Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759352Ab1D0P0K (ORCPT ); Wed, 27 Apr 2011 11:26:10 -0400 Received: from mail-yw0-f46.google.com ([209.85.213.46]:52827 "EHLO mail-yw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755920Ab1D0P0I convert rfc822-to-8bit (ORCPT ); Wed, 27 Apr 2011 11:26:08 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type :content-transfer-encoding; b=DwKRDcRPgIOktD93SY/E/1Datfy9L6YlxrWL3wwp8OKDfZJ816skY3WTZSGuD7U8jX uIzcU2dszzdv1dCxn7NEk3/klWbLHzu2n+A0HFbvuUtPCAoUaZnIjyPzBp4B4sp1pdKg NrBAppleQA11XHoRNmsw3Y+B7I7Fbh88NWk3E= MIME-Version: 1.0 In-Reply-To: <20110427095709.GA1687@linux.develer.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> From: Mike Frysinger Date: Wed, 27 Apr 2011 11:25:47 -0400 X-Google-Sender-Auth: IdJkocejDIna4yBhp2MtiFlLxIs Message-ID: Subject: Re: [RFC] [PATCH] drop_pagecache syscall To: Andrea Righi Cc: Andrea Righi , Dave Chinner , Andrew Morton , Al Viro , Arnd Bergmann , linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2395 Lines: 46 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 -- 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/