tun: Get skfilter layout

The only thing we may have from tun device is the fprog, whic contains
the number of filter elements and a pointer to (user-space) memory
where the elements are. The program itself may not be available if the
device is persistent and detached.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -2042,6 +2042,16 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		tun_detach_filter(tun, tun->numqueues);
 		break;
 
+	case TUNGETFILTER:
+		ret = -EINVAL;
+		if ((tun->flags & TUN_TYPE_MASK) != TUN_TAP_DEV)
+			break;
+		ret = -EFAULT;
+		if (copy_to_user(argp, &tun->fprog, sizeof(tun->fprog)))
+			break;
+		ret = 0;
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;

include/uapi/linux/if_tun.h

@@ -57,6 +57,7 @@
 #define TUNSETVNETHDRSZ _IOW('T', 216, int)
 #define TUNSETQUEUE  _IOW('T', 217, int)
 #define TUNSETIFINDEX	_IOW('T', 218, unsigned int)
+#define TUNGETFILTER _IOR('T', 219, struct sock_fprog)
 
 /* TUNSETIFF ifr flags */
 #define IFF_TUN		0x0001