From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755415AbZGAT1b (ORCPT ); Wed, 1 Jul 2009 15:27:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754054AbZGAT1X (ORCPT ); Wed, 1 Jul 2009 15:27:23 -0400 Received: from mx2.redhat.com ([66.187.237.31]:32892 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752297AbZGAT1W (ORCPT ); Wed, 1 Jul 2009 15:27:22 -0400 Message-ID: <4A4BB898.10909@redhat.com> Date: Wed, 01 Jul 2009 14:27:20 -0500 From: Eric Sandeen User-Agent: Thunderbird 2.0.0.22 (Macintosh/20090605) MIME-Version: 1.0 To: Amerigo Wang CC: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Eugene Teo , viro@zeniv.linux.org.uk, Eric Paris Subject: Re: [Patch] allow file truncations when both suid and write permissions set References: <20090625090146.6616.9720.sendpatchset@localhost.localdomain> <4A4BA6F8.7090905@redhat.com> In-Reply-To: <4A4BA6F8.7090905@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Eric Sandeen wrote: > Amerigo Wang wrote: >> When suid is set and the non-owner user has write permission, >> any writing into this file should be allowed and suid should be >> removed after that. >> >> However, current kernel only allows writing without truncations, >> when we do truncations on that file, we get EPERM. This is a bug. ... > So I think the main problem here is simply that we didn't set > ATTR_FORCE, right... > > Seems a little odd to |= with ret, -then- check if it's non-0. Maybe: > > /* Remove suid/sgid on truncate too */ > - newattrs.ia_valid |= should_remove_suid(dentry); > + ret = should_remove_suid(dentry); > + if (ret) > + newattrs.ia_valid |= (ret | ATTR_FORCE); > On second thought, and after talking w/ eparis, I think this probably needs a security_inode_killpriv() too... it seems like it might be best to change file_remove_suid(*file) to dentry_remove_suid(*dentry) and just call that from do_truncate()? -Eric