Messaging doesn't allow sharing of its own files

-Previously, Messaging allowed sharing of any file it had permission
 to reach. This meant that bad apps could share a link to
 file:///data/data/com.android.messaging/databases/bugle_db
 and Messaging would happily send all this sensitive information to
 the target. Worse, a bad app could share a softlink to this file,
 where the symlink was picture.jpg with the image/jpg type.
-Now, when sanitizing attachments, we make sure any filepaths don't
 lead to any Bugle-specific directories.
-getApplicationInfo().dataDir is a symlink to
 /data/data/com.android.messaging, and appears to be the
 only directory where we store personal data.
-Most apps share as contentUris, including Messaging, so Messaging
 can still share to itself.

Change-Id: Ic464bc1f099029a030793c478aaf88b957d8bad1
Fixes:28076752

src/com/android/messaging/ui/conversationlist/ShareIntentActivity.java

@@ -34,6 +34,7 @@ import com.android.messaging.util.Assert;
 import com.android.messaging.util.ContentType;
 import com.android.messaging.util.LogUtil;
 import com.android.messaging.util.MediaMetadataRetrieverWrapper;
+import com.android.messaging.util.FileUtil;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -158,8 +159,12 @@ public class ShareIntentActivity extends BaseBugleActivity implements
     }
 
     private void addSharedImagePartToDraft(final String contentType, final Uri imageUri) {
-        mDraftMessage.addPart(PendingAttachmentData.createPendingAttachmentData(contentType,
-                imageUri));
+        if (FileUtil.isInPrivateDir(getBaseContext(), imageUri)) {
+            Assert.fail("Cannot send private file " + imageUri.toString());
+        } else {
+            mDraftMessage.addPart(PendingAttachmentData.createPendingAttachmentData(contentType,
+                    imageUri));
+        }
     }
 
     @Override