From 7f5ad3e503f231893dc5d298f703c4b72b83bdb9 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Wed, 16 Jun 2021 15:56:21 +0200
Subject: [PATCH] Kit: Adapter: iterate through all FDs to find UTUN

This is a bit of a kludge, until I find something better. We simply
iterate through all FDs, and call getsockopt on each one until we find
the utun FD. This works, and completes rather quickly (fd is usually 6
or 7). Rather than maintain the old path for older kernels, just use
this for all versions, to get more coverage. Other techniques involve
undocumented APIs; this one has the advantage of using nothing
undocumented.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 Sources/WireGuardKit/WireGuardAdapter.swift | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/Sources/WireGuardKit/WireGuardAdapter.swift b/Sources/WireGuardKit/WireGuardAdapter.swift
index 0ed9b3b..b18769e 100644
--- a/Sources/WireGuardKit/WireGuardAdapter.swift
+++ b/Sources/WireGuardKit/WireGuardAdapter.swift
@@ -57,7 +57,14 @@ public class WireGuardAdapter {
 
     /// Tunnel device file descriptor.
     private var tunnelFileDescriptor: Int32? {
-        return self.packetTunnelProvider?.packetFlow.value(forKeyPath: "socket.fileDescriptor") as? Int32
+        var buf = [CChar](repeating: 0, count: Int(IFNAMSIZ))
+        for fd: Int32 in 0...1024 {
+            var len = socklen_t(buf.count)
+            if getsockopt(fd, SYSPROTO_CONTROL, 2, &buf, &len) == 0 && String(cString: buf).hasPrefix("utun") {
+                return fd
+            }
+        }
+        return nil
     }
 
     /// Returns a WireGuard version.