/* IRC extension for IP connection tracking, Version 1.21
   * (C) 2000-2002 by Harald Welte <laforge@gnumonks.org>
   * based on RR's ip_conntrack_ftp.c

   * (C) 2006-2012 Patrick McHardy <kaber@trash.net>

   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  
  #include <linux/module.h>
  #include <linux/moduleparam.h>
  #include <linux/skbuff.h>
  #include <linux/in.h>

  #include <linux/ip.h>

  #include <linux/tcp.h>
  #include <linux/netfilter.h>

  #include <linux/slab.h>

  
  #include <net/netfilter/nf_conntrack.h>
  #include <net/netfilter/nf_conntrack_expect.h>
  #include <net/netfilter/nf_conntrack_helper.h>
  #include <linux/netfilter/nf_conntrack_irc.h>
  
  #define MAX_PORTS 8
  static unsigned short ports[MAX_PORTS];

  static unsigned int ports_c;

  static unsigned int max_dcc_channels = 8;
  static unsigned int dcc_timeout __read_mostly = 300;
  /* This is slow, but it's simple. --RR */
  static char *irc_buffer;
  static DEFINE_SPINLOCK(irc_buffer_lock);

  unsigned int (*nf_nat_irc_hook)(struct sk_buff *skb,

  				enum ip_conntrack_info ctinfo,

  				unsigned int protoff,

  				unsigned int matchoff,
  				unsigned int matchlen,
  				struct nf_conntrack_expect *exp) __read_mostly;
  EXPORT_SYMBOL_GPL(nf_nat_irc_hook);
  
  MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
  MODULE_LICENSE("GPL");
  MODULE_ALIAS("ip_conntrack_irc");

  MODULE_ALIAS_NFCT_HELPER("irc");

  
  module_param_array(ports, ushort, &ports_c, 0400);
  MODULE_PARM_DESC(ports, "port numbers of IRC servers");
  module_param(max_dcc_channels, uint, 0400);
  MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
  				   "IRC session");
  module_param(dcc_timeout, uint, 0400);
  MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");

  static const char *const dccprotos[] = {

  	"SEND ", "CHAT ", "MOVE ", "TSEND ", "SCHAT "
  };
  
  #define MINMATCHLEN	5

  /* tries to get the ip_addr and port out of a dcc command
   * return value: -1 on failure, 0 on success
   *	data		pointer to first byte of DCC command data
   *	data_end	pointer to last byte of dcc command data
   *	ip		returns parsed ip of dcc command
   *	port		returns parsed port of dcc command
   *	ad_beg_p	returns pointer to first byte of addr data
   *	ad_end_p	returns pointer to last byte of addr data
   */

  static int parse_dcc(char *data, const char *data_end, __be32 *ip,

  		     u_int16_t *port, char **ad_beg_p, char **ad_end_p)
  {

  	char *tmp;

  	/* at least 12: "AAAAAAAA P\1
  " */
  	while (*data++ != ' ')
  		if (data > data_end - 12)
  			return -1;

  	/* Make sure we have a newline character within the packet boundaries
  	 * because simple_strtoul parses until the first invalid character. */
  	for (tmp = data; tmp <= data_end; tmp++)
  		if (*tmp == '
  ')
  			break;
  	if (tmp > data_end || *tmp != '
  ')
  		return -1;

  	*ad_beg_p = data;

  	*ip = cpu_to_be32(simple_strtoul(data, &data, 10));

  
  	/* skip blanks between ip and port */
  	while (*data == ' ') {
  		if (data >= data_end)
  			return -1;
  		data++;
  	}
  
  	*port = simple_strtoul(data, &data, 10);
  	*ad_end_p = data;
  
  	return 0;
  }

  static int help(struct sk_buff *skb, unsigned int protoff,

  		struct nf_conn *ct, enum ip_conntrack_info ctinfo)
  {
  	unsigned int dataoff;

  	const struct iphdr *iph;
  	const struct tcphdr *th;
  	struct tcphdr _tcph;
  	const char *data_limit;
  	char *data, *ib_ptr;

  	int dir = CTINFO2DIR(ctinfo);
  	struct nf_conntrack_expect *exp;
  	struct nf_conntrack_tuple *tuple;

  	__be32 dcc_ip;

  	u_int16_t dcc_port;
  	__be16 port;
  	int i, ret = NF_ACCEPT;
  	char *addr_beg_p, *addr_end_p;
  	typeof(nf_nat_irc_hook) nf_nat_irc;
  
  	/* If packet is coming from IRC server */
  	if (dir == IP_CT_DIR_REPLY)
  		return NF_ACCEPT;
  
  	/* 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;
  
  	spin_lock_bh(&irc_buffer_lock);

  	ib_ptr = skb_header_pointer(skb, dataoff, skb->len - dataoff,

  				    irc_buffer);
  	BUG_ON(ib_ptr == NULL);
  
  	data = ib_ptr;

  	data_limit = ib_ptr + skb->len - dataoff;

