KEYS: fix key refcount leak in keyctl_assume_authority()

From: Eric Biggers <[email protected]>

In keyctl_assume_authority(), if keyctl_change_reqkey_auth() were to fail, we would leak the reference to the 'authkey'. Currently this can only happen if prepare_creds() fails to allocate memory. But it still should be fixed, as it is a more severe bug waiting to happen.

This patch also moves the read of 'authkey->serial' to before the reference to the authkey is dropped. Doing the read after dropping the reference is very fragile because it assumes we still hold another reference to the key. (Which we do, in current->cred->request_key_auth, but there's no reason not to write it in the "obviously correct" way.)

---
 security/keys/keyctl.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

index 6a82090c7fc1..552e4460683b 100644
@@ -1411,11 +1411,9 @@ long keyctl_assume_authority(key_serial_t id)
 	}
 
 	ret = keyctl_change_reqkey_auth(authkey);
-	if (ret < 0)
-		goto error;
+	if (ret = 0)
+		ret = authkey->serial;
 	key_put(authkey);
-
-	ret = authkey->serial;
 error:
 	return ret;
 }

2.14.1.690.gbb1197296e-goog