staging/cxt1e1/linux.c: Correct arbitrary memory write in c4_ioctl()

The function c4_ioctl() writes data from user in ifr->ifr_data
to the kernel struct data arg, without any iolen bounds checking.
This can lead to a arbitrary write outside of the struct data arg.
Corrected by adding bounds-checking of iolen before the copy_from_user().
Signed-off-by: Salva Peiró <speiro@ai2.upv.es>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/cxt1e1/linux.c

@@ -866,6 +866,8 @@ c4_ioctl (struct net_device *ndev, struct ifreq *ifr, int cmd)
             _IOC_SIZE (iocmd));
 #endif
     iolen = _IOC_SIZE (iocmd);
+    if (iolen > sizeof(arg))
+        return -EFAULT;
     data = ifr->ifr_data + sizeof (iocmd);
     if (copy_from_user (&arg, data, iolen))
         return -EFAULT;