mdm: support split tunneling configuration via syspolicy (#441)

Updates tailscale/tailscale#6912

Adds two new Android-only MDM policies: IncludedPackageNames and ExcludedPackageNames. These are comma-separated string values that contain Android package names to configure app-based split tunneling programmatically.

If ExcludedPackageNames is non-empty, Tailscale will exclude the given apps from the VPN tunnel.

If IncludedPackageNames is non-empty, Tailscale will configure the VPN tunnel to only route the given apps via Tailscale.

Signed-off-by: Andrea Gottardo <andrea@gottardo.me>

android/src/main/java/com/tailscale/ipn/App.kt

@@ -510,6 +510,11 @@ open class UninitializedApp : Application() {
   }
 
   fun disallowedPackageNames(): List<String> {
+    val mdmDisallowed = MDMSettings.excludedPackages.flow.value?.split(",")?.map { it.trim() } ?: emptyList()
+    if (mdmDisallowed.isNotEmpty()) {
+      Log.d(TAG, "Excluded application packages were set via MDM: $mdmDisallowed")
+      return builtInDisallowedPackageNames + mdmDisallowed
+    }
     val userDisallowed =
         getUnencryptedPrefs().getStringSet(DISALLOWED_APPS_KEY, emptySet())?.toList() ?: emptyList()
     return builtInDisallowedPackageNames + userDisallowed

android/src/main/java/com/tailscale/ipn/IPNService.kt

@@ -9,6 +9,7 @@ import android.net.VpnService
 import android.os.Build
 import android.system.OsConstants
 import android.util.Log
+import com.tailscale.ipn.mdm.MDMSettings
 import libtailscale.Libtailscale
 import java.util.UUID
 
@@ -114,13 +115,25 @@ open class IPNService : VpnService(), libtailscale.IPNService {
     }
     b.setUnderlyingNetworks(null) // Use all available networks.
 
-    // Prevent certain apps from getting their traffic + DNS routed via Tailscale:
+    val includedPackages: List<String> =
+        MDMSettings.includedPackages.flow.value?.split(",")?.map { it.trim() } ?: emptyList()
+    if (includedPackages.isNotEmpty()) {
+      // If an admin defined a list of packages that are exclusively allowed to be used via
+      // Tailscale,
+      // then only allow those apps.
+      for (packageName in includedPackages) {
+        Log.d(TAG, "Including app: $packageName")
+        b.addAllowedApplication(packageName)
+      }
+    } else {
+      // Otherwise, prevent certain apps from getting their traffic + DNS routed via Tailscale:
       // - any app that the user manually disallowed in the GUI
       // - any app that we disallowed via hard-coding
       for (disallowedPackageName in UninitializedApp.get().disallowedPackageNames()) {
         Log.d(TAG, "Disallowing app: $disallowedPackageName")
         disallowApp(b, disallowedPackageName)
       }
+    }
 
     return VPNServiceBuilder(b)
   }

android/src/main/java/com/tailscale/ipn/mdm/MDMSettings.kt

@@ -83,6 +83,12 @@ object MDMSettings {
   val allowedSuggestedExitNodes =
       StringArrayListMDMSetting("AllowedSuggestedExitNodes", "Allowed Suggested Exit Nodes")
 
+  // Allows admins to define a list of packages that won't be routed via Tailscale.
+  val excludedPackages = StringMDMSetting("ExcludedPackageNames", "Excluded Package Names")
+  // Allows admins to define a list of packages that will be routed via Tailscale, letting all other
+  // apps skip the VPN tunnel.
+  val includedPackages = StringMDMSetting("IncludedPackageNames", "Included Package Names")
+
   val allSettings by lazy {
     MDMSettings::class
         .declaredMemberProperties

android/src/main/java/com/tailscale/ipn/ui/view/SplitTunnelAppPickerView.kt

@@ -37,6 +37,8 @@ fun SplitTunnelAppPickerView(
   val installedApps by model.installedApps.collectAsState()
   val excludedPackageNames by model.excludedPackageNames.collectAsState()
   val builtInDisallowedPackageNames: List<String> = App.get().builtInDisallowedPackageNames
+  val mdmIncludedPackages by model.mdmIncludedPackages.collectAsState()
+  val mdmExcludedPackages by model.mdmExcludedPackages.collectAsState()
 
