RootShell: Use the application cache dir as TMPDIR

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/src/main/java/com/wireguard/android/ProfileService.java

@@ -29,6 +29,7 @@ public class ProfileService extends Service {
 
     private final IBinder binder = new ProfileServiceBinder();
     private final ObservableList<Profile> profiles = new ObservableArrayList<>();
+    private RootShell rootShell;
 
     @Override
     public IBinder onBind(Intent intent) {
@@ -37,6 +38,7 @@ public class ProfileService extends Service {
 
     @Override
     public void onCreate() {
+        rootShell = new RootShell(this);
         new ProfileLoader().execute(getFilesDir().listFiles(new FilenameFilter() {
             @Override
             public boolean accept(File dir, String name) {
@@ -94,7 +96,7 @@ public class ProfileService extends Service {
         protected Boolean doInBackground(Void... voids) {
             Log.i(TAG, "Running wg-quick up for profile " + profile.getName());
             final File configFile = new File(getFilesDir(), profile.getName() + ".conf");
-            return RootShell.run(null, "wg-quick up '" + configFile.getPath() + "'") == 0;
+            return rootShell.run(null, "wg-quick up '" + configFile.getPath() + "'") == 0;
         }
 
         @Override
@@ -117,7 +119,7 @@ public class ProfileService extends Service {
         protected Boolean doInBackground(Void... voids) {
             Log.i(TAG, "Running wg-quick down for profile " + profile.getName());
             final File configFile = new File(getFilesDir(), profile.getName() + ".conf");
-            return RootShell.run(null, "wg-quick down '" + configFile.getPath() + "'") == 0;
+            return rootShell.run(null, "wg-quick down '" + configFile.getPath() + "'") == 0;
         }
 
         @Override
@@ -134,7 +136,7 @@ public class ProfileService extends Service {
             final List<String> interfaceNames = new LinkedList<>();
             final List<Profile> loadedProfiles = new LinkedList<>();
             final String command = "wg show interfaces";
-            if (RootShell.run(interfaceNames, command) == 0 && interfaceNames.size() == 1) {
+            if (rootShell.run(interfaceNames, command) == 0 && interfaceNames.size() == 1) {
                 // wg puts all interface names on the same line. Split them into separate elements.
                 final String nameList = interfaceNames.get(0);
                 Collections.addAll(interfaceNames, nameList.split(" "));

app/src/main/java/com/wireguard/android/RootShell.java

@@ -1,5 +1,6 @@
 package com.wireguard.android;
 
+import android.content.Context;
 import android.util.Log;
 
 import java.io.BufferedReader;
@@ -19,9 +20,16 @@ class RootShell {
      * Setup commands that are run at the beginning of each root shell. The trap command ensures
      * access to the return value of the last command, since su itself always exits with 0.
      */
-    private static final String SETUP = "export TMPDIR=/data/local/tmp\ntrap 'echo $?' EXIT\n";
+    private static final String SETUP = "export TMPDIR=%s\ntrap 'echo $?' EXIT\n";
     private static final String TAG = "RootShell";
 
+    private final byte setupCommands[];
+
+    RootShell(Context context) {
+        final String tmpdir = context.getCacheDir().getPath();
+        setupCommands = String.format(SETUP, tmpdir).getBytes(StandardCharsets.UTF_8);
+    }
+
     /**
      * Run a series of commands in a root shell. These commands are all sent to the same shell
      * process, so they can be considered a shell script.
@@ -31,7 +39,7 @@ class RootShell {
      * @param commands One or more commands to run as root (each element is a separate line).
      * @return The exit value of the last command run, or -1 if there was an internal error.
      */
-    static int run(List<String> output, String... commands) {
+    int run(List<String> output, String... commands) {
         if (commands.length < 1)
             throw new IndexOutOfBoundsException("At least one command must be supplied");
         int exitValue = -1;
@@ -39,7 +47,7 @@ class RootShell {
             final ProcessBuilder builder = new ProcessBuilder().redirectErrorStream(true);
             final Process process = builder.command("su").start();
             final OutputStream stdin = process.getOutputStream();
-            stdin.write(SETUP.getBytes(StandardCharsets.UTF_8));
+            stdin.write(setupCommands);
             for (String command : commands)
                 stdin.write(command.concat("\n").getBytes(StandardCharsets.UTF_8));
             stdin.close();