[PATCH] keys: discard the contents of a key on revocation

Cause the keys linked to a keyring to be unlinked from it when revoked and it
causes the data attached to a user-defined key to be discarded when revoked.

This frees up most of the quota a key occupied at that point, rather than
waiting for the key to actually be destroyed.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/keys/user-type.h

@@ -37,6 +37,7 @@ extern struct key_type key_type_user;
 extern int user_instantiate(struct key *key, const void *data, size_t datalen);
 extern int user_update(struct key *key, const void *data, size_t datalen);
 extern int user_match(const struct key *key, const void *criterion);
+extern void user_revoke(struct key *key);
 extern void user_destroy(struct key *key);
 extern void user_describe(const struct key *user, struct seq_file *m);
 extern long user_read(const struct key *key,

security/keys/keyring.c

@@ -49,6 +49,7 @@ static inline unsigned keyring_hash(const char *desc)
 static int keyring_instantiate(struct key *keyring,
 			       const void *data, size_t datalen);
 static int keyring_match(const struct key *keyring, const void *criterion);
+static void keyring_revoke(struct key *keyring);
 static void keyring_destroy(struct key *keyring);
 static void keyring_describe(const struct key *keyring, struct seq_file *m);
 static long keyring_read(const struct key *keyring,
@@ -59,6 +60,7 @@ struct key_type key_type_keyring = {
 	.def_datalen	= sizeof(struct keyring_list),
 	.instantiate	= keyring_instantiate,
 	.match		= keyring_match,
+	.revoke		= keyring_revoke,
 	.destroy	= keyring_destroy,
 	.describe	= keyring_describe,
 	.read		= keyring_read,
@@ -953,3 +955,22 @@ int keyring_clear(struct key *keyring)
 } /* end keyring_clear() */
 
 EXPORT_SYMBOL(keyring_clear);
+
+/*****************************************************************************/
+/*
+ * dispose of the links from a revoked keyring
+ * - called with the key sem write-locked
+ */
+static void keyring_revoke(struct key *keyring)
+{
+	struct keyring_list *klist = keyring->payload.subscriptions;
+
+	/* adjust the quota */
+	key_payload_reserve(keyring, 0);
+
+	if (klist) {
+		rcu_assign_pointer(keyring->payload.subscriptions, NULL);
+		call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
+	}
+
+} /* end keyring_revoke() */

security/keys/user_defined.c

@@ -28,6 +28,7 @@ struct key_type key_type_user = {
 	.instantiate	= user_instantiate,
 	.update		= user_update,
 	.match		= user_match,
+	.revoke		= user_revoke,
 	.destroy	= user_destroy,
 	.describe	= user_describe,
 	.read		= user_read,
@@ -67,6 +68,7 @@ error:
 	return ret;
 
 } /* end user_instantiate() */
+
 EXPORT_SYMBOL_GPL(user_instantiate);
 
 /*****************************************************************************/
@@ -141,7 +143,28 @@ EXPORT_SYMBOL_GPL(user_match);
 
 /*****************************************************************************/
 /*
- * dispose of the data dangling from the corpse of a user
+ * dispose of the links from a revoked keyring
+ * - called with the key sem write-locked
+ */
+void user_revoke(struct key *key)
+{
+	struct user_key_payload *upayload = key->payload.data;
+
+	/* clear the quota */
+	key_payload_reserve(key, 0);
+
+	if (upayload) {
+		rcu_assign_pointer(key->payload.data, NULL);
+		call_rcu(&upayload->rcu, user_update_rcu_disposal);
+	}
+
+} /* end user_revoke() */
+
+EXPORT_SYMBOL(user_revoke);
+
+/*****************************************************************************/
+/*
+ * dispose of the data dangling from the corpse of a user key
  */
 void user_destroy(struct key *key)
 {