5.7. Other Inputs
Programs must ensure that all inputs are controlled; this is particularly difficult for setuid/setgid programs because they have so many such inputs. Other inputs programs must consider include the current directory, signals, memory maps (mmaps), System V IPC, pending timers, resource limits, the scheduling priority, and the umask (which determines the default permissions of newly-created files). Consider explicitly changing directories (using chdir(2)) to an appropriately fully named directory at program startup.