Cinnamon doesn't go bad as in becoming unsafe to eat or become moldy.
However cinnamon does lose it's potency and flavor over time which means that as the cinnamon gets older it becomes less flavorful the longer it's kept.
It's best to use cinnamon within a few years of buying it and replace it with fresh cinnamon after a few years.
Spices including cinnamon unlike other foods don't go bad in a way that will make you sick if you eat it but it's best to use fresh spices and cinnamon for the best flavor.
Cinnamon is considered to have gone bad when it has a very faint or almost no aroma to it although it's still safe to consume.
Whole cinnamon sticks last longer than ground cinnamon.
Cinnamon is best stored in an airtight container in a cool and dark place to maximize it's shelf life.
Using expired cinnamon is safe as spices including cinnamon don't truly expire in the sense of becoming unsafe to eat.
However cinnamon and other spices lose flavor and aroma the longer they are kept past expiration due to the loss of essential oils over time.
So the dish you use the expired cinnamon and other spices in may not turn out as good as it would if you used fresh cinnamon and other fresh spices.