FYI, The August USENIX Security conference has a good paper that examines in depth the semantics of UID and GID setting calls for Solaris, FreeBSD and Linux. The differences are quite remarkable. Wietse Setuid Demystified, by Hao Chen, David Wagner, UC Berkeley; Drew Dean, SRI International www.cs.berkeley.edu/~daw/papers/setuid-usenix02.pdf
