From 0687dc06c873d4dac0b604d642d724c2f5abb6b6 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Mon, 19 Apr 2021 15:01:36 -0600
Subject: [PATCH] tun: freebsd: become controlling process when reopening tun
 FD

When we pass the TUN FD to the child, we have to call TUNSIFPID;
otherwise when we close the device, we get a splat in dmesg.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 tun/tun_freebsd.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tun/tun_freebsd.go b/tun/tun_freebsd.go
index 53d4f41..37f1a0c 100644
--- a/tun/tun_freebsd.go
+++ b/tun/tun_freebsd.go
@@ -21,6 +21,7 @@ const (
 	_TUNSIFHEAD = 0x80047460
 	_TUNSIFMODE = 0x8004745e
 	_TUNGIFNAME = 0x4020745d
+	_TUNSIFPID  = 0x2000745f
 
 	_SIOCGIFINFO_IN6        = 0xc048696c
 	_SIOCSIFINFO_IN6        = 0xc048696d
@@ -266,6 +267,15 @@ func CreateTUNFromFile(file *os.File, mtu int) (Device, error) {
 		errors:  make(chan error, 1),
 	}
 
+	var errno syscall.Errno
+	tun.operateOnFd(func(fd uintptr) {
+		_, _, errno = unix.Syscall(unix.SYS_IOCTL, fd, _TUNSIFPID, uintptr(0))
+	})
+	if errno != 0 {
+		tun.tunFile.Close()
+		return nil, fmt.Errorf("unable to become controlling TUN process: %w", errno)
+	}
+
 	name, err := tun.Name()
 	if err != nil {
 		tun.tunFile.Close()