In a similar family, note also that setuid() can fail! If you try to setuid() to a user that has has reached their ulimit for number of processes, then setuid() will fail, just like fork() would for that user.

This is a classic way to get your application exploited. Google did it (at least) twice in Android: once in ADB [1], and once in Zygote [2]. Both resulted in escalation.

Check your return values! All of them!

[1] http://thesnkchrmr.wordpress.com/2011/03/24/rageagainsttheca... [2] https://github.com/unrevoked/zysploit