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.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 55b198ba629b..78e92d29f8d9 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -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",