From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752513Ab2CEVOz (ORCPT ); Mon, 5 Mar 2012 16:14:55 -0500 Received: from e1.ny.us.ibm.com ([32.97.182.141]:42462 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751337Ab2CEVOy (ORCPT ); Mon, 5 Mar 2012 16:14:54 -0500 Date: Mon, 5 Mar 2012 13:14:36 -0800 From: Matt Helsley To: Oleg Nesterov Cc: Andrew Morton , Matt Helsley , Alexey Dobriyan , Cyrill Gorcunov , "Eric W. Biederman" , Kees Cook , KOSAKI Motohiro , Pavel Emelyanov , Tejun Heo , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/1] turn mm->exe_file into mm->exe_path Message-ID: <20120305211436.GM7666@count0.beaverton.ibm.com> References: <20120305152826.GA12419@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120305152826.GA12419@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12030521-6078-0000-0000-000008BC32A3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 05, 2012 at 04:28:26PM +0100, Oleg Nesterov wrote: > I think the patch is simple and self-explanatory, it simply > does s/mm->exe_file/mm->exe_path/. > > Why do we need mm->exe_file? IIUC, there are 2 reasons: > > 1. we do not want O(n) proc/pid/exe looking for the 1st > VM_EXECUTABLE vma. (Frankly this always seemed like a bit of a hack to me. If someone got creative with text layout then it could break this hack...) > > 2. we do not want to rely on vma->vm_file->f_path, > bprm->file->f_op->mmap can change ->vm_file. > > Unless there was another subtle reason, "struct path *exe_path" > can equally work but it looks more clear. PATCH 1/1 looks fine. I think Alexey Dobriyan was working on a similar patch years ago. > And can't we also remove added_exe_file_vma/removed_exe_file_vma? > Why do we need mm->num_exe_file_vmas? Afaics it is only needed to > "free" mm->exe_file if the application unmaps all these vmas. Say, > to allow to unmount fs. Yup. I know it's not pretty to have to track the exe file refs this way but I couldn't see any other way to keep a reference to the file (or path) and avoid pinning the mounted filesystem the exectuable is on. > Can't we simply add PR_CLEAR_MM_EXE_PATH instead? Of course it is > not enough if ->vm_file still has a reference. But c/r people want Relying solely on this prctl would break existing programs. I believe Al Viro's example was a program that copies its text to a new executable area, unmaps the original, performs a pivot_root(), and finally umounts the old root. Removing the counter would cause the mount to be pinned for these programs and the umount would fail. > PR_SET_MM_EXE_FILE anyway, see http://marc.info/?t=133052865500016 > So perhaps we can add PR_SET_MM_EXE_PATH which accepts NULL as well > and kill this counter? > > Oleg. Cheers, -Matt Helsley