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syncthing-android
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Code Releases Activity

Fix root permission issues (fixes #812) 

* Provided fix for issue #812

Check permissions of config.xml before reading or writing from/to it.
If the permissions are wrong, assume root magic is going on, and fix it.

* Various fixes regarding coding guideline

- Fixed whitespaces
- Moved aux method to bottom of file
- Added Javadoc-like comments

* SettingsActivity: Use onClickListener for the useRoot Checkbox

* Moved fixAppDataPermissions() to class Util

* Removed obsolete shell commands

* Implemented Nutomic's changes
This commit is contained in:
Alexander Lochmann 2017-09-21 05:22:20 +02:00 committed by Felix Ableitner
parent f4d534df8e
commit f6cfab0a5f
3 changed files with 91 additions and 11 deletions
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7
src/main/java/com/nutomic/syncthingandroid/activities/SettingsActivity.java
View File

@ -24,6 +24,7 @@ import com.nutomic.syncthingandroid.model.Options;
import com.nutomic.syncthingandroid.service.RestApi;
import com.nutomic.syncthingandroid.service.SyncthingService;
import com.nutomic.syncthingandroid.util.Languages;
import com.nutomic.syncthingandroid.util.Util;
import com.nutomic.syncthingandroid.views.WifiSsidPreference;
import java.security.InvalidParameterException;
@ -155,7 +156,7 @@ public class SettingsActivity extends SyncthingActivity {
environmentVariables.setOnPreferenceChangeListener(this);
stReset.setOnPreferenceClickListener(this);
mUseRoot.setOnPreferenceChangeListener(this);
mUseRoot.setOnPreferenceClickListener(this);
useWakelock.setOnPreferenceChangeListener(this::onRequireRestart);
foregroundService.setOnPreferenceChangeListener(this::onRequireRestart);
useTor.setOnPreferenceChangeListener(this::onRequireRestart);
@ -406,9 +407,7 @@ public class SettingsActivity extends SyncthingActivity {
private class ChownFilesRunnable implements Runnable {
@Override
public void run() {
String f = getActivity().getFilesDir().getAbsolutePath();
List<String> out = Shell.SU.run("chown -R --reference=" + f + " " + f);
Log.i(TAG, "Changed owner of syncthing files, output: " + out);
Util.fixAppDataPermissions(getActivity());
}
}

33
src/main/java/com/nutomic/syncthingandroid/util/ConfigXml.java
View File

@ -1,6 +1,9 @@
package com.nutomic.syncthingandroid.util;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager.NameNotFoundException;
import android.os.Build;
import android.os.Environment;
import android.text.TextUtils;
@ -8,6 +11,8 @@ import android.util.Log;
import com.nutomic.syncthingandroid.R;
import com.nutomic.syncthingandroid.service.SyncthingRunnable;
import com.nutomic.syncthingandroid.service.SyncthingService;
import com.nutomic.syncthingandroid.util.Util;
import org.mindrot.jbcrypt.BCrypt;
import org.w3c.dom.Document;
@ -18,6 +23,7 @@ import org.xml.sax.SAXException;
import java.io.File;
import java.io.IOException;
import java.io.DataOutputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Locale;
@ -31,6 +37,7 @@ import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import eu.chainfire.libsuperuser.Shell;
/**
* Provides direct access to the config.xml file in the file system.
*
@ -63,12 +70,7 @@ public class ConfigXml {
generateKeysConfig(context);
}
try {
DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();
mConfig = db.parse(mConfigFile);
} catch (SAXException | ParserConfigurationException | IOException e) {
throw new OpenConfigException();
}
readConfig();
if (isFirstStart) {
changeLocalDeviceName();
@ -76,6 +78,20 @@ public class ConfigXml {
}
}
private void readConfig() {
if (!mConfigFile.canRead() && !Util.fixAppDataPermissions(mContext)) {
throw new OpenConfigException();
}
try {
DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();
Log.d(TAG, "Trying to read '" + mConfigFile + "'");
mConfig = db.parse(mConfigFile);
} catch (SAXException | ParserConfigurationException | IOException e) {
Log.w(TAG, "Cannot read '" + mConfigFile + "'", e);
throw new OpenConfigException();
}
}
private void generateKeysConfig(Context context) {
new SyncthingRunnable(context, SyncthingRunnable.Command.generate).run();
}
@ -216,6 +232,10 @@ public class ConfigXml {
* Writes updated mConfig back to file.
*/
private void saveChanges() {
if (!mConfigFile.canWrite() && !Util.fixAppDataPermissions(mContext)) {
Log.w(TAG, "Failed to save updated config. Cannot change the owner of the config file.");
return;
}
try {
Log.i(TAG, "Writing updated config back to file");
TransformerFactory transformerFactory = TransformerFactory.newInstance();
@ -227,5 +247,4 @@ public class ConfigXml {
Log.w(TAG, "Failed to save updated config", e);
}
}
}

