/*
 *  Copyright (C) 2013-2020 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
 *  Copyright (C) 2007-2013 Sourcefire, Inc.
 *
 *  Authors: Alberto Wu, Michal 'GiM' Spadlinski
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2 as
 *  published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 *  MA 02110-1301, USA.
 */

#if HAVE_CONFIG_H
#include "clamav-config.h"
#endif

#include "clamav.h"
#include "others.h"
#include "execs.h"
#include "pe.h"
#include "packlibs.h"

static int doubledl(const char **scur, uint8_t *mydlptr, const char *buffer, uint32_t buffersize)
{
    unsigned char mydl  = *mydlptr;
    unsigned char olddl = mydl;

    mydl *= 2;
    if (!(olddl & 0x7f)) {
        if (*scur < buffer || *scur >= buffer + buffersize - 1)
            return -1;
        olddl = **scur;
        mydl  = olddl * 2 + 1;
        *scur = *scur + 1;
    }
    *mydlptr = mydl;
    return (olddl >> 7) & 1;
}

int cli_unfsg(const char *source, char *dest, int ssize, int dsize, const char **endsrc, char **enddst)
{
    uint8_t mydl = 0x80;
    uint32_t backbytes, backsize, oldback = 0;
    const char *csrc = source;
    char *cdst       = dest;
    int oob, lostbit = 1;

    if (ssize <= 0 || dsize <= 0) return -1;
    *cdst++ = *csrc++;

    while (1) {
        if ((oob = doubledl(&csrc, &mydl, source, ssize))) {
            if (oob == -1)
                return -1;
            /* 164 */
            backsize = 0;
            if ((oob = doubledl(&csrc, &mydl, source, ssize))) {
                if (oob == -1)
                    return -1;
                /* 16a */
                backbytes = 0;
                if ((oob = doubledl(&csrc, &mydl, source, ssize))) {
                    if (oob == -1)
                        return -1;
                    /* 170 */
                    lostbit = 1;
                    backsize++;
                    backbytes = 0x10;
                    while (backbytes < 0x100) {
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                        backbytes = backbytes * 2 + oob;
                    }
                    backbytes &= 0xff;
                    if (!backbytes) {
                        if (cdst >= dest + dsize)
                            return -1;
                        *cdst++ = 0x00;
                        continue;
                    }
                } else {
                    /* 18f */
                    if (csrc >= source + ssize)
                        return -1;
                    backbytes = *(unsigned char *)csrc;
                    backsize  = backsize * 2 + (backbytes & 1);
                    backbytes = (backbytes & 0xff) >> 1;
                    csrc++;
                    if (!backbytes)
                        break;
                    backsize += 2;
                    oldback = backbytes;
                    lostbit = 0;
                }
            } else {
                /* 180 */
                backsize = 1;
                do {
                    if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                        return -1;
                    backsize = backsize * 2 + oob;
                    if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                        return -1;
                } while (oob);

                backsize = backsize - 1 - lostbit;
                if (!backsize) {
                    /* 18a */
                    backsize = 1;
                    do {
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                        backsize = backsize * 2 + oob;
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                    } while (oob);

                    backbytes = oldback;
                } else {
                    /* 198 */
                    if (csrc >= source + ssize)
                        return -1;
                    backbytes = *(unsigned char *)csrc;
                    backbytes += (backsize - 1) << 8;
                    backsize = 1;
                    csrc++;
                    do {
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                        backsize = backsize * 2 + oob;
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                    } while (oob);

                    if (backbytes >= 0x7d00)
                        backsize++;
                    if (backbytes >= 0x500)
                        backsize++;
                    if (backbytes <= 0x7f)
                        backsize += 2;

                    oldback = backbytes;
                }
                lostbit = 0;
            }
            if (!CLI_ISCONTAINED(dest, dsize, cdst, backsize) || !CLI_ISCONTAINED(dest, dsize, cdst - backbytes, backsize))
                return -1;
            while (backsize--) {
                *cdst = *(cdst - backbytes);
                cdst++;
            }

        } else {
            /* 15d */
            if (cdst < dest || cdst >= dest + dsize || csrc < source || csrc >= source + ssize)
                return -1;
            *cdst++ = *csrc++;
            lostbit = 1;
        }
    }

    if (endsrc) *endsrc = csrc;
    if (enddst) *enddst = cdst;
    return 0;
}

int unmew(const char *source, char *dest, int ssize, int dsize, const char **endsrc, char **enddst)
{
    uint8_t mydl = 0x80;
    uint32_t myeax_backbytes, myecx_backsize, oldback = 0;
    const char *csrc = source;
    char *cdst       = dest;
    int oob, lostbit = 1;

