keys: Reuse keyring_index_key::desc_len in lookup_user_key()

When lookup_user_key() checks whether the key is possessed, it should
use the key's existing index_key including the 'desc_len' field, rather
than recomputing the 'desc_len'.  This doesn't change the behavior; this
way is just simpler and faster.
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Reviewed-by: NJames Morris <jamorris@linux.microsoft.com>

security/keys/process_keys.c

@@ -688,9 +688,7 @@ key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
 		key_ref = make_key_ref(key, 0);
 
 		/* check to see if we possess the key */
-		ctx.index_key.type		= key->type;
-		ctx.index_key.description	= key->description;
-		ctx.index_key.desc_len		= strlen(key->description);
+		ctx.index_key			= key->index_key;
 		ctx.match_data.raw_data		= key;
 		kdebug("check possessed");
 		skey_ref = search_process_keyrings(&ctx);