/* 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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#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\n" */
        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 == '\n')
                        break;
        if (tmp > data_end || *tmp != '\n')
                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\n")=24
         * 5+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=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\n",
                         &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\n", 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\n");
                                continue;
                        }

                        pr_debug("DCC bound ip/port: %pI4:%u\n",
                                 &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\n",
                                                     &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) {
                pr_err("max_dcc_channels must not be zero\n");
                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) {
                        pr_err("failed to register helper for pf: %u port: %u\n",
                               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);