From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755284Ab3AYDvH (ORCPT ); Thu, 24 Jan 2013 22:51:07 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34195 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754372Ab3AYDvE (ORCPT ); Thu, 24 Jan 2013 22:51:04 -0500 Message-ID: <51020120.5000500@redhat.com> Date: Fri, 25 Jan 2013 11:50:56 +0800 From: Lingzhu Xiang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Al Viro CC: Matt Fleming , linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] efivars write(2) races References: <20130125002552.GC4503@ZenIV.linux.org.uk> In-Reply-To: <20130125002552.GC4503@ZenIV.linux.org.uk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/25/2013 08:25 AM, Al Viro wrote: > 1) process A does write() on efivars file, reaches ->get_variable(), > gets newdatasize set, drops efivars->lock and loses CPU before an attempt to > grab ->i_mutex. process B comes and does the same thing, replacing the > variable contents. Then it grabs ->i_mutex, updates size, drops ->i_mutex > and buggers off. At which point A gets CPU back and proceeds to set size > to whatever would be valid for its write. Only the value is bogus now... There are a few other things that makes size bogus now. 1. truncate() never touches nvram but pretends to be changing size. 2. Empty files come back with non-zero size after remount. They are imported from sysfs when mounting. 3. Arguably reading empty files could just return empty instead of returning EIO/EFI_NOT_FOUND from firmware. 4. EFI_VARIABLE_APPEND_WRITE with EFI_OUT_OF_RESOURCES truncates size but you can still read its content.