1 files changed, 64 insertions, 0 deletions

diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/FileHelper.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/FileHelper.java
index 902af3932..671275823 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/FileHelper.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/FileHelper.java
@@ -22,6 +22,7 @@ import java.io.BufferedInputStream;
 import java.io.BufferedOutputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.File;
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.UnsupportedEncodingException;
@@ -32,6 +33,7 @@ import android.content.ActivityNotFoundException;
 import android.content.ContentResolver;
 import android.content.Context;
 import android.content.Intent;
+import android.content.res.AssetFileDescriptor;
 import android.database.Cursor;
 import android.graphics.Bitmap;
 import android.graphics.Point;
@@ -39,13 +41,19 @@ import android.net.Uri;
 import android.os.Build;
 import android.os.Build.VERSION_CODES;
 import android.os.Environment;
+import android.os.ParcelFileDescriptor;
 import android.provider.DocumentsContract;
 import android.provider.OpenableColumns;
 import android.support.v4.app.Fragment;
+import android.system.ErrnoException;
+import android.system.Os;
+import android.system.StructStat;
 import android.widget.Toast;
 
+import org.sufficientlysecure.keychain.Constants;
 import org.sufficientlysecure.keychain.R;
 
+import static android.system.OsConstants.S_IROTH;
 
 /** This class offers a number of helper functions for saving documents.
  *
@@ -261,6 +269,62 @@ public class FileHelper {
         return true;
     }
 
+    /**
+     * Tests whether a file is readable by others
+     */
+    @TargetApi(VERSION_CODES.LOLLIPOP)
+    public static boolean S_IROTH(int mode) {
+        return (mode & S_IROTH) == S_IROTH;
+    }
+
+    /**
+     * A replacement for ContentResolver.openInputStream() that does not allow the usage of
+     * "file" Uris that point to private files owned by the application only.
+     *
+     * This is not allowed:
+     * am start -a android.intent.action.SEND -t text/plain -n
+     * "org.sufficientlysecure.keychain.debug/org.sufficientlysecure.keychain.ui.EncryptFilesActivity" --eu
+     * android.intent.extra.STREAM
+     * file:///data/data/org.sufficientlysecure.keychain.debug/databases/openkeychain.db
+     *
+     * @throws FileNotFoundException
+     */
+    @TargetApi(VERSION_CODES.LOLLIPOP)
+    public static InputStream openInputStreamSafe(ContentResolver resolver, Uri uri)
+            throws FileNotFoundException {
+
+        // Not supported on Android < 5
+        if (Build.VERSION.SDK_INT < VERSION_CODES.LOLLIPOP) {
+            return resolver.openInputStream(uri);
+        }
+
+        String scheme = uri.getScheme();
+        if (ContentResolver.SCHEME_FILE.equals(scheme)) {
+            ParcelFileDescriptor pfd = ParcelFileDescriptor.open(
+                    new File(uri.getPath()), ParcelFileDescriptor.parseMode("r"));
+
+            try {
+                final StructStat st = Os.fstat(pfd.getFileDescriptor());
+                if (!S_IROTH(st.st_mode)) {
+                    Log.e(Constants.TAG, "File is not readable by others, aborting!");
+                    throw new FileNotFoundException("Unable to create stream");
+                }
+            } catch (ErrnoException e) {
+                Log.e(Constants.TAG, "fstat() failed: " + e);
+                throw new FileNotFoundException("fstat() failed");
+            }
+
+            AssetFileDescriptor fd = new AssetFileDescriptor(pfd, 0, -1);
+            try {
+                return fd.createInputStream();
+            } catch (IOException e) {
+                throw new FileNotFoundException("Unable to create stream");
+            }
+        } else {
+            return resolver.openInputStream(uri);
+        }
+    }
+
     public interface FileDialogCallback {
         void onFileSelected(File file, boolean checked);
     }