Well, today I had to reïnstall VSFTPD. Our server crashed and I had to reïnstall a new one.
While reinstalling VSFTP I saw that the last time I did not write anything down. So for my the next time:
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chroot_local_user=YES local_enable=YES write_enable=YES local_umask=000 local_root=/home/www/
The good news was that I did not need to alert pam. VSFTP, PAM, Winbind and the AD of microsoft worked happily together right from the start!