Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932959AbbDMPvh (ORCPT ); Mon, 13 Apr 2015 11:51:37 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:44745 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932345AbbDMPvf (ORCPT ); Mon, 13 Apr 2015 11:51:35 -0400 Date: Mon, 13 Apr 2015 17:53:31 +0200 From: Quentin Casasnovas To: Quentin Casasnovas Cc: lkml , linux-usb , Phil Turnbull , Oliver Neukum , Adam Lee , Greg Kroah-Hartman Subject: Re: [PATCH] cdc-acm: prevent infinite loop when parsing CDC headers. Message-ID: <20150413155331.GD12442@chrystal.uk.oracle.com> 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> User-Agent: Mutt/1.5.22 (2013-10-16) X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1939 Lines: 53 Adding Greg on CC as suggested by Oliver. 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. > > Fixes: 7e860a6e ("cdc-acm: add sanity checks") > Signed-off-by: Phil Turnbull > Signed-off-by: Quentin Casasnovas > CC: Oliver Neukum > CC: Adam Lee > --- > drivers/usb/class/cdc-acm.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c > index 6836177..1ac4587 100644 > --- a/drivers/usb/class/cdc-acm.c > +++ b/drivers/usb/class/cdc-acm.c > @@ -1133,11 +1133,12 @@ static int acm_probe(struct usb_interface *intf, > } > > while (buflen > 0) { > + if ((elength = buffer[0]) == 0) > + break; > if (buffer[1] != USB_DT_CS_INTERFACE) { > dev_err(&intf->dev, "skipping garbage\n"); > goto next_desc; > } > - elength = buffer[0]; > > switch (buffer[2]) { > case USB_CDC_UNION_TYPE: /* we've found it */ > -- > 2.0.5 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/