Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932917Ab1D0Pmr (ORCPT ); Wed, 27 Apr 2011 11:42:47 -0400 Received: from mail-wy0-f174.google.com ([74.125.82.174]:36194 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932231Ab1D0Pmp (ORCPT ); Wed, 27 Apr 2011 11:42:45 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:content-transfer-encoding :in-reply-to:user-agent; b=CuAJ/e2UgQlz2T0/B30Q985ilTEng6sl5F/yJtRkl+WmGUkqW5nNGis4mgoP4KuhAQ P9CbrCI2Uz0dd7OIfDF3nhmvomuWlelNnyVYu4epLTyVDF6IIeV5kswaUfs+G6yYsbKV W1iekRT0gfTlckU1wLIkNtVQ6kyDuOOYqiyfw= Date: Wed, 27 Apr 2011 17:42:39 +0200 From: Andrea Righi To: Mike Frysinger Cc: Dave Chinner , Andrew Morton , Al Viro , Arnd Bergmann , linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] [PATCH] drop_pagecache syscall Message-ID: <20110427154238.GC15335@linux.betterlinux.com> References: <1303853727-21444-1-git-send-email-andrea@betterlinux.com> <20110427001453.GD12436@dastard> <20110427085910.GA1749@linux.betterlinux.com> <20110427094717.GB1749@linux.betterlinux.com> <20110427095709.GA1687@linux.develer.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2667 Lines: 53 On Wed, Apr 27, 2011 at 11:25:47AM -0400, Mike Frysinger wrote: > On Wed, Apr 27, 2011 at 05:57, Andrea Righi wrote: > > On Wed, Apr 27, 2011 at 05:50:04AM -0400, Mike Frysinger wrote: > >> On Wed, Apr 27, 2011 at 05:47, Andrea Righi wrote: > >> > On Wed, Apr 27, 2011 at 05:10:41AM -0400, Mike Frysinger wrote: > >> >> On Wed, Apr 27, 2011 at 05:01, Andrea Righi wrote: > >> >> > On Wed, Apr 27, 2011 at 10:14:53AM +1000, Dave Chinner wrote: > >> >> >> On Tue, Apr 26, 2011 at 11:35:27PM +0200, Andrea Righi wrote: > >> >> >> > This functionality can be used by all the applications that want to have a > >> >> >> > better control over the page cache management (for example to immediately drop > >> >> >> > pages that for sure will not be reused in the near future, without calling > >> >> >> > posix_fadvise() for all the files they've touched), or to provide a more fine > >> >> >> > grained debugging feature usable by the filesystem benchmarks. > >> >> >> > > >> >> >> > The system call does not require root privileges and it can be called by any > >> >> >> > unprivileged application. For example, we can write a userspace tool to run > >> >> >> > something like this: > >> >> >> > > >> >> >> > ? $ drop-pagecache /path/file_or_dir > >> >> >> > >> >> >> That's a potential DOS vector, I think. Drop the pagecache in a hard > >> >> >> loop on the root fs of a busy server and watch it crawl... > >> >> > > >> >> > Yes, probably we could allow only the CAP_SYS_ADMIN tasks to execute > >> >> > this syscall. > >> >> > >> >> if /proc/sys/vm/drop_caches has any checks other than file permission > >> >> checks (i.e. UID==0), it'd probably be better to copy those rather > >> >> than picking something different. > >> > > >> > ok, what about checking current_euid() == 0? > >> > >> that's not what i meant. ?if the drop_caches file already has certain > >> cap checks/whatever in place, let's use those. ?if it doesnt, then > >> picking a cap level as you proposed makes sense. > > > > mmh, drop_caches has a file ownership (root:root) and a permission mask > > (0644), how to apply the same checks to a system call? The most similar > > thing seems to check the current euid. Am I missing something? > > my (limited) understanding is that you should be using cap checks, not UID > -mike Agreed. This was my initial proposal. It's not very good, but I also think it's the best option for this case. Thanks, -Andrea -- 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/