KEYS: Add invalidation support

Add support for invalidating a key - which renders it immediately invisible to
further searches and causes the garbage collector to immediately wake up,
remove it from keyrings and then destroy it when it's no longer referenced.

It's better not to do this with keyctl_revoke() as that marks the key to start
returning -EKEYREVOKED to searches when what is actually desired is to have the
key refetched.

To invalidate a key the caller must be granted SEARCH permission by the key.
This may be too strict.  It may be better to also permit invalidation if the
caller has any of READ, WRITE or SETATTR permission.

The primary use for this is to evict keys that are cached in special keyrings,
such as the DNS resolver or an ID mapper.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/security/keys/permission.c b/security/keys/permission.c
index c35b5229e3cd..5f4c00c0947d 100644
--- a/security/keys/permission.c
+++ b/security/keys/permission.c
@@ -87,20 +87,25 @@ EXPORT_SYMBOL(key_task_permission);
  * key_validate - Validate a key.
  * @key: The key to be validated.
  *
- * Check that a key is valid, returning 0 if the key is okay, -EKEYREVOKED if
- * the key's type has been removed or if the key has been revoked or
- * -EKEYEXPIRED if the key has expired.
+ * Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
+ * key is invalidated, -EKEYREVOKED if the key's type has been removed or if
+ * the key has been revoked or -EKEYEXPIRED if the key has expired.
  */
 int key_validate(struct key *key)
 {
 	struct timespec now;
+	unsigned long flags = key->flags;
 	int ret = 0;
 
 	if (key) {
+		ret = -ENOKEY;
+		if (flags & (1 << KEY_FLAG_INVALIDATED))
+			goto error;
+
 		/* check it's still accessible */
 		ret = -EKEYREVOKED;
-		if (test_bit(KEY_FLAG_REVOKED, &key->flags) ||
-		    test_bit(KEY_FLAG_DEAD, &key->flags))
+		if (flags & ((1 << KEY_FLAG_REVOKED) |
+			     (1 << KEY_FLAG_DEAD)))
 			goto error;
 
 		/* check it hasn't expired */