On Thu, Aug 29, 2013 at 9:58 PM, Kees Cook [off-list ref] wrote:

On Thu, Aug 29, 2013 at 7:50 AM, Benjamin Tissoires
[off-list ref] wrote:

quoted

On Thu, Aug 29, 2013 at 4:40 PM, Kees Cook [off-list ref] wrote:

quoted

On Thu, Aug 29, 2013 at 2:48 AM, Benjamin Tissoires
[off-list ref] wrote:

quoted

On Wed, Aug 28, 2013 at 10:30 PM, Jiri Kosina [off-list ref] wrote:

quoted

From: Kees Cook <redacted>

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 <redacted>
Cc: stable@kernel.org
---
 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?

Right, yeah, I understand what you meant here, but I guess my point
was, if there's something that uses <7, then the driver needs
adjustment too, beyond just the hid_validate_report() call, since it
would need to know to operate only on 4 instead of 7. My thinking was,
if such a thing is detected, it would need to identify which device it
was and fix both the bounds-checking, and the report-value-setting.
For example:

if (i_am_vendor_3()) {
  hid_validate_report(hdev, HID_OUTPUT_REPORT, 0, 1, 4);
} else {
  hid_validate_report(hdev, HID_OUTPUT_REPORT, 0, 1, 7);
}

hmm... not really. In my case, I supposed the device presented both vendor collections, one after the other. So the test could be:

hid_validate_report(hdev, HID_OUTPUT_REPORT, 0, 1, 7);
if (I_contain_vendor_3())
    hid_validate_report(hdev, HID_OUTPUT_REPORT, 0, 2, 4);

But this will not work if the small report is in front of the large one.

I can propose another implementation of hid_validate_report() which will be covering this case:
instead of checking a range of fields, just check the specific field index used later:

+struct hid_report *hid_validate_report(struct hid_device *hid,
+				       unsigned int type, unsigned int id,
+				       unsigned int field_index,
+				       unsigned int report_counts)
+{
+	struct hid_report *report;
+
+	if (type > HID_FEATURE_REPORT) {
+		hid_err(hid, "invalid HID report %u\n", type);
+		return NULL;
+	}
+
+	report = hid->report_enum[type].report_id_hash[id];
+	if (!report) {
+		hid_err(hid, "missing %s %u\n", hid_report_names[type], id);
+		return NULL;
+	}
+	if (report->maxfield <= field_index) {
+		hid_err(hid, "not enough fields in %s %u\n",
+			hid_report_names[type], id);
+		return NULL;
+	}
+	
+	if (report->field[field_index]->report_count < report_counts) {
+		hid_err(hid, "not enough values in %s %u field #%d\n",
+				hid_report_names[type], id, field_index);
+			return NULL;
+	}
+	return report;
+}
+EXPORT_SYMBOL_GPL(hid_validate_report);

Only hid-zpff and hid-lenovo-tpkbd are checking for more than one report, and we can afford a for loop on the field indexes for them.

Cheers,
Benjamin

...

        value[0] = 0x00;
        value[1] = (leds & 1) ? 0xff : 0x00;
        value[2] = (leds & 2) ? 0xff : 0x00;
        value[3] = (leds & 4) ? 0xff : 0x00;
        if (!i_am_vendor_3()) {
            value[4] = (leds & 8) ? 0xff : 0x00;
            value[5] = 0x00;
            value[6] = 0x00;
         }

But actually, the logic would be id or usage based, but still, it
seems to me that the hid_validate_report() call must match the actual
value array assignments.

-Kees

quoted

Cheers,
Benjamin

quoted

quoted

quoted

+               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

--
Kees Cook
Chrome OS Security