  
  	/* strlen("\1DCC SENT t AAAAAAAA P\1
  ")=24
  	 * 5+MINMATCHLEN+strlen("t AAAAAAAA P\1
  ")=14 */
  	while (data < data_limit - (19 + MINMATCHLEN)) {
  		if (memcmp(data, "\1DCC ", 5)) {
  			data++;
  			continue;
  		}
  		data += 5;
  		/* we have at least (19+MINMATCHLEN)-5 bytes valid data left */

  		iph = ip_hdr(skb);

  		pr_debug("DCC found in master %pI4:%u %pI4:%u
  ",
  			 &iph->saddr, ntohs(th->source),
  			 &iph->daddr, ntohs(th->dest));

  
  		for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
  			if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
  				/* no match */
  				continue;
  			}
  			data += strlen(dccprotos[i]);

  			pr_debug("DCC %s detected
  ", dccprotos[i]);

  
  			/* we have at least
  			 * (19+MINMATCHLEN)-5-dccprotos[i].matchlen bytes valid
  			 * data left (== 14/13 bytes) */

  			if (parse_dcc(data, data_limit, &dcc_ip,

  				       &dcc_port, &addr_beg_p, &addr_end_p)) {

  				pr_debug("unable to parse dcc command
  ");

  				continue;
  			}

  
  			pr_debug("DCC bound ip/port: %pI4:%u
  ",
  				 &dcc_ip, dcc_port);

  
  			/* dcc_ip can be the internal OR external (NAT'ed) IP */
  			tuple = &ct->tuplehash[dir].tuple;

  			if (tuple->src.u3.ip != dcc_ip &&
  			    tuple->dst.u3.ip != dcc_ip) {

  				net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u
  ",
  						     &tuple->src.u3.ip,
  						     &dcc_ip, dcc_port);

  				continue;
  			}

  			exp = nf_ct_expect_alloc(ct);

  			if (exp == NULL) {

  				nf_ct_helper_log(skb, ct,
  						 "cannot alloc expectation");

  				ret = NF_DROP;
  				goto out;
  			}
  			tuple = &ct->tuplehash[!dir].tuple;
  			port = htons(dcc_port);

  			nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
  					  tuple->src.l3num,

  					  NULL, &tuple->dst.u3,
  					  IPPROTO_TCP, NULL, &port);

  
  			nf_nat_irc = rcu_dereference(nf_nat_irc_hook);

  			if (nf_nat_irc && ct->status & IPS_NAT_MASK)

  				ret = nf_nat_irc(skb, ctinfo, protoff,

  						 addr_beg_p - ib_ptr,
  						 addr_end_p - addr_beg_p,
  						 exp);

  			else if (nf_ct_expect_related(exp) != 0) {
  				nf_ct_helper_log(skb, ct,
  						 "cannot add expectation");

  				ret = NF_DROP;

  			}

  			nf_ct_expect_put(exp);

  			goto out;
  		}
  	}
   out:
  	spin_unlock_bh(&irc_buffer_lock);
  	return ret;
  }
  
  static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;

  static struct nf_conntrack_expect_policy irc_exp_policy;

  
  static void nf_conntrack_irc_fini(void);
  
  static int __init nf_conntrack_irc_init(void)
  {
  	int i, ret;

  
  	if (max_dcc_channels < 1) {

  		printk(KERN_ERR "nf_ct_irc: max_dcc_channels must not be zero
  ");

  		return -EINVAL;
  	}

  	irc_exp_policy.max_expected = max_dcc_channels;
  	irc_exp_policy.timeout = dcc_timeout;

  	irc_buffer = kmalloc(65536, GFP_KERNEL);
  	if (!irc_buffer)
  		return -ENOMEM;
  
  	/* If no port given, default to standard irc port */
  	if (ports_c == 0)
  		ports[ports_c++] = IRC_PORT;
  
  	for (i = 0; i < ports_c; i++) {
  		irc[i].tuple.src.l3num = AF_INET;
  		irc[i].tuple.src.u.tcp.port = htons(ports[i]);
  		irc[i].tuple.dst.protonum = IPPROTO_TCP;

  		irc[i].expect_policy = &irc_exp_policy;

  		irc[i].me = THIS_MODULE;
  		irc[i].help = help;

  		if (ports[i] == IRC_PORT)

  			sprintf(irc[i].name, "irc");

  		else

  			sprintf(irc[i].name, "irc-%u", i);

  
  		ret = nf_conntrack_helper_register(&irc[i]);
  		if (ret) {

  			printk(KERN_ERR "nf_ct_irc: failed to register helper "

  			       "for pf: %u port: %u
  ",
  			       irc[i].tuple.src.l3num, ports[i]);
  			nf_conntrack_irc_fini();
  			return ret;
  		}
  	}
  	return 0;
  }
  
  /* This function is intentionally _NOT_ defined as __exit, because
   * it is needed by the init function */
  static void nf_conntrack_irc_fini(void)
  {
  	int i;
  
  	for (i = 0; i < ports_c; i++)
  		nf_conntrack_helper_unregister(&irc[i]);
  	kfree(irc_buffer);
  }
  
  module_init(nf_conntrack_irc_init);
  module_exit(nf_conntrack_irc_fini);