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From 4c5ae6a301a5415d1334f6c655bebf91d475bd89 Mon Sep 17 00:00:00 2001
From: Alan Stern <stern@rowland.harvard.edu>
Date: Tue, 12 Dec 2017 14:25:13 -0500
Subject: [PATCH] USB: core: prevent malicious bNumInterfaces overflow
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.
CVE: CVE-2017-17558
Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=4c5ae6a301a5415d1334f6c655bebf91d475bd89]
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>
Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>
---
drivers/usb/core/config.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index c42a3e63eb07..843ef46d2537 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",
--
2.20.1
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