From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755426AbbAWOQa (ORCPT ); Fri, 23 Jan 2015 09:16:30 -0500 Received: from bes.se.axis.com ([195.60.68.10]:33698 "EHLO bes.se.axis.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751626AbbAWOQ2 (ORCPT ); Fri, 23 Jan 2015 09:16:28 -0500 Date: Fri, 23 Jan 2015 15:16:23 +0100 From: Jonas Danielsson To: CC: , , , , , , , , , , , , , Subject: Regression introduced by commit dbe9a4173ea53 Message-ID: <20150123141623.GK30451@lnxjonasdn.se.axis.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I have seen a regression, that I think is caused by: commit dbe9a4173ea53b72b2c35d19f676a85b69f1c9fe Author: Eric W. Biederman Date: Thu Sep 6 18:20:01 2012 +0000 scm: Don't use struct ucred in NETLINK_CB and struct scm_cookie. With this commit the value send as uid when credentials are missing changes from -1 to overflowuid (default -2, the 'nobody' user). I was using dbus-send to perform a method call on a gdbus server. And sometimes I fall victim to the race condition caused by: commit 16e5726 ("af_unix: dont send SCM_CREDENTIALS by default") And then there will be no credentials on the socket. The glib library checks the uid, and if it is -1, it will fall back to using SO_PEERCRED and things will work for me. But since the commit in $subject changes the uid I get failure with NoReply from dbus-send. It seems that before the commit in $subject that the function from_kuid_munged was only called if there were credentials present. Otherwise we would set uid to -1. Now uid gets set to -1 if there is no credentials but from_kuid_munged is always called. And from the documentation of from_kuid_munged it states that it 'never fails and always returns a valid uid'. And in the case of uid being -1, it returns overflowuid. So this seems like it broke glib. Caused by 1) the introduced race condition that makes it not totally safe to set SO_PEERCRED on the accepted socket and 2) that the value of uid when credentials are missing changed from -1 to overflowuid. Thanks for your time Jonas