From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751997AbWG1PFz (ORCPT ); Fri, 28 Jul 2006 11:05:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752009AbWG1PFz (ORCPT ); Fri, 28 Jul 2006 11:05:55 -0400 Received: from ms-smtp-03.nyroc.rr.com ([24.24.2.57]:31921 "EHLO ms-smtp-03.nyroc.rr.com") by vger.kernel.org with ESMTP id S1751997AbWG1PFy (ORCPT ); Fri, 28 Jul 2006 11:05:54 -0400 Subject: Re: A better interface, perhaps: a timed signal flag From: Steven Rostedt To: Theodore Tso Cc: Neil Horman , "H. Peter Anvin" , Segher Boessenkool , Dave Airlie , linux-kernel@vger.kernel.org, a.zummo@towertech.it, jg@freedesktop.org In-Reply-To: <20060728145210.GA3566@thunk.org> References: <44C67E1A.7050105@zytor.com> <20060725204736.GK4608@hmsreliant.homelinux.net> <44C6842C.8020501@zytor.com> <20060725222547.GA3973@localhost.localdomain> <70FED39F-E2DF-48C8-B401-97F8813B988E@kernel.crashing.org> <20060725235644.GA5147@localhost.localdomain> <44C6B117.80300@zytor.com> <20060726002043.GA5192@localhost.localdomain> <20060726144536.GA28597@thunk.org> <1154093606.19722.11.camel@localhost.localdomain> <20060728145210.GA3566@thunk.org> Content-Type: text/plain Date: Fri, 28 Jul 2006 11:05:16 -0400 Message-Id: <1154099116.19722.15.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2006-07-28 at 10:52 -0400, Theodore Tso wrote: > Good point, and limiting this facility to one such timeout per > task_struct seems like a reasonable restriction. The downsides I can > see about about mapping the tasks' own task struct would be (a) a > potential security leak either now or in the future if some field in > the task_struct shouldn't be visible to a non-privileged userspace > program, and (b) exposing the task_struct might cause some (stupid) > programs to depend on the task_struct layout. Allocating an otherwise > empty 4k page just for this purpose wouldn't be all that horrible, > though, and would avoid these potential problems. Actually, if you are going to map a page, then allow the user to do PAGE_SIZE / sizeof(*flag) timers. That way the user gets a single page mapped for this purpose, and can have multiple flags. I would only limit it to one page though. Since this page can not be swapped out, if you allow for more than one page, a non privileged user can map in a bunch of non swappable pages and might be able to perform a DoS attack. -- Steve