The tcpwrappers package provides daemon wrapper programs that report the name of the client requesting network services and the requested service.
Download (HTTP): http://files.ichilton.co.uk/nfs/tcp_wrappers_7.6.tar.gz
Download (FTP): ftp://ftp.porcupine.org/pub/security/tcp_wrappers_7.6.tar.gz
Download size: 100 KB
Estimated Disk space required: 720 KB
Estimated build time: 0.16 SBU
Required patch (Fixes some build issues and adds building of a shared library): http://www.linuxfromscratch.org/patches/blfs/5.1/tcp_wrappers-7.6-shared-lib-plus-plus.patch
Install tcpwrappers with the following commands:
patch -Np1 -i ../tcp_wrappers-7.6-shared-lib-plus-plus.patch && make REAL_DAEMON_DIR=/usr/sbin STYLE=-DPROCESS_OPTIONS linux && make install
File protections: the wrapper, all files used by the wrapper, and all directories in the path leading to those files, should be accessible but not writable for unprivileged users (mode 755 or mode 555). Do not install the wrapper set-uid.
Then perform the following edits on the /etc/inetd.conf configuration file:
finger stream tcp nowait nobody /usr/sbin/in.fingerd in.fingerd
finger stream tcp nowait nobody /usr/sbin/tcpd in.fingerd
The finger server is used as an example here.
Similar changes must be made if xinetd is used, with the emphasis being on calling /usr/sbin/tcpd instead of calling the service daemon directly, and passing the name of the service daemon to tcpd.
The tcpwrappers package contains tcpd, tcpdchk, tcpdmatch, try-from and safe_finger.
tcpd is the main access control daemon for all Internet services, which inetd or xinetd will run instead of running the requested service daemon.
tcpdmatch is used to predict how the tcp wrapper would handle a specific request for a service.
try-from can be called via a remote shell command to find out if the host name and address are properly recognized.