From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934705Ab2C3Ump (ORCPT ); Fri, 30 Mar 2012 16:42:45 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:48002 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934656Ab2C3Umk (ORCPT ); Fri, 30 Mar 2012 16:42:40 -0400 Date: Fri, 30 Mar 2012 13:42:35 -0700 From: Greg KH To: Thomas Gleixner Cc: Sasha Levin , arnd@arndb.de, viro@zeniv.linux.org.uk, davej@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] kmsg: Use vmalloc instead of kmalloc when writing Message-ID: <20120330204235.GA883@kroah.com> References: <1333127067-2043-1-git-send-email-levinsasha928@gmail.com> <20120330153013.GC18488@kroah.com> <20120330164913.GA19946@kroah.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/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 30, 2012 at 10:35:46PM +0200, Thomas Gleixner wrote: > On Fri, 30 Mar 2012, Greg KH wrote: > > On Fri, Mar 30, 2012 at 07:37:37PM +0300, Sasha Levin wrote: > > > On Fri, Mar 30, 2012 at 6:30 PM, Greg KH wrote: > > > > On Fri, Mar 30, 2012 at 01:04:27PM -0400, Sasha Levin wrote: > > > >> There are no size checks in kmsg_write(), and we try allocating enough > > > >> memory to store everything userspace gave us, which may be too much for > > > >> kmalloc to allocate. > > > > > > > > Really?  Have you seen this fail?  As only root can do this, is this > > > > really a problem? > > > > > > Only root, and a whole bunch of management software that dumps data > > > into /dev/kmsg (systemd and friends). > > > > Running as root, do any of these cause problems by asking for too much > > memory here? > > Running as root is not a guarantee for correctness. So the syscall > should cope with bogus requests from user space and not rely on the > sanity of anything. Looking at the main users which polute dmesg I'm > inclined to assume insanity in the first place. > > As Sasha pointed out there is either the variant to use vmalloc and > grant any write size or limit the size to something sensible. Though > given the users of this, coming up with something sensible might be a > problem. > > > Is this something that needs to be addressed now, and in > > stable kernels, or can it wait for 3.5? > > Yes, it want's to be addressed now and it want's to be in stable as > well. syscalls which have no bound checking are evil, no matter what. So, should we cap the size at something "super large" then as well? thanks, greg k-h