What is the White Cylindracal Exposed Area That I See in my Root Canal?

If you are in the process of having a root canal treatment it is most likely a temporary filling with some medicated cotton.  The most important thing is that the temporary filling isn't leaking and allowing more bacteria from your mouth to enter the root canal opening.  Just call your dentist and tell him that the temporary filling he placed needs to be checked.

The bad taste you are experiencing is the medicament in a cotton pellet that is placed over the canals and sealed with temporary filling.  The white can be part of the cotton that is exposed due to some of the temporary washing away.  See your dentist.