Catechism of the Catholic Church §1767 — excerpt
In themselves passions are neither good nor evil. They are morally qualified only to the extent that they effectively engage reason and will. Passions are said to be voluntary, "either because they are commanded by the will or because the will does not place obstacles in their way."
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: St. Thomas Aquinas, STh I-II, 24, 1 corp. art · St. Thomas Aquinas, STh I-II, 24, 3