block: fix overflow in blk_ioctl_discard()

In the Linux kernel, the following vulnerability has been resolved: block: fix overflow in blk_ioctl_discard() There is no check for overflow of 'start + len' in blk_ioctl_discard(). Hung task occurs if submit an discard ioctl with the following param: start = 0x80000000000ff000, len = 0x8000000000fff000; Add the overflow validation now.