use private temp files to pass decrypted private keys

Android 10 (API 29) doesn't allow us to pass them by sharing file
descriptors anymore, making the use of temp files mandatory.

GitHub: https://github.com/pacien/tincapp/issues/92

3 files changed, 38 insertions, 21 deletions

diff --git a/app/src/main/java/org/pacien/tincapp/context/AppPaths.kt b/app/src/main/java/org/pacien/tincapp/context/AppPaths.kt
index 1efb7cf..2394586 100644
--- a/app/src/main/java/org/pacien/tincapp/context/AppPaths.kt
+++ b/app/src/main/java/org/pacien/tincapp/context/AppPaths.kt
@@ -1,6 +1,6 @@
 /*
  * Tinc App, an Android binding and user interface for the tinc mesh VPN daemon
- * Copyright (C) 2017-2018 Pacien TRAN-GIRARD
+ * Copyright (C) 2017-2020 Pacien TRAN-GIRARD
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -25,7 +25,7 @@ import java.io.FileNotFoundException
 /**
  * @author pacien
  *
- * @implNote Logs and PID files are stored in the cache directory for easy clean up.
+ * @implNote Logs and PID files are stored in the cache directory for automatic collection.
  */
 object AppPaths {
   private const val TINCD_BIN = "libtincd.so"
@@ -40,15 +40,16 @@ object AppPaths {
   private const val NET_TINC_CONF_FILE = "tinc.conf"
   private const val NET_HOSTS_DIR = "hosts"
   private const val NET_INVITATION_FILE = "invitation-data"
-  private const val NET_DEFAULT_ED25519_PRIVATE_KEY_FILE = "ed25519_key.priv"
-  private const val NET_DEFAULT_RSA_PRIVATE_KEY_FILE = "rsa_key.priv"
+
+  const val NET_DEFAULT_ED25519_PRIVATE_KEY_FILE = "ed25519_key.priv"
+  const val NET_DEFAULT_RSA_PRIVATE_KEY_FILE = "rsa_key.priv"
 
   private val context by lazy { App.getContext() }
 
   fun storageAvailable() =
     Environment.getExternalStorageState().let { it == Environment.MEDIA_MOUNTED && it != Environment.MEDIA_MOUNTED_READ_ONLY }
 
-  private fun internalCacheDir() = context.cacheDir!!
+  fun internalCacheDir() = context.cacheDir!!
   fun cacheDir() = context.externalCacheDir!!
   fun confDir() = context.getExternalFilesDir(null)!!
   private fun binDir() = File(context.applicationInfo.nativeLibraryDir)
diff --git a/app/src/main/java/org/pacien/tincapp/service/TincVpnService.kt b/app/src/main/java/org/pacien/tincapp/service/TincVpnService.kt
index 48cb1df..c688742 100644
--- a/app/src/main/java/org/pacien/tincapp/service/TincVpnService.kt
+++ b/app/src/main/java/org/pacien/tincapp/service/TincVpnService.kt
@@ -102,12 +102,17 @@ class TincVpnService : VpnService() {
     log.info("Starting tinc daemon for network \"$netName\".")
     if (isConnected() || getCurrentNetName() != null) stopVpn().join()
 
