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: 43bc0aa ("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>

Author: Dan Carpenter

drivers/nvdimm/ramdax.c

@@ -143,7 +143,7 @@ static int ramdax_get_config_data(struct nvdimm *nvdimm, int buf_len,
 		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);
@@ -160,7 +160,7 @@ static int ramdax_set_config_data(struct nvdimm *nvdimm, int buf_len,
 		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);