From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx168.postini.com [74.125.245.168]) by kanga.kvack.org (Postfix) with SMTP id 1FB6D6B0068 for ; Sat, 16 Jun 2012 05:42:29 -0400 (EDT) Received: by lahi5 with SMTP id i5so3329593lah.14 for ; Sat, 16 Jun 2012 02:42:27 -0700 (PDT) Message-ID: <4FDC54FF.3020305@openvz.org> Date: Sat, 16 Jun 2012 13:42:23 +0400 From: Konstantin Khlebnikov MIME-Version: 1.0 Subject: Re: [PATCH 3.5] c/r: prctl: less paranoid prctl_set_mm_exe_file() References: <20120616085104.14682.16723.stgit@zurg> <20120616090646.GD32029@moon> <20120616091712.GA2021@moon> In-Reply-To: <20120616091712.GA2021@moon> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Cyrill Gorcunov Cc: Andrew Morton , Kees Cook , Pavel Emelianov , "linux-kernel@vger.kernel.org" , Oleg Nesterov , "linux-mm@kvack.org" , Matt Helsley , KOSAKI Motohiro , Tejun Heo Cyrill Gorcunov wrote: > On Sat, Jun 16, 2012 at 01:06:46PM +0400, Cyrill Gorcunov wrote: >> On Sat, Jun 16, 2012 at 12:51:04PM +0400, Konstantin Khlebnikov wrote: >>> "no other files mapped" requirement from my previous patch >>> (c/r: prctl: update prctl_set_mm_exe_file() after mm->num_exe_file_vmas removal) >>> is too paranoid, it forbids operation even if there mapped one shared-anon vma. >>> >>> Let's check that current mm->exe_file already unmapped, in this case exe_file >>> symlink already outdated and its changing is reasonable. >>> >>> Plus, this patch fixes exit code in case operation success. >>> >>> Signed-off-by: Konstantin Khlebnikov >>> Reported-by: Cyrill Gorcunov >>> Cc: Oleg Nesterov >>> Cc: Matt Helsley >>> Cc: Kees Cook >>> Cc: KOSAKI Motohiro >>> Cc: Tejun Heo >>> Cc: Pavel Emelyanov >>> --- >> >> Ack! Thanks again, Konstantin! > > 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. > > Cyrill -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org