A few quick notes on committing injustice vs suffering it

Let's suppose that person A is entitled to, say, one piece of cake. If person B knowingly causes person A to not have that piece of cake without the consent of person A, then person B has done person A wrong - which is what the Stoics mean by committing an injury. But it doesn't follow from this that person A has suffered an injury. If person A doesn't mind that his or her piece of cake was given to someone else or was eaten by person B, then person A hasn't suffered an injury - even though person B have commited an injury.

Now, let's imagine that person A is completely wise. This would mean that he or she is completely indifferent to things like bodily harm, poverty, sickness, reputation, insults, abuse and whatever else life or other human beings can throw at us. Obviously, it would still be possible to commit an injury in relation to a person like that - since this would simply require having the intention to harm that person. However, it would be impossible to actually harm that person. Which means that a wise person can't possibly suffer an injury.

Head of a Roman Patrician from Otricoli, c. 75-50 BCE, marble (Palazzo Torlonia, Rome)

A person who is not wise, could certainly suffer an injury, though. Any person who cares too much about avoiding pain, poverty, sickness, a bad reputation, insults, abuse etc can be harmed severely by life or by other people.

Since Stoicism wants to teach us all how to endure everything life and other people could possibly throw at us, it has often been accused of not caring enough about reducing the amount of injustice done in the world. Nothing could be further from the truth. Stoicism aims to make everybody wise and, thus, to prevent them from both doing injustice and from suffering it. But it's probably true that a Stoic would say that the best way to rescue a people from an evil ruler is not to kill the ruler - a new one will likely take over - but to either make people wise enough to endure whatever the ruler will do to them or to make the ruler wise enough to stop treating other people unfairly. Or both.