staging: rtl8192u: fix ->ssid overflow in r8192_wx_set_scan()

We need to cap len at IW_ESSID_MAX_SIZE (32) to avoid memory corruption.
This can be controlled by the user via the ioctl.

Fixes: 5f53d8c ("Staging: add rtl8192SU wireless usb driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/YEHoAWMOSZBUw91F@mwanda
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Dan Carpenter

drivers/staging/rtl8192u/r8192U_wx.c

@@ -331,8 +331,10 @@ static int r8192_wx_set_scan(struct net_device *dev, struct iw_request_info *a,
 		struct iw_scan_req *req = (struct iw_scan_req *)b;
 
 		if (req->essid_len) {
-			ieee->current_network.ssid_len = req->essid_len;
-			memcpy(ieee->current_network.ssid, req->essid, req->essid_len);
+			int len = min_t(int, req->essid_len, IW_ESSID_MAX_SIZE);
+
+			ieee->current_network.ssid_len = len;
+			memcpy(ieee->current_network.ssid, req->essid, len);
 		}
 	}