/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * 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>
/* 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
             within 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 <ctype.h>
#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 alias_data *ah)
{
        if (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.
                         */
                        (void)FindUdpTcpOut(la, true_addr, destaddr,
                            true_port, 0,
                            IPPROTO_TCP, 1, &dcc_lnk);
                        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);
                        tc = (struct tcphdr *)ip_next(pip);
                        delta = GetDeltaSeqOut(tc->th_seq, lnk);
                        AddSeq(lnk, delta + copyat + iCopy - dlen, pip->ip_hl,
                            pip->ip_len, tc->th_seq, tc->th_off);
                }

                /* 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
                tcp_set_flags(tc, tcp_get_flags(tc) | TH_RES1);
#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 arbitrary
  changes in the TCP stream.  This should not be too difficult given
  this base;  I (ee) will try to do this some time later.
*/