Buffer overflow attacks:

Answer and label all parts of the question $($a$-$b$).$

a$)$ In the context of a buffer overflow attack, what is "NOP Sledding"?

b$)$ Unlike more traditional stack smashing attacks, the "Return$-$to$-$libc" attack does not require execution of malicious code on the stack. How does the attack work so that the attacker gets a shell on the target machine?