/*-
 * Copyright (c) 2001 Charles Mott <cm@linktel.net>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: src/sys/netinet/libalias/alias_irc.c,v 1.23.2.2.4.1 2009/04/15 03:14:26 kensmith Exp $");

/* Alias_irc.c intercepts packages contain IRC CTCP commands, and
    changes DCC commands to export a port on the aliasing host instead
    of an aliased host.

    For this routine to work, the DCC command must fit entirely into a
    single TCP packet.  This will usually happen, but is not
    guaranteed.

     The interception is likely to change the length of the packet.
     The handling of this is copied more-or-less verbatim from
     ftp_alias.c

     Initial version: Eivind Eklund <perhaps@yes.no> (ee) 97-01-29

     Version 2.1:  May, 1997 (cjm)
         Very minor changes to conform with
         local/global/function naming conventions
         withing the packet alising module.
*/

/* Includes */
#ifdef _KERNEL
#include <sys/param.h>
#include <sys/ctype.h>
#include <sys/limits.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/module.h>
#else
#include <errno.h>
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#endif

#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>

#ifdef _KERNEL
#include <netinet/libalias/alias.h>
#include <netinet/libalias/alias_local.h>
#include <netinet/libalias/alias_mod.h>
#else
#include "alias_local.h"
#include "alias_mod.h"
#endif

#define IRC_CONTROL_PORT_NUMBER_1 6667
#define IRC_CONTROL_PORT_NUMBER_2 6668

#define PKTSIZE (IP_MAXPACKET + 1)
char *newpacket;

/* Local defines */
#define DBprintf(a)

static void
AliasHandleIrcOut(struct libalias *, struct ip *, struct alias_link *,
          int maxpacketsize);

static int
fingerprint(struct libalias *la, struct ip *pip, struct alias_data *ah)
{

    if (ah->dport == NULL || ah->dport == NULL || ah->lnk == NULL ||
        ah->maxpktsize == 0)
        return (-1);
    if (ntohs(*ah->dport) == IRC_CONTROL_PORT_NUMBER_1
        || ntohs(*ah->dport) == IRC_CONTROL_PORT_NUMBER_2)
        return (0);
    return (-1);
}

static int
protohandler(struct libalias *la, struct ip *pip, struct alias_data *ah)
{

    newpacket = malloc(PKTSIZE);
    if (newpacket) {
        AliasHandleIrcOut(la, pip, ah->lnk, ah->maxpktsize);
        free(newpacket);
    }
    return (0);
}

struct proto_handler handlers[] = {
    {
      .pri = 90,
      .dir = OUT,
      .proto = TCP,
      .fingerprint = &fingerprint,
      .protohandler = &protohandler
    },
    { EOH }
};

static int
mod_handler(module_t mod, int type, void *data)
{
    int error;

    switch (type) {
    case MOD_LOAD:
        error = 0;
        LibAliasAttachHandlers(handlers);
        break;
    case MOD_UNLOAD:
        error = 0;
        LibAliasDetachHandlers(handlers);
        break;
    default:
        error = EINVAL;
    }
    return (error);
}

#ifdef _KERNEL
static
#endif
moduledata_t alias_mod = {
       "alias_irc", mod_handler, NULL
};

/* Kernel module definition. */
#ifdef  _KERNEL
DECLARE_MODULE(alias_irc, alias_mod, SI_SUB_DRIVERS, SI_ORDER_SECOND);
MODULE_VERSION(alias_irc, 1);
MODULE_DEPEND(alias_irc, libalias, 1, 1, 1);
#endif

static void
AliasHandleIrcOut(struct libalias *la,
    struct ip *pip,     /* IP packet to examine */
    struct alias_link *lnk, /* Which link are we on? */
    int maxsize         /* Maximum size of IP packet including
                 * headers */
)
{
    int hlen, tlen, dlen;
    struct in_addr true_addr;
    u_short true_port;
    char *sptr;
    struct tcphdr *tc;
    int i;          /* Iterator through the source */

/* Calculate data length of TCP packet */
    tc = (struct tcphdr *)ip_next(pip);
    hlen = (pip->ip_hl + tc->th_off) << 2;
    tlen = ntohs(pip->ip_len);
    dlen = tlen - hlen;

    /*
     * Return if data length is too short - assume an entire PRIVMSG in
     * each packet.
     */
    if (dlen < (int)sizeof(":A!a@n.n PRIVMSG A :aDCC 1 1a") - 1)
        return;

/* Place string pointer at beginning of data */
    sptr = (char *)pip;
    sptr += hlen;
    maxsize -= hlen;    /* We're interested in maximum size of
                 * data, not packet */