62
src/main/java/com/nutomic/syncthingandroid/util/Util.java
View File

@ -4,13 +4,23 @@ import android.content.ClipData;
import android.content.ClipboardManager;
import android.content.Context;
import android.widget.Toast;
import android.util.Log;
import android.content.Context;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager.NameNotFoundException;
import java.io.IOException;
import java.io.DataOutputStream;
import com.nutomic.syncthingandroid.R;
import java.text.DecimalFormat;
import eu.chainfire.libsuperuser.Shell;
public class Util {
private static final String TAG = "SyncthingUtil";
private Util() {
}
@ -55,4 +65,56 @@ public class Util {
return new DecimalFormat("#,##0.#")
.format(bytes / Math.pow(1024, digitGroups)) + " " + units[digitGroups];
}
/**
* Normally an application's data directory is only accessible by the corresponding application.
* Therefore, every file and directory is owned by an application's user and group. When running Syncthing as root,
* it writes to the application's data directory. This leaves files and directories behind which are owned by root having 0600.
* Moreover, those acitons performed as root changes a file's type in terms of SELinux.
* A subsequent start of Syncthing will fail due to insufficient permissions.
* Hence, this method fixes the owner, group and the files' type of the data directory.
*
* @return true if the operation was successfully performed. False otherwise.
*/
public static boolean fixAppDataPermissions(Context context) {
// We can safely assume that root magic is somehow available, because readConfig and saveChanges check for
// read and write access before calling us.
// Be paranoid :) and check if root is available.
// Ignore the 'use_root' preference, because we might want to fix ther permission
// just after the root option has been disabled.
if (!Shell.SU.available()) {
Log.e(TAG, "Root is not available. Cannot fix permssions.");
return false;
}
try {
ApplicationInfo appInfo = context.getPackageManager().getApplicationInfo(context.getPackageName(), 0);
Log.d(TAG, "Uid of '" + context.getPackageName() + "' is " + appInfo.uid);
Process fixPerm = Runtime.getRuntime().exec("su");
DataOutputStream fixPermOut = new DataOutputStream(fixPerm.getOutputStream());
String dir = context.getFilesDir().getAbsolutePath();
String cmd = "chown -R " + appInfo.uid + ":" + appInfo.uid + " " + dir + "\n";
Log.d(TAG, "Running: '" + cmd);
fixPermOut.writeBytes(cmd);
// Running Syncthing as root might change a file's or directories type in terms of SELinux.
// Leaving them as they are, the Android service won't be able to access them.
// At least for those files residing in an application's data folder.
// Simply reverting the type to its default should do the trick.
cmd = "restorecon -R " + dir + "\n";
Log.d(TAG, "Running: '" + cmd);
fixPermOut.writeBytes(cmd);
fixPermOut.flush();
fixPermOut.close();
int ret = fixPerm.waitFor();
Log.i(TAG, "Changed the owner, the group and the SELinux context of '" + dir + "'. Result: " + ret);
return ret == 0;
} catch (IOException | InterruptedException e) {
Log.w(TAG, "Cannot chown data directory", e);
} catch (NameNotFoundException e) {
// This should not happen!
// One should always be able to retrieve the application info for its own package.
Log.w(TAG, "This should not happen", e);
}
return false;
}
}