nvdimm: Prevent integer overflow in ramdax_get_config_data()

nvdimm: Prevent integer overflow in ramdax_get_config_data()

The "cmd->in_offset" variable comes from the user via the __nd_ioctl()
function.  The problem is that the "cmd->in_offset + cmd->in_length"
addition could have an integer wrapping issue if cmd->in_offset is close
to UINT_MAX .  Both "cmd->in_offset" and "cmd->in_length" are u32
variables.

Fixes: 43bc0aa19a21 ("nvdimm: allow exposing RAM carveouts as NVDIMM DIMM devices")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Link: https://patch.msgid.link/aSbuiYCznEIZDa02@stanley.mountain
Signed-off-by: Ira Weiny <ira.weiny@intel.com>