linux-kernel - Re: usb/hid: slab-out-of-bounds read in usbhid

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Message-ID: <CAL6iAa+1MYuu6rvuUY2f7tH+SeBu-0PPeRQN9fJXW6uzj_f2+g@mail.gmail.com>
Date:   Thu, 21 Sep 2017 10:42:12 +0900
From:   Jaejoong Kim <climbbb.kim@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        USB list <linux-usb@...r.kernel.org>,
        linux-input@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>
Subject: Re: usb/hid: slab-out-of-bounds read in usbhid_parse

Hi Alan

2017-09-21 0:50 GMT+09:00 Alan Stern <stern@...land.harvard.edu>:
> On Wed, 20 Sep 2017, Kim Jaejoong wrote:
>
>> To. usb & input guys.
>>
>> While dig this report, i was wondering about bNumDescriptors in HID descriptor.
>> HID document from usb.org said, 'this number must be at least one (1)
>> as a Report descriptor will always be present.'
>>
>> There is no mention of the order of class descriptors. Suppose you
>> have a HID device with a report descriptor and a physical descriptor.
>>
>> If you have the following hid descriptor in this case,
>> HID descriptor
>>    bLength: 12
>>    bDescriptor Type: HID
>>    .. skip
>>    bNumDescriptors: 2
>>    bDescriptorType: physical
>>    bDescriptorLength: any
>>    bDescriptorType: Report
>>    bDescriptorLength: any
>>
>> If the order of the report descriptor is the second as above,
>> usbhid_parse () will fail because my patch is only check the first
>> bDescriptor Type.
>> But If the order of the report descriptor is always first, there is no
>> problem. How do you think this?
>
> The descriptors can appear in any order.  You should not assume that
> the report descriptor will always come first.

Thanks for clarifying. I will resend patch with modification.

Jaejoong

>
> Alan Stern
>