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 <[e-mail]>
Acked-by: Mike Rapoport (Microsoft) <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Ira Weiny <[e-mail]>

drivers/nvdimm/ramdax.c

···
 		return -EINVAL;
 	if (struct_size(cmd, out_buf, cmd->in_length) > buf_len)
 		return -EINVAL;
-	if (cmd->in_offset + cmd->in_length > LABEL_AREA_SIZE)
+	if (size_add(cmd->in_offset, cmd->in_length) > LABEL_AREA_SIZE)
 		return -EINVAL;
 
 	memcpy(cmd->out_buf, dimm->label_area + cmd->in_offset, cmd->in_length);
···
 		return -EINVAL;
 	if (struct_size(cmd, in_buf, cmd->in_length) > buf_len)
 		return -EINVAL;
-	if (cmd->in_offset + cmd->in_length > LABEL_AREA_SIZE)
+	if (size_add(cmd->in_offset, cmd->in_length) > LABEL_AREA_SIZE)
 		return -EINVAL;
 
 	memcpy(dimm->label_area + cmd->in_offset, cmd->in_buf, cmd->in_length);