Toddler's Bottle - fd

1. User is required to provide a argv.
2. A calculation is made to get fd.
3. Read action: read 32 bytes from fd into buf.
4. You get the flag if buf == LETMEWIN\n

What's is fd?

1. fd == 0 is stdin
2. fd == 1 is stdout
3. fd == 2 is stderr

code:

char buf[32];
int main(int argc, char* argv[], char* envp[]){
    if(argc<2){
        printf("pass argv[1] a number\n");
        return 0;
    }
    int fd = atoi( argv[1] ) - 0x1234;
    int len = 0;
    len = read(fd, buf, 32);
    if(!strcmp("LETMEWIN\n", buf)){
        printf("good job :)\n");
        system("/bin/cat flag");
        exit(0);
    }
    printf("learn about Linux file IO\n");
    return 0;

}

Solution:

Make fd 0, so argv should be 0x1234(4660 in decimal)

fd@ubuntu:~$ ./fd 4660
LETMEWIN
good job :)
mommy! I think I know what a file descriptor is!!

OR

echo "LETMEWIN" | ./fd 4660
good job :)
mommy! I think I know what a file descriptor is!!