Dont allow encryption of app files via Os methods (OKC-01-010)

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/SignEncryptOperation.java

@@ -17,9 +17,17 @@
 
 package org.sufficientlysecure.keychain.operations;
 
+import android.annotation.TargetApi;
+import android.content.ContentResolver;
 import android.content.Context;
+import android.content.res.AssetFileDescriptor;
 import android.net.Uri;
+import android.os.Build;
+import android.os.ParcelFileDescriptor;
 import android.support.annotation.NonNull;
+import android.system.ErrnoException;
+import android.system.Os;
+import android.system.StructStat;
 
 import org.sufficientlysecure.keychain.Constants;
 import org.sufficientlysecure.keychain.operations.results.OperationResult.LogType;
@@ -42,19 +50,24 @@ import org.sufficientlysecure.keychain.util.ProgressScaler;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
+import java.io.File;
 import java.io.FileNotFoundException;
+import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.concurrent.atomic.AtomicBoolean;
 
-/** This is a high-level operation, which encapsulates one or more sign/encrypt
+import static android.system.OsConstants.S_IFMT;
+import static android.system.OsConstants.S_IROTH;
+
+/**
+ * This is a high-level operation, which encapsulates one or more sign/encrypt
  * operations, using URIs or byte arrays as input and output.
  *
  * This operation is fail-fast: If any sign/encrypt sub-operation fails or returns
  * a pending result, it will terminate.
- *
  */
 public class SignEncryptOperation extends BaseOperation<SignEncryptParcel> {
 
@@ -63,6 +76,63 @@ public class SignEncryptOperation extends BaseOperation<SignEncryptParcel> {
         super(context, providerHelper, progressable, cancelled);
     }
 
+
+    /**
+     * Tests whether a file is readable by others
+     */
+    @TargetApi(Build.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(Build.VERSION_CODES.LOLLIPOP)
+    private InputStream openInputStreamSafe(ContentResolver resolver, Uri uri)
+            throws FileNotFoundException {
+
+        // Not supported on Android < 5
+        if (Build.VERSION.SDK_INT < Build.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);
+        }
+    }
+
     @NonNull
     public SignEncryptResult execute(SignEncryptParcel input, CryptoInputParcel cryptoInput) {
 
@@ -115,7 +185,7 @@ public class SignEncryptOperation extends BaseOperation<SignEncryptParcel> {
                     log.add(LogType.MSG_SE_INPUT_URI, 1);
                     Uri uri = inputUris.removeFirst();
                     try {
-                        InputStream is = mContext.getContentResolver().openInputStream(uri);
+                        InputStream is = openInputStreamSafe(mContext.getContentResolver(), uri);
                         long fileSize = FileHelper.getFileSize(mContext, uri, 0);
                         String filename = FileHelper.getFilename(mContext, uri);
                         inputData = new InputData(is, fileSize, filename);