59 lines
1.7 KiB
C
59 lines
1.7 KiB
C
#include <unistd.h>
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#include <stdio.h>
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#include <stdlib.h>
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int main(void) {
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unsigned int *chunk;
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int i;
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unsigned int shellcode[10];
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unsigned int ret_addr_2_change = 9;
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/* Get some space */
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chunk = malloc(0x8);
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/* now setup the chunk to fool chunk_free()
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By making prev_size negative it will look
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_after_ this chunk in stead of in front of it
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*/
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chunk[0] = -0x10; /* prev_size */
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chunk[1] = 0x8; /* size */
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chunk[2] = shellcode; /* fd */
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chunk[3] = shellcode; /* bk */
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/* set fd to the adres of the return address - 3
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the minus 3 is needed because fd[3] will become bk
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bk will be set to point to our shellcode. Remember that
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bk[2] will be changed to contain fd so that there should be
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a jmp or so in the shellcode to skip that value.
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*/
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chunk[4+2] = (int) (&ret_addr_2_change - 3);
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chunk[4+3] = (int) (shellcode);
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/* set shellcode to 0 so that we can see the change */
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memset(shellcode, 0, sizeof(shellcode));
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i = ret_addr_2_change;
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// printf("ret before call: %x\n", ret_addr_2_change);
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// printf("address of ret: %x\n", &ret_addr_2_change);
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// printf("address of shellcode: %x\n", shellcode);
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/* remember we give mem to free which finds the chunk based on
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that */
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free(chunk+2);
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// printf("ret now: %x\n", ret_addr_2_change);
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if (ret_addr_2_change != i) {
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printf("FAIL\n"); /* Exploit succeeded */
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exit(1);
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}
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for (i = 0 ; i < 10; i++) {
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if (shellcode[i] != 0) {
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printf("FAIL\n"); /* Exploit succeeded */
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exit(1);
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}
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}
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return 0;
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}
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