From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756044AbcHVQ1R (ORCPT ); Mon, 22 Aug 2016 12:27:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34246 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755602AbcHVQ1Q (ORCPT ); Mon, 22 Aug 2016 12:27:16 -0400 Date: Mon, 22 Aug 2016 18:27:09 +0200 From: Mateusz Guzik To: Richard Guy Briggs Cc: linux-audit@redhat.com, linux-kernel@vger.kernel.org, ebiederm@xmission.com, oleg@redhat.com, skinsbursky@virtuozzo.com, luto@amacapital.net, sgrubb@redhat.com, pmoore@redhat.com, eparis@redhat.com Subject: Re: [PATCH] audit: fix audit_exe_compare using get_mm_exe_file Message-ID: <20160822162708.5ohk6h247ye76fin@mguzik> References: <843cd1056b76a3c28585e5b6d711fe53d4f78c18.1471879964.git.rgb@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <843cd1056b76a3c28585e5b6d711fe53d4f78c18.1471879964.git.rgb@redhat.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 22 Aug 2016 16:27:16 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 22, 2016 at 11:41:34AM -0400, Richard Guy Briggs wrote: > Fix original naive attempt to get/lock access to task->mm->exe_file by > using get_mm_exe_file and checking for NULL. > > See: https://lkml.org/lkml/2016/7/30/97 > > Signed-off-by: Richard Guy Briggs > --- > kernel/audit_watch.c | 13 ++++++++++--- > 1 files changed, 10 insertions(+), 3 deletions(-) > > diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c > index d6709eb..0b29279 100644 > --- a/kernel/audit_watch.c > +++ b/kernel/audit_watch.c > @@ -19,6 +19,7 @@ > * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA > */ > > +#include > #include > #include > #include > @@ -540,14 +541,20 @@ int audit_dupe_exe(struct audit_krule *new, struct audit_krule *old) > > int audit_exe_compare(struct task_struct *tsk, struct audit_fsnotify_mark *mark) > { > + struct mm_struct *mm; > struct file *exe_file; > unsigned long ino; > dev_t dev; > > - rcu_read_lock(); > - exe_file = rcu_dereference(tsk->mm->exe_file); > + mm = get_task_mm(tsk); > + if (!mm) > + return 0; > + exe_file = get_mm_exe_file(mm); > + mmput(mm); > + if (!exe_file) > + return 0; > ino = exe_file->f_inode->i_ino; > dev = exe_file->f_inode->i_sb->s_dev; > - rcu_read_unlock(); > + fput(exe_file); > return audit_mark_compare(mark, ino, dev); > } I think this works but I have a better idea. This basically duplicates a part of proc_exe_link and does unnecessary work. Instead, one can introduce get_task_exe_file. task_lock held guarantees the stability of mm struct itself, and then we can we can try to grab the file without mm refcount dance. I'll implement this later today. -- Mateusz Guzik