In a large bowl, combine the yeast mixture with the cake mix, salt and vanilla; stir well to combine. Stir in the flour; beat well. Cover bowl and let rise in a warm place for 1 hour.
Deflate dough and turn it out onto a well floured surface.
Roll dough out into a rectangle and spread with butter.
Sprinkle with cinnamon and sugar.
Roll up dough and cut into 3/4 inch thick rolls.
Place rolls in two lightly greased 9x13 inch baking pans. Cover and let rise until doubled, about 45 minutes.
Preheat oven to 350 degrees F (175 degrees C).
Bake rolls in preheated oven for 15 to 20 minutes. While rolls are baking, prepare the frosting. In a medium bowl, stir together confectioners' sugar, 1/3 cup butter, vanilla and milk.
Let rolls cool slightly then spread with frosting.