HID: logitech-dj: validate output report details

A HID device could send a malicious output report that would cause the
logitech-dj HID driver to leak kernel memory contents to the device, or
trigger a NULL dereference during initialization:

[  304.424553] usb 1-1: New USB device found, idVendor=046d, idProduct=c52b
...
[  304.780467] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
[  304.781409] IP: [<ffffffff815d50aa>] logi_dj_recv_send_report.isra.11+0x1a/0x90

CVE-2013-2895
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-logitech-dj.c

@@ -461,7 +461,7 @@ static int logi_dj_recv_send_report(struct dj_receiver_dev *djrcv_dev,
 	struct hid_report *report;
 	struct hid_report_enum *output_report_enum;
 	u8 *data = (u8 *)(&dj_report->device_index);
-	int i;
+	unsigned int i;
 
 	output_report_enum = &hdev->report_enum[HID_OUTPUT_REPORT];
 	report = output_report_enum->report_id_hash[REPORT_ID_DJ_SHORT];
@@ -471,7 +471,7 @@ static int logi_dj_recv_send_report(struct dj_receiver_dev *djrcv_dev,
 		return -ENODEV;
 	}
 
-	for (i = 0; i < report->field[0]->report_count; i++)
+	for (i = 0; i < DJREPORT_SHORT_LENGTH - 1; i++)
 		report->field[0]->value[i] = data[i];
 
 	hid_hw_request(hdev, report, HID_REQ_SET_REPORT);
@@ -791,6 +791,12 @@ static int logi_dj_probe(struct hid_device *hdev,
 		goto hid_parse_fail;
 	}
 
+	if (!hid_validate_values(hdev, HID_OUTPUT_REPORT, REPORT_ID_DJ_SHORT,
+				 0, DJREPORT_SHORT_LENGTH - 1)) {
+		retval = -ENODEV;
+		goto hid_parse_fail;
+	}
+
 	/* Starts the usb device and connects to upper interfaces hiddev and
 	 * hidraw */
 	retval = hid_hw_start(hdev, HID_CONNECT_DEFAULT);