staging: ks7010: prevent buffer overflow in ks_wlan_set_scan()

commit e163b98 upstream.

The user can specify a "req->essid_len" of up to 255 but if it's
over IW_ESSID_MAX_SIZE (32) that can lead to memory corruption.

Fixes: 13a9930 ("staging: ks7010: add driver from Nanonote extra-repository")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/YD4fS8+HmM/Qmrw6@mwanda
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/ks7010/ks_wlan_net.c

@@ -1120,6 +1120,7 @@ static int ks_wlan_set_scan(struct net_device *dev,
 {
 	struct ks_wlan_private *priv = netdev_priv(dev);
 	struct iw_scan_req *req = NULL;
+	int len;
 
 	if (priv->sleep_mode == SLP_SLEEP)
 		return -EPERM;
@@ -1129,8 +1130,9 @@ static int ks_wlan_set_scan(struct net_device *dev,
 	if (wrqu->data.length == sizeof(struct iw_scan_req) &&
 	    wrqu->data.flags & IW_SCAN_THIS_ESSID) {
 		req = (struct iw_scan_req *)extra;
-		priv->scan_ssid_len = req->essid_len;
-		memcpy(priv->scan_ssid, req->essid, priv->scan_ssid_len);
+		len = min_t(int, req->essid_len, IW_ESSID_MAX_SIZE);
+		priv->scan_ssid_len = len;
+		memcpy(priv->scan_ssid, req->essid, len);
 	} else {
 		priv->scan_ssid_len = 0;
 	}