Break standard network functions using LD_PRELOAD.
$ gcc -shared -fPIC nonetwork.c -o nonetwork.so
$ LD_PRELOAD=./nonetwork.so wget http://ip4.me
--2015-11-09 22:21:08-- http://ip4.me/
Resolving ip4.me (ip4.me)... failed: Non-recoverable failure in name resolution.
wget: unable to resolve host address `ip4.me'
Do not use for sandboxing and security! The network access can be easily
re-enabled, e.g. by removing LD_PRELOAD environment variable.