    /* Search for a CTCP command [Note 1] */
    for (i = 0; i < dlen; i++) {
        if (sptr[i] == '\001')
            goto lFOUND_CTCP;
    }
    return;         /* No CTCP commands in  */
    /* Handle CTCP commands - the buffer may have to be copied */
lFOUND_CTCP:
    {
        unsigned int copyat = i;
        unsigned int iCopy = 0; /* How much data have we written to
                     * copy-back string? */
        unsigned long org_addr; /* Original IP address */
        unsigned short org_port;    /* Original source port
                         * address */

lCTCP_START:
        if (i >= dlen || iCopy >= PKTSIZE)
            goto lPACKET_DONE;
        newpacket[iCopy++] = sptr[i++]; /* Copy the CTCP start
                         * character */
        /* Start of a CTCP */
        if (i + 4 >= dlen)  /* Too short for DCC */
            goto lBAD_CTCP;
        if (sptr[i + 0] != 'D')
            goto lBAD_CTCP;
        if (sptr[i + 1] != 'C')
            goto lBAD_CTCP;
        if (sptr[i + 2] != 'C')
            goto lBAD_CTCP;
        if (sptr[i + 3] != ' ')
            goto lBAD_CTCP;
        /* We have a DCC command - handle it! */
        i += 4;     /* Skip "DCC " */
        if (iCopy + 4 > PKTSIZE)
            goto lPACKET_DONE;
        newpacket[iCopy++] = 'D';
        newpacket[iCopy++] = 'C';
        newpacket[iCopy++] = 'C';
        newpacket[iCopy++] = ' ';

        DBprintf(("Found DCC\n"));
        /*
         * Skip any extra spaces (should not occur according to
         * protocol, but DCC breaks CTCP protocol anyway
         */
        while (sptr[i] == ' ') {
            if (++i >= dlen) {
                DBprintf(("DCC packet terminated in just spaces\n"));
                goto lPACKET_DONE;
            }
        }

        DBprintf(("Transferring command...\n"));
        while (sptr[i] != ' ') {
            newpacket[iCopy++] = sptr[i];
            if (++i >= dlen || iCopy >= PKTSIZE) {
                DBprintf(("DCC packet terminated during command\n"));
                goto lPACKET_DONE;
            }
        }
        /* Copy _one_ space */
        if (i + 1 < dlen && iCopy < PKTSIZE)
            newpacket[iCopy++] = sptr[i++];

        DBprintf(("Done command - removing spaces\n"));
        /*
         * Skip any extra spaces (should not occur according to
         * protocol, but DCC breaks CTCP protocol anyway
         */
        while (sptr[i] == ' ') {
            if (++i >= dlen) {
                DBprintf(("DCC packet terminated in just spaces (post-command)\n"));
                goto lPACKET_DONE;
            }
        }

        DBprintf(("Transferring filename...\n"));
        while (sptr[i] != ' ') {
            newpacket[iCopy++] = sptr[i];
            if (++i >= dlen || iCopy >= PKTSIZE) {
                DBprintf(("DCC packet terminated during filename\n"));
                goto lPACKET_DONE;
            }
        }
        /* Copy _one_ space */
        if (i + 1 < dlen && iCopy < PKTSIZE)
            newpacket[iCopy++] = sptr[i++];

        DBprintf(("Done filename - removing spaces\n"));
        /*
         * Skip any extra spaces (should not occur according to
         * protocol, but DCC breaks CTCP protocol anyway
         */
        while (sptr[i] == ' ') {
            if (++i >= dlen) {
                DBprintf(("DCC packet terminated in just spaces (post-filename)\n"));
                goto lPACKET_DONE;
            }
        }

        DBprintf(("Fetching IP address\n"));
        /* Fetch IP address */
        org_addr = 0;
        while (i < dlen && isdigit(sptr[i])) {
            if (org_addr > ULONG_MAX / 10UL) {  /* Terminate on overflow */
                DBprintf(("DCC Address overflow (org_addr == 0x%08lx, next char %c\n", org_addr, sptr[i]));
                goto lBAD_CTCP;
            }
            org_addr *= 10;
            org_addr += sptr[i++] - '0';
        }
        DBprintf(("Skipping space\n"));
        if (i + 1 >= dlen || sptr[i] != ' ') {
            DBprintf(("Overflow (%d >= %d) or bad character (%02x) terminating IP address\n", i + 1, dlen, sptr[i]));
            goto lBAD_CTCP;
        }
        /*
         * Skip any extra spaces (should not occur according to
         * protocol, but DCC breaks CTCP protocol anyway, so we
         * might as well play it safe
         */
        while (sptr[i] == ' ') {
            if (++i >= dlen) {
                DBprintf(("Packet failure - space overflow.\n"));
                goto lPACKET_DONE;
            }
        }
        DBprintf(("Fetching port number\n"));
        /* Fetch source port */
        org_port = 0;
        while (i < dlen && isdigit(sptr[i])) {
            if (org_port > 6554) {  /* Terminate on overflow
                         * (65536/10 rounded up */
                DBprintf(("DCC: port number overflow\n"));
                goto lBAD_CTCP;
            }
            org_port *= 10;
            org_port += sptr[i++] - '0';
        }
        /* Skip illegal addresses (or early termination) */
        if (i >= dlen || (sptr[i] != '\001' && sptr[i] != ' ')) {
            DBprintf(("Bad port termination\n"));
            goto lBAD_CTCP;
        }
        DBprintf(("Got IP %lu and port %u\n", org_addr, (unsigned)org_port));

