scsi: arcmsr: Buffer overflow in arcmsr_iop_message_xfer()

[ Upstream commit 7bc2b55a ]

We need to put an upper bound on "user_len" so the memcpy() doesn't
overflow.

References: CVE-2016-7425
Cc: <stable@vger.kernel.org>
Reported-by: Marco Grassi <marco.gra@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Philipp Hahn <hahn@univention.de>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>