1) We didn't give away any land to China. Almost every scholar holds that, to the contrary, it was Pakistan which acquired 750 sq. miles of administered territory.
2) International law permits a State in de facto and effective possession of an area to conclude agreements of a limited local character to maintain peace and tranquility
The Sino Pak border agreement of 1963 is Provisional , The article 6 clearly states :
“The two parties have agreed that after the settlement of the Kashmir dispute between Pakistan and India, the sovereign authority concerned will reopen negotiations with the Government of the People’s Republic of China on the boundary, as described in Article Two of the present agreement, .."
No violation of The UN Resolutions or International Law by Pakistan.