From e7145acd560bd53234abcd0fb11dc381fb900dd3 Mon Sep 17 00:00:00 2001
From: gnattu <gnattu@users.noreply.github.com>
Date: Sat, 25 May 2024 11:46:13 -0400
Subject: [PATCH] Backport pull request #11766 from jellyfin/release-10.9.z

Filter invalid IPs on external interface matching

Original-merge: 2eece01acc32dcd14ea83e224d2bccd8060010e2

Merged-by: crobibero <cody@robibe.ro>

Backported-by: Joshua M. Boniface <joshua@boniface.me>
---
 MediaBrowser.Common/Net/NetworkConstants.cs     |  5 +++++
 .../Manager/NetworkManager.cs                   | 17 ++++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/MediaBrowser.Common/Net/NetworkConstants.cs b/MediaBrowser.Common/Net/NetworkConstants.cs
index b18058fa9..ccef5d271 100644
--- a/MediaBrowser.Common/Net/NetworkConstants.cs
+++ b/MediaBrowser.Common/Net/NetworkConstants.cs
@@ -58,6 +58,11 @@ public static class NetworkConstants
     /// </summary>
     public static readonly IPNetwork IPv4RFC1918PrivateClassC = new IPNetwork(IPAddress.Parse("192.168.0.0"), 16);
 
+    /// <summary>
+    /// IPv4 Link-Local as defined in RFC 3927.
+    /// </summary>
+    public static readonly IPNetwork IPv4RFC3927LinkLocal = new IPNetwork(IPAddress.Parse("169.254.0.0"), 16);
+
     /// <summary>
     /// IPv6 loopback as defined in RFC 4291.
     /// </summary>
diff --git a/src/Jellyfin.Networking/Manager/NetworkManager.cs b/src/Jellyfin.Networking/Manager/NetworkManager.cs
index 70790bb5b..148b33fcb 100644
--- a/src/Jellyfin.Networking/Manager/NetworkManager.cs
+++ b/src/Jellyfin.Networking/Manager/NetworkManager.cs
@@ -903,6 +903,17 @@ public class NetworkManager : INetworkManager, IDisposable
         return false;
     }
 
+    /// <summary>
+    ///  Get if the IPAddress is Link-local.
+    /// </summary>
+    /// <param name="address">The IP Address.</param>
+    /// <returns>Bool indicates if the address is link-local.</returns>
+    public bool IsLinkLocalAddress(IPAddress address)
+    {
+        ArgumentNullException.ThrowIfNull(address);
+        return NetworkConstants.IPv4RFC3927LinkLocal.Contains(address) || address.IsIPv6LinkLocal;
+    }
+
     /// <inheritdoc/>
     public bool IsInLocalNetwork(IPAddress address)
     {
@@ -1084,7 +1095,11 @@ public class NetworkManager : INetworkManager, IDisposable
     private bool MatchesExternalInterface(IPAddress source, out string result)
     {
         // Get the first external interface address that isn't a loopback.
-        var extResult = _interfaces.Where(p => !IsInLocalNetwork(p.Address)).OrderBy(x => x.Index).ToArray();
+        var extResult = _interfaces
+            .Where(p => !IsInLocalNetwork(p.Address))
+            .Where(p => p.Address.AddressFamily.Equals(source.AddressFamily))
+            .Where(p => !IsLinkLocalAddress(p.Address))
+            .OrderBy(x => x.Index).ToArray();
 
         // No external interface found
         if (extResult.Length == 0)