uml: check length in exitcode_proc_write()

We don't cap the size of buffer from the user so we could write past the
end of the array here.  Only root can write to this file.

Reported-by: Nico Golde <nico@ngolde.de>
Reported-by: Fabian Yamaguchi <fabs@goesec.de>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
static int make_proc_exitcode(void)
{
	struct proc_dir_entry *ent;

	ent = proc_create("exitcode", 0600, NULL, &exitcode_proc_fops);
	if (ent == NULL) {
		printk(KERN_WARNING "make_proc_exitcode : Failed to register "
		       "/proc/exitcode\n");
		return 0;
	}
	return 0;
}

static int make_proc_exitcode(void)
{
	struct proc_dir_entry *ent;

	ent = proc_create("exitcode", 0600, NULL, &exitcode_proc_fops);
	if (ent == NULL) {
		printk(KERN_WARNING "make_proc_exitcode : Failed to register "
		       "/proc/exitcode\n");
		return 0;
	}
	return 0;
}
