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.