < ports_c; i++) {
nf_ct_helper_init(&sane[2 * i], AF_INET, IPPROTO_TCP,
HELPER_NAME, SANE_PORT, ports[i], ports[i],
&sane_exp_policy, 0, help, NULL,
THIS_MODULE);
nf_ct_helper_init(&sane[2 * i + 1], AF_INET6, IPPROTO_TCP,
HELPER_NAME, SANE_PORT, ports[i], ports[i],
&sane_exp_policy, 0, help, NULL,
THIS_MODULE);
}
ret = nf_conntrack_helpers_register(sane, ports_c * 2);
if (ret < 0) {
pr_err("failed to register helpers\n");
return ret;
}
return 0;
}
module_init(nf_conntrack_sane_init);
module_exit(nf_conntrack_sane_fini);
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