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USB: core: prevent malicious bNumInterfaces overflow

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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@rowland.harvard.edu>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alan Stern 2017-12-12 14:25:13 -05:00 committed by Greg Kroah-Hartman
parent 05de6fa5c0
commit dfdf5fa3e6
1 changed files with 3 additions and 1 deletions
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4
drivers/usb/core/config.c
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@ -521,6 +521,9 @@ 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) {
@ -534,7 +537,6 @@ 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",