Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751216AbdFDGxO (ORCPT ); Sun, 4 Jun 2017 02:53:14 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:53976 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750852AbdFDGxB (ORCPT ); Sun, 4 Jun 2017 02:53:01 -0400 Date: Sun, 4 Jun 2017 07:51:30 +0100 From: Al Viro To: Matt Brown Cc: james.l.morris@oracle.com, serge@hallyn.com, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: Re: [PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM Message-ID: <20170604065118.GL6365@ZenIV.linux.org.uk> References: <20170603055351.16080-1-matt@nmatt.com> <20170603063354.GJ6365@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.8.0 (2017-02-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1417 Lines: 34 On Sun, Jun 04, 2017 at 01:24:13AM -0400, Matt Brown wrote: > On 06/03/2017 02:33 AM, Al Viro wrote: > > On Sat, Jun 03, 2017 at 01:53:51AM -0400, Matt Brown wrote: > > > > > +static int tpe_bprm_set_creds(struct linux_binprm *bprm) > > > +{ > > > + struct file *file = bprm->file; > > > + struct inode *inode = d_backing_inode(file->f_path.dentry->d_parent); > > > + struct inode *file_inode = d_backing_inode(file->f_path.dentry); > > > > Bloody wonderful. Do tell, what *does* prevent a race with rename(2) here, > > somehow making sure that your 'inode' won't get freed right under you? > > > > Good catch. How does this look: > > spin_lock(&inode->i_lock); > spin_lock(&file_inode->i_lock); > if (global_nonroot(inode->i_uid) && !uid_eq(inode->i_uid, cred->uid)) > reason1 = "directory not owned by user"; > else if (inode->i_mode & 0002) > reason1 = "file in world-writable directory"; > else if ((inode->i_mode & 0020) && global_nonroot_gid(inode->i_gid)) > reason1 = "file in group-writable directory"; > else if (file_inode->i_mode & 0002) > reason1 = "file is world-writable"; > spin_unlock(&inode->i_lock); > spin_unlock(&file_inode->i_lock); > > and likewise for other places in the code? Er... You have a pointer to object that might get freed by a thread running on another CPU. So you attempt to take a spinlock sitting inside that object. How exactly is that supposed to help anything?