   Scaffold(topBar = { Header(titleRes = R.string.split_tunneling, onBack = backToSettings) }) {
       innerPadding ->
@@ -50,6 +52,21 @@ fun SplitTunnelAppPickerView(
                           .selected_apps_will_access_the_internet_directly_without_using_tailscale))
             })
       }
+      if (mdmExcludedPackages?.isNotEmpty() == true) {
+        item("mdmExcludedNotice") {
+          ListItem(
+              headlineContent = {
+                Text(stringResource(R.string.certain_apps_are_not_routed_via_tailscale))
+              })
+        }
+      } else if (mdmIncludedPackages?.isNotEmpty() == true) {
+        item("mdmIncludedNotice") {
+          ListItem(
+              headlineContent = {
+                Text(stringResource(R.string.only_specific_apps_are_routed_via_tailscale))
+              })
+        }
+      } else {
         item("resolversHeader") {
           Lists.SectionDivider(
               stringResource(R.string.count_excluded_apps, excludedPackageNames.count()))
@@ -91,3 +108,4 @@ fun SplitTunnelAppPickerView(
       }
     }
   }
+}

android/src/main/java/com/tailscale/ipn/ui/viewModel/SplitTunnelAppPickerViewModel.kt

@@ -5,6 +5,7 @@ package com.tailscale.ipn.ui.viewModel
 
 import androidx.lifecycle.ViewModel
 import com.tailscale.ipn.App
+import com.tailscale.ipn.mdm.MDMSettings
 import com.tailscale.ipn.ui.util.InstalledApp
 import com.tailscale.ipn.ui.util.InstalledAppsManager
 import com.tailscale.ipn.ui.util.set
@@ -15,13 +16,15 @@ class SplitTunnelAppPickerViewModel : ViewModel() {
   val installedAppsManager = InstalledAppsManager(packageManager = App.get().packageManager)
   val excludedPackageNames: StateFlow<List<String>> = MutableStateFlow(listOf())
   val installedApps: StateFlow<List<InstalledApp>> = MutableStateFlow(listOf())
+  val mdmExcludedPackages: StateFlow<String?> = MDMSettings.excludedPackages.flow
+  val mdmIncludedPackages: StateFlow<String?> = MDMSettings.includedPackages.flow
 
   init {
     installedApps.set(installedAppsManager.fetchInstalledApps())
     excludedPackageNames.set(
         App.get()
             .disallowedPackageNames()
-            .intersect(installedApps.value.map { it.packageName })
+            .intersect(installedApps.value.map { it.packageName }.toSet())
             .toList())
   }
 

android/src/main/res/values/strings.xml

@@ -277,4 +277,10 @@
     <string name="exclude_certain_apps_from_using_tailscale">Exclude certain apps from using Tailscale</string>
     <string name="selected_apps_will_access_the_internet_directly_without_using_tailscale">Apps selected here will access the Internet directly, without using Tailscale.</string>
     <string name="count_excluded_apps">Excluded apps (%1$s)</string>
+    <string name="certain_apps_are_not_routed_via_tailscale">Certain apps are not routed via Tailscale on this device. This setting is managed by your organization and cannot be changed by you. For more information, contact your network administrator.</string>
+    <string name="only_specific_apps_are_routed_via_tailscale">Only specific apps are routed via Tailscale on this device. This setting is managed by your organization and cannot be changed by you. For more information, contact your network administrator.</string>
+    <string name="specifies_a_list_of_apps_that_will_be_excluded_from_tailscale_routes_and_dns_even_when_tailscale_is_running_all_other_apps_will_use_tailscale">Specifies a list of apps that will be excluded from Tailscale routes and DNS even when Tailscale is running. All other apps will use Tailscale.</string>
+    <string name="specifies_a_list_of_apps_that_will_always_use_tailscale_routes_and_dns_when_tailscale_is_running_all_other_apps_won_t_use_tailscale_if_this_value_is_non_empty">Specifies a list of apps that will always use Tailscale routes and DNS when Tailscale is running. All other apps won\'t use Tailscale if this value is non-empty.</string>
+    <string name="included_packages">Included packages</string>
+    <string name="excluded_packages">Excluded packages</string>
 </resources>

android/src/main/res/xml/app_restrictions.xml

@@ -110,4 +110,16 @@
         android:key="RunExitNode"
         android:restrictionType="choice"
         android:title="@string/run_as_exit_node_visibility" />
+
+    <restriction
+        android:description="@string/specifies_a_list_of_apps_that_will_be_excluded_from_tailscale_routes_and_dns_even_when_tailscale_is_running_all_other_apps_will_use_tailscale"
+        android:key="ExcludedPackageNames"
+        android:restrictionType="string"
+        android:title="@string/excluded_packages" />
+
+    <restriction
+        android:description="@string/specifies_a_list_of_apps_that_will_always_use_tailscale_routes_and_dns_when_tailscale_is_running_all_other_apps_won_t_use_tailscale_if_this_value_is_non_empty"
+        android:key="IncludedPackageNames"
+        android:restrictionType="string"
+        android:title="@string/included_packages" />
 </restrictions>