(#) `openFileOutput()` with `MODE_WORLD_READABLE` !!! WARNING: `openFileOutput()` with `MODE_WORLD_READABLE` This is a warning. Id : `WorldReadableFiles` Summary : `openFileOutput()` with `MODE_WORLD_READABLE` Severity : Warning Category : Security Platform : Android Vendor : Android Open Source Project Feedback : https://issuetracker.google.com/issues/new?component=192708 Since : Initial Affects : Kotlin and Java files Editing : This check runs on the fly in the IDE editor See : https://goo.gle/WorldReadableFiles Implementation : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/SecurityDetector.java) Tests : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/SecurityDetectorTest.java) Copyright Year : 2011 There are cases where it is appropriate for an application to write world readable files, but these should be reviewed carefully to ensure that they contain no private data that is leaked to other applications. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/test/pkg/WorldWriteableFile.java:27:Warning: Using MODE_WORLD_READABLE when creating files can be risky, review carefully [WorldReadableFiles] out = openFileOutput(mFile.getName(), MODE_WORLD_READABLE); ------------------- src/test/pkg/WorldWriteableFile.java:32:Warning: Using MODE_WORLD_READABLE when creating files can be risky, review carefully [WorldReadableFiles] prefs = getSharedPreferences(mFile.getName(), MODE_WORLD_READABLE); ------------------- src/test/pkg/WorldWriteableFile.java:36:Warning: Using MODE_WORLD_READABLE when creating files can be risky, review carefully [WorldReadableFiles] dir = getDir(mFile.getName(), MODE_WORLD_READABLE); ------------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/test/pkg/WorldWriteableFile.java`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers package test.pkg; import java.io.File; import java.io.IOException; import java.io.OutputStream; import java.io.InputStream; import java.io.FileNotFoundException; import android.content.Context; import android.content.SharedPreferences; import android.app.Activity; import android.os.Bundle; public class WorldWriteableFile extends Activity { File mFile; Context mContext; public void foo() { OutputStream out = null; SharedPreferences prefs = null; File dir = null; boolean success = false; try { //out = openFileOutput(mFile.getName()); // ok out = openFileOutput(mFile.getName(), MODE_PRIVATE); // ok out = openFileOutput(mFile.getName(), MODE_WORLD_WRITEABLE); out = openFileOutput(mFile.getName(), MODE_WORLD_READABLE); prefs = getSharedPreferences(mFile.getName(), 0); // ok prefs = getSharedPreferences(mFile.getName(), MODE_PRIVATE); // ok prefs = getSharedPreferences(mFile.getName(), MODE_WORLD_WRITEABLE); prefs = getSharedPreferences(mFile.getName(), MODE_WORLD_READABLE); dir = getDir(mFile.getName(), MODE_PRIVATE); // ok dir = getDir(mFile.getName(), MODE_WORLD_WRITEABLE); dir = getDir(mFile.getName(), MODE_WORLD_READABLE); mFile.setReadable(true, true); // ok mFile.setReadable(false, true); // ok mFile.setReadable(false, false); // ok mFile.setReadable(true, false); mFile.setReadable(true); // ok mFile.setReadable(false); // ok mFile.setWritable(true, true); // ok mFile.setWritable(false, true); // ok mFile.setWritable(false, false); // ok mFile.setWritable(true, false); mFile.setWritable(true); // ok mFile.setWritable(false); // ok // Flickr.get().downloadPhoto(params[0], Flickr.PhotoSize.LARGE, // out); success = true; } catch (FileNotFoundException e) { } } } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/SecurityDetectorTest.java) for the unit tests for this check to see additional scenarios. The above example was automatically extracted from the first unit test found for this lint check, `SecurityDetector.testWorldWriteable`. To report a problem with this extracted sample, visit https://issuetracker.google.com/issues/new?component=192708. (##) Suppressing You can suppress false positives using one of the following mechanisms: * Using a suppression annotation like this on the enclosing element: ```kt // Kotlin @Suppress("WorldReadableFiles") fun method() { openFileOutput(...) } ``` or ```java // Java @SuppressWarnings("WorldReadableFiles") void method() { openFileOutput(...); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection WorldReadableFiles problematicStatement() ``` * Using a special `lint.xml` file in the source tree which turns off the check in that folder and any sub folder. A simple file might look like this: ```xml <?xml version="1.0" encoding="UTF-8"?> <lint> <issue id="WorldReadableFiles" severity="ignore" /> </lint> ``` Instead of `ignore` you can also change the severity here, for example from `error` to `warning`. You can find additional documentation on how to filter issues by path, regular expression and so on [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html). * In Gradle projects, using the DSL syntax to configure lint. For example, you can use something like ```gradle lintOptions { disable 'WorldReadableFiles' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore WorldReadableFiles ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).