scsi: megaraid_sas: Check user-provided offsets

commit 381d34e376e3d9d27730fda8a0e870600e6c8196 upstream.

It sounds unwise to let user space pass an unchecked 32-bit offset into a
kernel structure in an ioctl. This is an unsigned variable, so checking the
upper bound for the size of the structure it points into is sufficient to
avoid data corruption, but as the pointer might also be unaligned, it has
to be written carefully as well.

While I stumbled over this problem by reading the code, I did not continue
checking the function for further problems like it.

Link: https://lore.kernel.org/r/20201030164450.1253641-2-arnd@kernel.org


Fixes: c4a3e0a5 ("[SCSI] MegaRAID SAS RAID: new driver")
Cc: <stable@vger.kernel.org> # v2.6.15+
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>