From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752062AbaESWZM (ORCPT ); Mon, 19 May 2014 18:25:12 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:49930 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750894AbaESWZL (ORCPT ); Mon, 19 May 2014 18:25:11 -0400 Date: Mon, 19 May 2014 15:25:00 -0700 From: Greg Kroah-Hartman To: Tejun Heo Cc: linux-kernel@vger.kernel.org, Kay Sievers , Ron , Ben Hutchings Subject: Re: [PATCH driver-core-linus] sysfs: make sure read buffer is zeroed Message-ID: <20140519222500.GA14616@kroah.com> References: <20140519172334.GK20439@audi.shelbyville.oz> <20140519195210.GA27506@mtj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140519195210.GA27506@mtj.dyndns.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 19, 2014 at 03:52:10PM -0400, Tejun Heo wrote: > 13c589d5b0ac ("sysfs: use seq_file when reading regular files") > switched sysfs from custom read implementation to seq_file to enable > later transition to kernfs. After the change, the buffer passed to > ->show() is acquired through seq_get_buf(); unfortunately, this > introduces a subtle behavior change. Before the commit, the buffer > passed to ->show() was always zero as it was allocated using > get_zeroed_page(). Because seq_file doesn't clear buffers on > allocation and neither does seq_get_buf(), after the commit, depending > on the behavior of ->show(), we may end up exposing uninitialized data > to userland thus possibly altering userland visible behavior and > leaking information. > > Fix it by explicitly clearing the buffer. > > Signed-off-by: Tejun Heo > Reported-by: Ron > Fixes: 13c589d5b0ac ("sysfs: use seq_file when reading regular files") > --- > fs/sysfs/file.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c > index 28cc1acd..e9ef59b 100644 > --- a/fs/sysfs/file.c > +++ b/fs/sysfs/file.c > @@ -47,12 +47,13 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v) > ssize_t count; > char *buf; > > - /* acquire buffer and ensure that it's >= PAGE_SIZE */ > + /* acquire buffer and ensure that it's >= PAGE_SIZE and clear */ > count = seq_get_buf(sf, &buf); > if (count < PAGE_SIZE) { > seq_commit(sf, -1); > return 0; > } > + memset(buf, 0, PAGE_SIZE); > > /* > * Invoke show(). Control may reach here via seq file lseek even Thanks, I'll go queue this up. greg k-h