Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754210AbbDNJXu (ORCPT ); Tue, 14 Apr 2015 05:23:50 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:18671 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752294AbbDNJXj (ORCPT ); Tue, 14 Apr 2015 05:23:39 -0400 From: Quentin Casasnovas To: lkml Cc: linux-usb , Adam Lee , Greg Kroah-Hartman , Sergei Shtylyov , Oliver Neukum , Phil Turnbull , Quentin Casasnovas Subject: [PATCH v2] cdc-acm: prevent infinite loop when parsing CDC headers. Date: Tue, 14 Apr 2015 11:25:43 +0200 Message-Id: <1429003543-15856-1-git-send-email-quentin.casasnovas@oracle.com> X-Mailer: git-send-email 2.0.5 In-Reply-To: <1428938644-19942-1-git-send-email-quentin.casasnovas@oracle.com> References: <1428938644-19942-1-git-send-email-quentin.casasnovas@oracle.com> X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2109 Lines: 62 Phil and I found out a problem with commit: 7e860a6e7aa6 ("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. v2: - Use 12-digits sha1 to reference the offending commit. - Do not break from the loop and try next byte instead. - Move the assignment outside the 'if'. - Add a debug print. Fixes: 7e860a6e7aa6 ("cdc-acm: add sanity checks") Signed-off-by: Phil Turnbull Signed-off-by: Quentin Casasnovas CC: Sergei Shtylyov CC: Oliver Neukum CC: Adam Lee CC: --- drivers/usb/class/cdc-acm.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 6836177..220c0fd 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -1133,11 +1133,16 @@ static int acm_probe(struct usb_interface *intf, } while (buflen > 0) { + elength = buffer[0]; + if (!elength) { + dev_err(&intf->dev, "skipping garbage byte\n"); + elength = 1; + goto next_desc; + } 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/