crystal, 79 bytes

Result

AC

Duration

1850ms

Code [DL]

h,w=STDIN.each_line.map(&.to_i).to_a;puts q="*"*w,("*"+" "*(w-2)+"*\n")*(h-2),q

stdin

24
15

stdout

***************
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
*             *
***************

stderr