This LD_PRELOAD shared library is used to override modes given to chmod(2), fchmod(2) and fchmodat(2)
In default configuration, it will disable making files group or world writeable.

For example, on Debian system you can edit /etc/init.d/vsftpd and before
starting daemon put

LD_PRELOAD="/usr/local/lib/libchmod.so"
export LD_PRELOAD

In such configuration, on your shared web hosting machine, you could allow
'SITE CHMOD' commands in vsftpd(8) (so users can set their suexec'd CGI
scripts u+x, for example), but still disallow them to do outrageously stupid
things they're bound to do following advice on Internet forums, like doing
"chmod 777" on all files and directories "just in case" and hence opening
themselves to world of pain (and blaming *YOU* when they get cracked).