-    // FIXME: pass decrypted private keys via temp file
     val privateKeys = try {
       TincConfiguration.fromTincConfiguration(AppPaths.existing(AppPaths.tincConfFile(netName))).let { tincCfg ->
         Pair(
-          TincKeyring.openPrivateKey(tincCfg.ed25519PrivateKeyFile ?: AppPaths.defaultEd25519PrivateKeyFile(netName), passphrase),
-          TincKeyring.openPrivateKey(tincCfg.privateKeyFile ?: AppPaths.defaultRsaPrivateKeyFile(netName), passphrase))
+          TincKeyring.unlockKey(
+            AppPaths.NET_DEFAULT_ED25519_PRIVATE_KEY_FILE,
+            tincCfg.ed25519PrivateKeyFile ?: AppPaths.defaultEd25519PrivateKeyFile(netName),
+            passphrase),
+          TincKeyring.unlockKey(
+            AppPaths.NET_DEFAULT_RSA_PRIVATE_KEY_FILE,
+            tincCfg.privateKeyFile ?: AppPaths.defaultRsaPrivateKeyFile(netName),
+            passphrase))
       }
     } catch (e: FileNotFoundException) {
       Pair(null, null)
@@ -143,15 +148,12 @@ class TincVpnService : VpnService() {
     val serverSocket = LocalServerSocket(DEVICE_FD_ABSTRACT_SOCKET)
     Executor.runAsyncTask { serveDeviceFd(serverSocket, deviceFd) }
 
-    // FIXME: pass decrypted private keys via temp file
-    val daemon = Tincd.start(netName, DEVICE_FD_ABSTRACT_SOCKET, null, null)
+    val daemon = Tincd.start(netName, DEVICE_FD_ABSTRACT_SOCKET, privateKeys.first, privateKeys.second)
     setState(netName, passphrase, interfaceCfg, deviceFd, daemon)
 
     waitForDaemonStartup().whenComplete { _, exception ->
       serverSocket.close()
       deviceFd.close()
-      privateKeys.first?.close()
-      privateKeys.second?.close()
 
       if (exception != null) {
         reportError(resources.getString(R.string.notification_error_message_daemon_exited, exception.cause!!.defaultMessage()), exception)
diff --git a/app/src/main/java/org/pacien/tincapp/utils/TincKeyring.kt b/app/src/main/java/org/pacien/tincapp/utils/TincKeyring.kt
index bae38ac..89bb246 100644
--- a/app/src/main/java/org/pacien/tincapp/utils/TincKeyring.kt
+++ b/app/src/main/java/org/pacien/tincapp/utils/TincKeyring.kt
@@ -1,6 +1,6 @@
 /*
  * Tinc App, an Android binding and user interface for the tinc mesh VPN daemon
- * Copyright (C) 2017-2018 Pacien TRAN-GIRARD
+ * Copyright (C) 2017-2020 Pacien TRAN-GIRARD
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -18,10 +18,11 @@
 
 package org.pacien.tincapp.utils
 
-import android.os.ParcelFileDescriptor
 import org.pacien.tincapp.commands.TincApp
+import org.pacien.tincapp.context.AppPaths
 import java.io.File
 import java.io.FileNotFoundException
+import java.io.FileWriter
 
 /**
  * @author pacien
@@ -33,12 +34,25 @@ object TincKeyring {
     false
   }
 
-  fun openPrivateKey(f: File?, passphrase: String?): ParcelFileDescriptor? {
-    if (f == null || !f.exists() || passphrase == null) return null
-    val pipe = ParcelFileDescriptor.createPipe()
-    val decryptedKey = PemUtils.decrypt(PemUtils.read(f), passphrase)
-    val outputStream = ParcelFileDescriptor.AutoCloseOutputStream(pipe[1])
-    PemUtils.write(decryptedKey, outputStream.writer())
-    return pipe[0]
+  fun unlockKey(target: String, input: File?, passphrase: String?): File? {
+    if (input == null || !input.exists() || passphrase == null) return null
+    val decryptedKey = PemUtils.decrypt(PemUtils.read(input), passphrase)
+    val decryptedFile = tempKey(target)
+    PemUtils.write(decryptedKey, FileWriter(decryptedFile, false))
+    return decryptedFile
+  }
+
+  private fun tempKey(name: String): File {
+    val file = File(AppPaths.internalCacheDir(), name)
+    file.createNewFile()
+    file.deleteOnExit()
+    file.makePrivate()
+    return file
+  }
+
+  private fun File.makePrivate() {
+    this.setExecutable(false, false)
+    this.setReadable(true, true)
+    this.setWritable(true, true)
   }
 }