Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756191Ab2FPJrU (ORCPT ); Sat, 16 Jun 2012 05:47:20 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:40004 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753951Ab2FPJrT (ORCPT ); Sat, 16 Jun 2012 05:47:19 -0400 Date: Sat, 16 Jun 2012 13:47:14 +0400 From: Cyrill Gorcunov To: Konstantin Khlebnikov Cc: Andrew Morton , Kees Cook , Pavel Emelianov , "linux-kernel@vger.kernel.org" , Oleg Nesterov , "linux-mm@kvack.org" , Matt Helsley , KOSAKI Motohiro , Tejun Heo Subject: Re: [PATCH 3.5] c/r: prctl: less paranoid prctl_set_mm_exe_file() Message-ID: <20120616094714.GF32029@moon> References: <20120616085104.14682.16723.stgit@zurg> <20120616090646.GD32029@moon> <20120616091712.GA2021@moon> <4FDC54FF.3020305@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FDC54FF.3020305@openvz.org> 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 Content-Length: 1913 Lines: 44 On Sat, Jun 16, 2012 at 01:42:23PM +0400, Konstantin Khlebnikov wrote: > >Side note: there is a little nit with this patch actually, > >because while when we do c/r we do "right things" and unmap > >all vm-executable mappings before we set up new exe_file. But > >we can't guarantee that some brave soul would not setup > >new exe-file just for it's own, then what we migh have > > > > - mm::exe_file set up and points to some file, moreover num_exe_file_vmas might be> 1 > > - application calls for prctl_set_mm_exe_file > > - set_mm_exe_file(mm, exe_file) called, and it drops num_exe_file_vmas to 0 > > - finally application might call for removed_exe_file_vma > > > >void removed_exe_file_vma(struct mm_struct *mm) > >{ > > mm->num_exe_file_vmas--; > > if ((mm->num_exe_file_vmas == 0)&& mm->exe_file) { > > fput(mm->exe_file); > > mm->exe_file = NULL; > > } > > > >} > > > >and it does _not_ test for num_exe_file_vmas being 0 before doing decrement, > >thus we get inconsistency in counter. > > No, removed_exe_file_vma() is called only for vma with VM_EXECUTABLE flag, > there no way to get such vma other than sys_execve(). > And this brave soul cannot call prctl_set_mm_exe_file() successfully, > just because for vma with VM_EXECUTABLE flag vma->vm_file == mm->exe_file. > > Anyway, I plan to get rid of mm->num_exe_file_vmas and VM_EXECUTABLE. Yeah, you've changed !path_equal to path_equal. And yes, getting rid of num_exe_file_vmas is good idea. Btw, Konstantin, why do we need to call for path_equal? Maybe we can simply test for mm->exe_file == NULL, and refuse to change anything if it's not nil value? This will simplify the code. Cyrill -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/