    *cdst++ = *csrc++;

    while (1) {
        if ((oob = doubledl(&csrc, &mydl, source, ssize))) {
            if (oob == -1)
                return -1;
            /* 164 */
            myecx_backsize = 0;
            if ((oob = doubledl(&csrc, &mydl, source, ssize))) {
                if (oob == -1)
                    return -1;
                /* 16a */
                myeax_backbytes = 0;
                if ((oob = doubledl(&csrc, &mydl, source, ssize))) {
                    if (oob == -1)
                        return -1;
                    /* 170 */
                    lostbit = 1;
                    myecx_backsize++;
                    myeax_backbytes = 0x10;
                    while (myeax_backbytes < 0x100) {
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                        myeax_backbytes = myeax_backbytes * 2 + oob;
                    }
                    myeax_backbytes &= 0xff;
                    if (!myeax_backbytes) {
                        if (cdst >= dest + dsize)
                            return -1;
                        *cdst++ = 0x00;
                        /*cli_dbgmsg("X%02x  ", *(cdst-1)&0xff);*/
                        continue;
                    }
                } else {
                    /* 18f */
                    if (csrc >= source + ssize)
                        return -1;
                    myeax_backbytes = *(unsigned char *)csrc;
                    myecx_backsize  = myecx_backsize * 2 + (myeax_backbytes & 1);
                    myeax_backbytes = (myeax_backbytes & 0xff) >> 1;
                    csrc++;
                    if (!myeax_backbytes) {
                        /* cli_dbgmsg("\nBREAK \n"); */
                        break;
                    }
                    myecx_backsize += 2;
                    oldback = myeax_backbytes;
                    lostbit = 0;
                }
            } else {
                /* 180 */
                myecx_backsize = 1;
                do {
                    if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                        return -1;
                    myecx_backsize = myecx_backsize * 2 + oob;
                    if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                        return -1;
                } while (oob);

                myecx_backsize = myecx_backsize - 1 - lostbit;
                if (!myecx_backsize) {
                    /* 18a */
                    myecx_backsize = 1;
                    do {
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                        myecx_backsize = myecx_backsize * 2 + oob;
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                    } while (oob);

                    myeax_backbytes = oldback;
                } else {
                    /* 198 */
                    if (csrc >= source + ssize)
                        return -1;
                    myeax_backbytes = *(unsigned char *)csrc;
                    myeax_backbytes += (myecx_backsize - 1) << 8;
                    myecx_backsize = 1;
                    csrc++;
                    do {
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                        myecx_backsize = myecx_backsize * 2 + oob;
                        if ((oob = doubledl(&csrc, &mydl, source, ssize)) == -1)
                            return -1;
                    } while (oob);

                    if (myeax_backbytes >= 0x7d00)
                        myecx_backsize++;
                    if (myeax_backbytes >= 0x500)
                        myecx_backsize++;
                    if (myeax_backbytes <= 0x7f)
                        myecx_backsize += 2;

                    oldback = myeax_backbytes;
                }
                lostbit = 0;
            }
            if (!CLI_ISCONTAINED(dest, dsize, cdst, myecx_backsize) || !CLI_ISCONTAINED(dest, dsize, cdst - myeax_backbytes, myecx_backsize)) {
                cli_dbgmsg("MEW: rete: %p %d %p %d %d || %p %d %p %d %d\n", dest, dsize, cdst, myecx_backsize,
                           CLI_ISCONTAINED(dest, dsize, cdst, myecx_backsize),
                           dest, dsize, cdst - myeax_backbytes, myecx_backsize,
                           CLI_ISCONTAINED(dest, dsize, cdst - myeax_backbytes, myecx_backsize));
                return -1;
            }
            while (myecx_backsize--) {
                *cdst = *(cdst - myeax_backbytes);
                cdst++;
            }

        } else {
            /* 15d */
            if (cdst < dest || cdst >= dest + dsize || csrc < source || csrc >= source + ssize) {
                cli_dbgmsg("MEW: retf %p %p+%08x=%p, %p %p+%08x=%p\n",
                           cdst, dest, dsize, dest + dsize, csrc, source, ssize, source + ssize);
                return -1;
            }
            *cdst++ = *csrc++;
            /* cli_dbgmsg("Z%02x  ", *(cdst-1)&0xff); */
            lostbit = 1;
        }
    }

    *endsrc = csrc;
    *enddst = cdst;
    return 0;
}
