This fixes a global out-of-bounds read access in the copy_buffer
function of the floppy driver.
The FDDEFPRM ioctl allows one to set the geometry of a disk. The sect
and head fields (unsigned int) of the floppy_drive structure are used to
compute the max_sector (int) in the make_raw_rw_request function. It is
possible to overflow the max_sector. Next, max_sector is passed to the
copy_buffer function and used in one of the memcpy calls.
An unprivileged user could trigger the bug if the device is accessible,
but requires a floppy disk to be inserted.
The patch adds the check for the .sect * .head multiplication for not
overflowing in the set_geometry function.