From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932471AbbDMPsm (ORCPT ); Mon, 13 Apr 2015 11:48:42 -0400 Received: from mail-pa0-f48.google.com ([209.85.220.48]:34435 "EHLO mail-pa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754110AbbDMPsh (ORCPT ); Mon, 13 Apr 2015 11:48:37 -0400 Date: Mon, 13 Apr 2015 23:48:27 +0800 From: Adam Lee To: Quentin Casasnovas Cc: lkml , linux-usb , Phil Turnbull , Oliver Neukum Subject: Re: [PATCH] cdc-acm: prevent infinite loop when parsing CDC headers. Message-ID: <20150413154827.GA2458@adam-laptop> References: <1428938644-19942-1-git-send-email-quentin.casasnovas@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1428938644-19942-1-git-send-email-quentin.casasnovas@oracle.com> X-PGP-Key-ID: 2F39D84D 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, Apr 13, 2015 at 05:24:04PM +0200, Quentin Casasnovas wrote: > Phil and I found out a problem with commit: > > 7e860a6e ("cdc-acm: add sanity checks") > > It added some sanity checks to ignore potential garbage in CDC headers but > also introduced a potential infinite loop. This can happen at the first > loop iteration (elength = 0 in that case) if the description isn't a > DT_CS_INTERFACE or later if 'buffer[0]' is zero. > > It should also be noted that the wrong length was being added to 'buffer' > in case 'buffer[1]' was not a DT_CS_INTERFACE descriptor, since elength was > assigned after that check in the loop. > > A specially crafted USB device could be used to trigger this infinite loop. Yes, "elength = buffer[0]" should be moved to the front of USB_DT_CS_INTERFACE check, ACK this part. But I don't know in what case the buffer[0] could be zero, if it happens, better to set elength 1 then goto next_desc? (I'm not a maintainer, pleas also consider others' opinion) -- Adam Lee http://adam8157.info