HID: ntrig: validate feature report details

A HID device could send a malicious feature report that would cause the
ntrig HID driver to trigger a NULL dereference during initialization:

[57383.031190] usb 3-1: New USB device found, idVendor=1b96, idProduct=0001
...
[57383.315193] BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
[57383.315308] IP: [<ffffffffa08102de>] ntrig_probe+0x25e/0x420 [hid_ntrig]

CVE-2013-2896

Signed-off-by: Kees Cook <[e-mail]>
Cc: [e-mail]
Signed-off-by: Rafi Rubin <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

drivers/hid/hid-ntrig.c

···
 	struct hid_report *report = hdev->report_enum[HID_FEATURE_REPORT].
 				    report_id_hash[0x0d];
 
-	if (!report)
+	if (!report || report->maxfield < 1 ||
+	    report->field[0]->report_count < 1)
 		return -EINVAL;
 
 	hid_hw_request(hdev, report, HID_REQ_GET_REPORT);