What is the ruling on kissing a parent's foot out of dutifulness to them, or obedience to them?

There is no harm in kissing the hand, foot, and head of one's father, as a sign of honor and filial piety. The same applies to people of knowledge and virtue. Several Hadith (definition) support this, including the Companions kissing the hand and foot of the Prophet (peace be upon him), a Jew kissing his hand and foot as a testimony to his prophethood, kissing the Prophet's head and feet, and kissing the Prophet's hand and knees. Ibn Hajar Al-Haytami also narrated that Ali (may Allah be pleased with him) kissed the hand and foot of Al-Abbas. Ibn Muflih mentioned that Abu Ubaidah kissed the hand and foot of Umar, and that Sufyan ibn Uyaynah and Fudayl ibn Iyad kissed Al-Husayn ibn Ali Al-Ja'fari. Al-Nawawi recommended kissing the hand, head, and foot of a righteous, ascetic, and knowledgeable man.