[S390] cio: fix potential overflow in chpid descriptor

The length filed in the chsc response block (if valid)
has a value of n*(sizeof(chp_desc))+8 (for the response
block header). When we memcopied from the response block
to the actual descriptor we copied 8 bytes too much.
The bug was not revealed since the descriptor is embedded
in struct channel_path.
Since we only write one descriptor at a time ignore the
length value and use sizeof(*desc).
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/cio/chsc.c

@@ -713,7 +713,7 @@ int chsc_determine_base_channel_path_desc(struct chp_id chpid,
 	ret = chsc_determine_channel_path_desc(chpid, 0, 0, 0, 0, chsc_resp);
 	if (ret)
 		goto out_free;
-	memcpy(desc, &chsc_resp->data, chsc_resp->length);
+	memcpy(desc, &chsc_resp->data, sizeof(*desc));
 out_free:
 	kfree(chsc_resp);
 	return ret;