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, 6 insertions, 16 deletions

diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index bc9af551fc83..e49d1de0614e 100644
--- a/include/linux/key-type.h
+++ b/include/linux/key-type.h
@@ -21,15 +21,6 @@ struct kernel_pkey_query;
 struct kernel_pkey_params;
 
 /*
- * key under-construction record
- * - passed to the request_key actor if supplied
- */
-struct key_construction {
-	struct key	*key;	/* key being constructed */
-	struct key	*authkey;/* authorisation for key being constructed */
-};
-
-/*
  * Pre-parsed payload, used by key add, update and instantiate.
  *
  * This struct will be cleared and data and datalen will be set with the data
@@ -50,8 +41,7 @@ struct key_preparsed_payload {
 	time64_t	expiry;		/* Expiry time of key */
 } __randomize_layout;
 
-typedef int (*request_key_actor_t)(struct key_construction *key,
-				   const char *op, void *aux);
+typedef int (*request_key_actor_t)(struct key *auth_key, void *aux);
 
 /*
  * Preparsed matching criterion.
@@ -181,20 +171,20 @@ extern int key_instantiate_and_link(struct key *key,
 				    const void *data,
 				    size_t datalen,
 				    struct key *keyring,
-				    struct key *instkey);
+				    struct key *authkey);
 extern int key_reject_and_link(struct key *key,
 			       unsigned timeout,
 			       unsigned error,
 			       struct key *keyring,
-			       struct key *instkey);
-extern void complete_request_key(struct key_construction *cons, int error);
+			       struct key *authkey);
+extern void complete_request_key(struct key *authkey, int error);
 
 static inline int key_negate_and_link(struct key *key,
 				      unsigned timeout,
 				      struct key *keyring,
-				      struct key *instkey)
+				      struct key *authkey)
 {
-	return key_reject_and_link(key, timeout, ENOKEY, keyring, instkey);
+	return key_reject_and_link(key, timeout, ENOKEY, keyring, authkey);
 }
 
 extern int generic_key_instantiate(struct key *key, struct key_preparsed_payload *prep);