HID: steam: Prevent NULL pointer dereference in steam_{recv,send}_report

It is possible for a malicious device to forgo submitting a Feature
Report.  The HID Steam driver presently makes no prevision for this
and de-references the 'struct hid_report' pointer obtained from the
HID devices without first checking its validity.  Let's change that.

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: linux-input@vger.kernel.org
Fixes: c164d6abf3 ("HID: add driver for Valve Steam Controller")
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-steam.c

@@ -134,6 +134,11 @@ static int steam_recv_report(struct steam_device *steam,
 	int ret;
 
 	r = steam->hdev->report_enum[HID_FEATURE_REPORT].report_id_hash[0];
+	if (!r) {
+		hid_err(steam->hdev, "No HID_FEATURE_REPORT submitted -  nothing to read\n");
+		return -EINVAL;
+	}
+
 	if (hid_report_len(r) < 64)
 		return -EINVAL;
 
@@ -165,6 +170,11 @@ static int steam_send_report(struct steam_device *steam,
 	int ret;
 
 	r = steam->hdev->report_enum[HID_FEATURE_REPORT].report_id_hash[0];
+	if (!r) {
+		hid_err(steam->hdev, "No HID_FEATURE_REPORT submitted -  nothing to read\n");
+		return -EINVAL;
+	}
+
 	if (hid_report_len(r) < 64)
 		return -EINVAL;