$2\mathrm{.}5$ Task $5$: Environment Variable and Set$-$UID Programs

Set$-$UID is an important security mechanism in Unix operating systems. When a Set$-$UID program

runs, it assumes the owner's privileges. For example, if the program's owner is root, when anyone runs

this program, the program gains the root's privileges during its execution. Set$-$UID allows us to do many

interesting things, but since it escalates the user's privilege, it is quite risky. Although the behaviors of

Set$-$UID programs are decided by their program logic, not by users, users can indeed affect the behav$-$

iors via environment variables. To understand how Set$-$UID programs are affected, let us first figure out

whether environment variables are inherited by the Set$-$UID program's process from the user's process.