On Thu, Aug 29, 2013 at 4:40 PM, Kees Cook <[email protected]> wrote:
> On Thu, Aug 29, 2013 at 2:48 AM, Benjamin Tissoires
> <[email protected]> wrote:
>> On Wed, Aug 28, 2013 at 10:30 PM, Jiri Kosina <[email protected]> wrote:
>>> From: Kees Cook <[email protected]>
>>>
>>> This driver must validate the availability of the HID output report and
>>> its size before it can write LED states via buzz_set_leds(). This stops
>>> a heap overflow that is possible if a device provides a malicious HID
>>> output report:
>>>
>>> [ 108.171280] usb 1-1: New USB device found, idVendor=054c, idProduct=0002
>>> ...
>>> [ 117.507877] BUG kmalloc-192 (Not tainted): Redzone overwritten
>>>
>>> CVE-2013-2890
>>>
>>> Signed-off-by: Kees Cook <[email protected]>
>>> Cc: [email protected]
>>> ---
>>> drivers/hid/hid-sony.c | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/hid/hid-sony.c b/drivers/hid/hid-sony.c
>>> index 87fbe29..b987926 100644
>>> --- a/drivers/hid/hid-sony.c
>>> +++ b/drivers/hid/hid-sony.c
>>> @@ -537,6 +537,10 @@ static int buzz_init(struct hid_device *hdev)
>>> drv_data = hid_get_drvdata(hdev);
>>> BUG_ON(!(drv_data->quirks & BUZZ_CONTROLLER));
>>>
>>> + /* Validate expected report characteristics. */
>>> + if (!hid_validate_report(hdev, HID_OUTPUT_REPORT, 0, 1, 7))
>>
>> I don't have access to the device anymore, but I still kept the report
>> descriptors (this is the interesting part):
>>
>> 0xa1, 0x02, // Collection (Logical) 60
>> 0x75, 0x08, // Report Size (8) 62
>> 0x95, 0x07, // Report Count (7) 64
>> 0x46, 0xff, 0x00, // Physical Maximum (255) 66
>> 0x26, 0xff, 0x00, // Logical Maximum (255) 69
>> 0x09, 0x02, // Usage (Vendor Usage 2) 72
>> 0x91, 0x02, // Output (Data,Var,Abs) 74
>> 0xc0, // End Collection 76
>>
>> So with the current implementation of hid_validate_report(), it works,
>> but if another Buzz controller show up at some point with extras
>> fields in this output report... we will be screwed. So please, amend
>> hid_validate_report(), or specifically test here that the LED output
>> report is 7 bytes.
>
> hid_validate_report() checks for "at least" 7 in this call, so it
> should be fine, unless I've misunderstood something.
>
Sure, it' s fine with the current implementation of
hid_validate_report(). However, as I mentioned in patch
2/14, I am complaining about the implementation of hid_validate_report().
In this case, if a new Buzz controller pops out with an extra usage
(Vendor 3 for instance), mapped to another LED, and that the report
count is for this usage < 7, the test invalidate the report.
for instance, let's imagine they pop up a new version:
0xa1, 0x02, // Collection (Logical) 60
0x75, 0x08, // Report Size (8) 62
0x95, 0x07, // **Report Count (7)** 64
0x46, 0xff, 0x00, // Physical Maximum (255) 66
0x26, 0xff, 0x00, // Logical Maximum (255) 69
0x09, 0x02, // Usage (Vendor Usage 2) 72
0x91, 0x02, // Output (Data,Var,Abs) 74
0x75, 0x08, // Report Size (8) 62
0x95, 0x04, // **Report Count (4)** 64
0x46, 0xff, 0x00, // Physical Maximum (255) 66
0x26, 0xff, 0x00, // Logical Maximum (255) 69
0x09, 0x03, // Usage (Vendor Usage 3) 72
0x91, 0x02, // Output (Data,Var,Abs) 74
0xc0, // End Collection 76
Ok, it's a lot of "if", but still this output report is valid, and the
test will fail. And if we call hid_validate_report(hdev,
HID_OUTPUT_REPORT, 0, 1, 4), the validation will fail, but the heap
overflow will appear again.
Does it makes more sense?
Cheers,
Benjamin
>>> + return -ENODEV;
>>> +
>>> buzz = kzalloc(sizeof(*buzz), GFP_KERNEL);
>>> if (!buzz) {
>>> hid_err(hdev, "Insufficient memory, cannot allocate driver
>>> data\n");
>>>
>>> --
>>> Jiri Kosina
>>> SUSE Labs
>>> --
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>
>
>
> --
> Kees Cook
> Chrome OS Security
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