linux-kernel - Re: usb/core: slab-out-of-bounds in usb_get_bos

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Message-ID: <Pine.LNX.4.44L0.1710181124310.1528-100000@iolanthe.rowland.org>
Date:   Wed, 18 Oct 2017 11:25:20 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Andrey Konovalov <andreyknvl@...gle.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        Dmitry Fleytman <dmitry@...nix.com>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: usb/core: slab-out-of-bounds in usb_get_bos_descriptor

On Wed, 18 Oct 2017, Andrey Konovalov wrote:

> Hi!
> 
> I've got the following report while fuzzing the kernel with syzkaller.
> 
> On commit 3e0cc09a3a2c40ec1ffb6b4e12da86e98feccb11 (4.14-rc5+).
> 
> Looks like usb_get_bos_descriptor() doesn't check that buffer has
> enough space for usb_dev_cap_header, which causes out-of-bounds
> accesses.

Please try the patch below.

Alan Stern



Index: usb-4.x/drivers/usb/core/config.c
===================================================================
--- usb-4.x.orig/drivers/usb/core/config.c
+++ usb-4.x/drivers/usb/core/config.c
@@ -952,10 +952,12 @@ int usb_get_bos_descriptor(struct usb_de
 	for (i = 0; i < num; i++) {
 		buffer += length;
 		cap = (struct usb_dev_cap_header *)buffer;
-		length = cap->bLength;
 
-		if (total_len < length)
+		if (total_len < sizeof(*cap) || total_len < cap->bLength) {
+			dev->bos->desc->bNumDeviceCaps = i;
 			break;
+		}
+		length = cap->bLength;
 		total_len -= length;
 
 		if (cap->bDescriptorType != USB_DT_DEVICE_CAPABILITY) {