Transfer of military equipment between countries

I saw in the news that the USA is ready to transfer 250 used Stryker armored personnel carriers to Poland for just one dollar per unit. I'm interested in how the law generally regulates such agreements between states — are there any international or national legal restrictions on the transfer of military equipment even at a symbolic price? And can such equipment somehow end up in third countries later, for example, if they are resold, or is that also controlled by laws?