patch "USB: core: prevent malicious bNumInterfaces overflow" added to usb-linus

This is a note to let you know that I've just added the patch titled

USB: core: prevent malicious bNumInterfaces overflow

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Alan Stern <[email protected]>
Date: Tue, 12 Dec 2017 14:25:13 -0500
Subject: USB: core: prevent malicious bNumInterfaces overflow

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.

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

index 55b198ba629b..78e92d29f8d9 100644
@@ -555,6 +555,9 @@ static int usb_parse_configuration(struct usb_device *dev, int cfgidx,
 	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) {

@@ -568,7 +571,6 @@ static int usb_parse_configuration(struct usb_device *dev, int cfgidx,
 	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",

2.15.1