        /* We've got the address and port - now alias it */
        {
            struct alias_link *dcc_lnk;
            struct in_addr destaddr;


            true_port = htons(org_port);
            true_addr.s_addr = htonl(org_addr);
            destaddr.s_addr = 0;

            /* Sanity/Security checking */
            if (!org_addr || !org_port ||
                pip->ip_src.s_addr != true_addr.s_addr ||
                org_port < IPPORT_RESERVED)
                goto lBAD_CTCP;

            /*
             * Steal the FTP_DATA_PORT - it doesn't really
             * matter, and this would probably allow it through
             * at least _some_ firewalls.
             */
            dcc_lnk = FindUdpTcpOut(la, true_addr, destaddr,
                true_port, 0,
                IPPROTO_TCP, 1);
            DBprintf(("Got a DCC link\n"));
            if (dcc_lnk) {
                struct in_addr alias_address;   /* Address from aliasing */
                u_short alias_port; /* Port given by
                             * aliasing */
                int n;

#ifndef NO_FW_PUNCH
                /* Generate firewall hole as appropriate */
                PunchFWHole(dcc_lnk);
#endif

                alias_address = GetAliasAddress(lnk);
                n = snprintf(&newpacket[iCopy],
                    PKTSIZE - iCopy,
                    "%lu ", (u_long) htonl(alias_address.s_addr));
                if (n < 0) {
                    DBprintf(("DCC packet construct failure.\n"));
                    goto lBAD_CTCP;
                }
                if ((iCopy += n) >= PKTSIZE) {  /* Truncated/fit exactly
                                         * - bad news */
                    DBprintf(("DCC constructed packet overflow.\n"));
                    goto lBAD_CTCP;
                }
                alias_port = GetAliasPort(dcc_lnk);
                n = snprintf(&newpacket[iCopy],
                    PKTSIZE - iCopy,
                    "%u", htons(alias_port));
                if (n < 0) {
                    DBprintf(("DCC packet construct failure.\n"));
                    goto lBAD_CTCP;
                }
                iCopy += n;
                /*
                 * Done - truncated cases will be taken
                 * care of by lBAD_CTCP
                 */
                DBprintf(("Aliased IP %lu and port %u\n", alias_address.s_addr, (unsigned)alias_port));
            }
        }
        /*
         * An uninteresting CTCP - state entered right after '\001'
         * has been pushed.  Also used to copy the rest of a DCC,
         * after IP address and port has been handled
         */
lBAD_CTCP:
        for (; i < dlen && iCopy < PKTSIZE; i++, iCopy++) {
            newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */
            if (sptr[i] == '\001') {
                goto lNORMAL_TEXT;
            }
        }
        goto lPACKET_DONE;
        /* Normal text */
lNORMAL_TEXT:
        for (; i < dlen && iCopy < PKTSIZE; i++, iCopy++) {
            newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */
            if (sptr[i] == '\001') {
                goto lCTCP_START;
            }
        }
        /* Handle the end of a packet */
lPACKET_DONE:
        iCopy = iCopy > maxsize - copyat ? maxsize - copyat : iCopy;
        memcpy(sptr + copyat, newpacket, iCopy);

/* Save information regarding modified seq and ack numbers */
        {
            int delta;

            SetAckModified(lnk);
            delta = GetDeltaSeqOut(pip, lnk);
            AddSeq(pip, lnk, delta + copyat + iCopy - dlen);
        }

        /* Revise IP header */
        {
            u_short new_len;

            new_len = htons(hlen + iCopy + copyat);
            DifferentialChecksum(&pip->ip_sum,
                &new_len,
                &pip->ip_len,
                1);
            pip->ip_len = new_len;
        }

        /* Compute TCP checksum for revised packet */
        tc->th_sum = 0;
#ifdef _KERNEL
        tc->th_x2 = 1;
#else
        tc->th_sum = TcpChecksum(pip);
#endif
        return;
    }
}

/* Notes:
    [Note 1]
    The initial search will most often fail; it could be replaced with a 32-bit specific search.
    Such a search would be done for 32-bit unsigned value V:
    V ^= 0x01010101;                  (Search is for null bytes)
    if( ((V-0x01010101)^V) & 0x80808080 ) {
     (found a null bytes which was a 01 byte)
    }
   To assert that the processor is 32-bits, do
   extern int ircdccar[32];        (32 bits)
   extern int ircdccar[CHAR_BIT*sizeof(unsigned int)];
   which will generate a type-error on all but 32-bit machines.

    [Note 2] This routine really ought to be replaced with one that
    creates a transparent proxy on the aliasing host, to allow arbitary
    changes in the TCP stream.  This should not be too difficult given
    this base;  I (ee) will try to do this some time later.
    */
