fix(android): Handle case where connlibSessionPtr can be null in NetworkMonitor (#5496)

Connlib session pointer can be null if the service was shutdown before
the NetworkMonitor has stopped, causing a race condition.

Fixes #4758

kotlin/android/app/src/main/java/dev/firezone/android/tunnel/NetworkMonitor.kt

@@ -18,20 +18,28 @@ class NetworkMonitor(private val tunnelService: TunnelService) : ConnectivityMan
         linkProperties: LinkProperties,
     ) {
         Log.d("NetworkMonitor", "OnLinkPropertiesChanged: $network: $linkProperties")
-        if (tunnelService.tunnelState != TunnelService.Companion.State.UP) {
-            tunnelService.tunnelState = TunnelService.Companion.State.UP
-            tunnelService.updateStatusNotification(TunnelStatusNotification.Connected)
+
+        // Acquire mutex lock
+        if (tunnelService.lock.tryLock()) {
+            if (tunnelService.tunnelState != TunnelService.Companion.State.UP) {
+                tunnelService.tunnelState = TunnelService.Companion.State.UP
+                tunnelService.updateStatusNotification(TunnelStatusNotification.Connected)
+            }
+
+            if (lastDns != linkProperties.dnsServers) {
+                lastDns = linkProperties.dnsServers
+                ConnlibSession.setDns(tunnelService.connlibSessionPtr!!, Gson().toJson(linkProperties.dnsServers))
+            }
+
+            if (lastNetwork != network) {
+                lastNetwork = network
+                ConnlibSession.reconnect(tunnelService.connlibSessionPtr!!)
+            }
+
+            // Release mutex lock
+            tunnelService.lock.unlock()
         }
 
-        if (lastDns != linkProperties.dnsServers) {
-            lastDns = linkProperties.dnsServers
-            ConnlibSession.setDns(tunnelService.connlibSessionPtr!!, Gson().toJson(linkProperties.dnsServers))
-        }
-
-        if (lastNetwork != network) {
-            lastNetwork = network
-            ConnlibSession.reconnect(tunnelService.connlibSessionPtr!!)
-        }
         super.onLinkPropertiesChanged(network, linkProperties)
     }
 }

kotlin/android/app/src/main/java/dev/firezone/android/tunnel/TunnelService.kt

@@ -29,6 +29,7 @@ import dev.firezone.android.tunnel.model.Resource
 import java.nio.file.Files
 import java.nio.file.Paths
 import java.util.UUID
+import java.util.concurrent.locks.ReentrantLock
 import javax.inject.Inject
 
 @AndroidEntryPoint
@@ -51,6 +52,10 @@ class TunnelService : VpnService() {
     private var _tunnelState: State = State.DOWN
     private var networkCallback: NetworkMonitor? = null
 
+    // General purpose mutex lock for preventing network monitoring from calling connlib
+    // during shutdown.
+    val lock = ReentrantLock()
+
     var startedByUser: Boolean = false
     var connlibSessionPtr: Long? = null
 
@@ -131,6 +136,8 @@ class TunnelService : VpnService() {
                 Log.d(TAG, "onDisconnect: $error")
                 Firebase.crashlytics.log("onDisconnect: $error")
 
+                stopNetworkMonitoring()
+
                 // Clear any user tokens and actorNames
                 repo.clearToken()
                 repo.clearActorName()
@@ -209,19 +216,24 @@ class TunnelService : VpnService() {
     fun disconnect() {
         Log.d(TAG, "disconnect")
 
-        // Connlib should call onDisconnect() when it's done, with no error.
+        // Acquire mutex lock
+        lock.lock()
+
+        stopNetworkMonitoring()
+
         connlibSessionPtr?.let {
             ConnlibSession.disconnect(it)
         }
 
         shutdown()
+
+        // Release mutex lock
+        lock.unlock()
     }
 
     private fun shutdown() {
         Log.d(TAG, "shutdown")
 
-        stopNetworkMonitoring()
-
         connlibSessionPtr = null
         stopSelf()
         tunnelState = State.DOWN

terraform/examples/aws/nat-gateway/.terraform.lock.hcl

@@ -0,0 +1,24 @@
+# This file is maintained automatically by "terraform init".
+# Manual edits may be lost in future updates.
+
+provider "registry.terraform.io/hashicorp/aws" {
+  version = "5.55.0"
+  hashes = [
+    "h1:vChl08zNYLVzuSzfxz3wp3wNSx+vjwl/jPuyPbg59Ks=",
+    "zh:06fbb1cc4b61b9d6370d391bf7538aa6ef8b60b91c67d125a6be60a70b1d49f0",
+    "zh:1d52acd2184f379433a0fce2c29d5ed8fc7958d6a9d1b403310dcc36b2a3f626",
+    "zh:290bbce092f8836a1db530ac86d933cfea27d52b827639974a81bc48dfba8c34",
+    "zh:3531f2822c2de3ba837381c4ee4816c5b437fd204c07d659526a04d9154a65e8",
+    "zh:56d70db4c8c6c0ec1b665380b87726275f4ab3665b4b78ac86dc90e1010c0fe3",
+    "zh:8251d713c0b2c8c51b6858e51c70d083b484342ff9782a88c39e7eaa966c3da2",
+    "zh:9a7d1f7207e51382a7dd139dfd5786e7e905edf9bf89bbee4b59ad41365e87be",
+    "zh:9b12af85486a96aedd8d7984b0ff811a4b42e3d88dad1a3fb4c0b580d04fa425",
+    "zh:a529c78dfc60063289524690af78794e99a768835b88e27cdfec15bc85439f7c",
+    "zh:b6da1843355db05c5d412126406fd97db2a6ff9edc166b81c1cea2994535b4eb",
+    "zh:bfc08cd23b1556b3287d1b28ac7f12c7d459471d97a0592bf2579ea68d11bae7",
+    "zh:c382088faf05894191636b57861069a21de10a5ff4eb8f7cc122e764ccf7a4a8",
+    "zh:e27f99f389921314ee428b24990d3a829057ce532b2beb33c69387458722edd9",
+    "zh:ef11285eedb45ffc3fb2ecdfefa206e64eb2760a87fff15c44dee42de9703436",
+    "zh:fedc4ebee0d6fe196691127004db5d1ff8bd22e3b667a74026bb92c607589b6c",
+  ]
+}