keys: Fix dependency loop between construction record and auth key

In the request_key() upcall mechanism there's a dependency loop by which if
a key type driver overrides the ->request_key hook and the userspace side
manages to lose the authorisation key, the auth key and the internal
construction record (struct key_construction) can keep each other pinned.

Fix this by the following changes:

 (1) Killing off the construction record and using the auth key instead.

 (2) Including the operation name in the auth key payload and making the
     payload available outside of security/keys/.

 (3) The ->request_key hook is given the authkey instead of the cons
     record and operation name.

Changes (2) and (3) allow the auth key to naturally be cleaned up if the
keyring it is in is destroyed or cleared or the auth key is unlinked.

Fixes: 7ee02a316600 ("keys: Fix dependency loop between construction record and auth key")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <james.morris@microsoft.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/include/keys/request_key_auth-type.h b/include/keys/request_key_auth-type.h
new file mode 100644
index 000000000000..a726dd3f1dc6
--- /dev/null
+++ b/include/keys/request_key_auth-type.h
@@ -0,0 +1,36 @@
+/* request_key authorisation token key type
+ *
+ * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#ifndef _KEYS_REQUEST_KEY_AUTH_TYPE_H
+#define _KEYS_REQUEST_KEY_AUTH_TYPE_H
+
+#include <linux/key.h>
+
+/*
+ * Authorisation record for request_key().
+ */
+struct request_key_auth {
+	struct key		*target_key;
+	struct key		*dest_keyring;
+	const struct cred	*cred;
+	void			*callout_info;
+	size_t			callout_len;
+	pid_t			pid;
+	char			op[8];
+} __randomize_layout;
+
+static inline struct request_key_auth *get_request_key_auth(const struct key *key)
+{
+	return key->payload.data[0];
+}
+
+
+#endif /* _KEYS_REQUEST_KEY_AUTH_TYPE_H */