linux-kernel - [PATCH 4.9 008/177] USB: core: prevent malicious bNumInterfaces overflow

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Message-Id: <20171218152910.269130546@linuxfoundation.org>
Date:   Mon, 18 Dec 2017 16:47:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alan Stern <stern@...land.harvard.edu>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH 4.9 008/177] USB: core: prevent malicious bNumInterfaces overflow

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alan Stern <stern@...land.harvard.edu>

commit 48a4ff1c7bb5a32d2e396b03132d20d552c0eca7 upstream.

A malicious USB device with crafted descriptors can cause the kernel
to access unallocated memory by setting the bNumInterfaces value too
high in a configuration descriptor.  Although the value is adjusted
during parsing, this adjustment is skipped in one of the error return
paths.

This patch prevents the problem by setting bNumInterfaces to 0
initially.  The existing code already sets it to the proper value
after parsing is complete.

Signed-off-by: Alan Stern <stern@...land.harvard.edu>
Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/core/config.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -550,6 +550,9 @@ static int usb_parse_configuration(struc
 	unsigned iad_num = 0;
 
 	memcpy(&config->desc, buffer, USB_DT_CONFIG_SIZE);
+	nintf = nintf_orig = config->desc.bNumInterfaces;
+	config->desc.bNumInterfaces = 0;	// Adjusted later
+
 	if (config->desc.bDescriptorType != USB_DT_CONFIG ||
 	    config->desc.bLength < USB_DT_CONFIG_SIZE ||
 	    config->desc.bLength > size) {
@@ -563,7 +566,6 @@ static int usb_parse_configuration(struc
 	buffer += config->desc.bLength;
 	size -= config->desc.bLength;
 
-	nintf = nintf_orig = config->desc.bNumInterfaces;
 	if (nintf > USB_MAXINTERFACES) {
 		dev_warn(ddev, "config %d has too many interfaces: %d, "
 		    "using maximum allowed: %d\n",