KEYS: Add a key type op to permit the key description to be vetted

Add a key type operation to permit the key type to vet the description of a new
key that key_alloc() is about to allocate.  The operation may reject the
description if it wishes with an error of its choosing.  If it does this, the
key will not be allocated.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/security/keys/key.c b/security/keys/key.c
index 1c2d43d..8e315ef 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -249,6 +249,14 @@
 	if (!desc || !*desc)
 		goto error;
 
+	if (type->vet_description) {
+		ret = type->vet_description(desc);
+		if (ret < 0) {
+			key = ERR_PTR(ret);
+			goto error;
+		}
+	}
+
 	desclen = strlen(desc) + 1;
 	quotalen = desclen + type->def_datalen;