Vsftpd en Centos5

Un pequeño apunte para tener un servidor de ftp lo más rápido posible, lo cual quiere decir que seguramente no es la mejor manera. Pasos a seguir para instalar Vsftpd (Very Secure FTPD) en entorno RedHat, Centos 5 utilizando el repositorio de Centos:

# yum install vsftpd

En principio, el entorno que yo quiero es usuarios anónimos deshabilitados, cierto tipo de usuario de sistema habilitado y enjaulado en su home directory. Para eso, hacemos lo siguiente. Editamos el fichero:

# vim /etc/vsftpd/vsftpd.conf

# Example config file /etc/vsftpd/vsftpd.conf
#
# The default compiled in settings are fairly paranoid. This sample file
# loosens things up a bit, to make the ftp daemon more usable.
# Please see vsftpd.conf.5 for all compiled in defaults.
#
# READ THIS: This example file is NOT an exhaustive list of vsftpd options.
# Please read the vsftpd.conf.5 manual page to get a full idea of vsftpd's
# capabilities.
#
# Allow anonymous FTP? (Beware - allowed by default if you comment this out).
anonymous_enable=NO
#
# Uncomment this to allow local users to log in.
local_enable=YES
#
# Uncomment this to enable any form of FTP write command.
write_enable=YES
#
# Default umask for local users is 077. You may wish to change this to 022,
# if your users expect that (022 is used by most other ftpd's)
local_umask=022
#
# Uncomment this to allow the anonymous FTP user to upload files. This only
# has an effect if the above global write enable is activated. Also, you will
# obviously need to create a directory writable by the FTP user.
#anon_upload_enable=YES
#
# Uncomment this if you want the anonymous FTP user to be able to create
# new directories.
#anon_mkdir_write_enable=YES
#
# Activate directory messages - messages given to remote users when they
# go into a certain directory.
dirmessage_enable=YES
#
# Activate logging of uploads/downloads.
xferlog_enable=YES
#
# Make sure PORT transfer connections originate from port 20 (ftp-data).
connect_from_port_20=YES
#
# If you want, you can arrange for uploaded anonymous files to be owned by
# a different user. Note! Using "root" for uploaded files is not
# recommended!
#chown_uploads=YES
#chown_username=whoever
#
# You may override where the log file goes if you like. The default is shown
# below.
#xferlog_file=/var/log/vsftpd.log
#
# If you want, you can have your log file in standard ftpd xferlog format
xferlog_std_format=YES
#
# You may change the default value for timing out an idle session.
#idle_session_timeout=600
#
# You may change the default value for timing out a data connection.
#data_connection_timeout=120
#
# It is recommended that you define on your system a unique user which the
# ftp server can use as a totally isolated and unprivileged user.
#nopriv_user=ftpsecure
#
# Enable this and the server will recognise asynchronous ABOR requests. Not
# recommended for security (the code is non-trivial). Not enabling it,
# however, may confuse older FTP clients.
#async_abor_enable=YES
#
# By default the server will pretend to allow ASCII mode but in fact ignore
# the request. Turn on the below options to have the server actually do ASCII
# mangling on files when in ASCII mode.
# Beware that on some FTP servers, ASCII support allows a denial of service
# attack (DoS) via the command "SIZE /big/file" in ASCII mode. vsftpd
# predicted this attack and has always been safe, reporting the size of the
# raw file.
# ASCII mangling is a horrible feature of the protocol.
#ascii_upload_enable=YES
#ascii_download_enable=YES
#
# You may fully customise the login banner string:
#ftpd_banner=Welcome to blah FTP service.
#
# You may specify a file of disallowed anonymous e-mail addresses. Apparently
# useful for combatting certain DoS attacks.
#deny_email_enable=YES
# (default follows)
#banned_email_file=/etc/vsftpd/banned_emails
#
# You may specify an explicit list of local users to chroot() to their home
# directory. If chroot_local_user is YES, then this list becomes a list of
# users to NOT chroot().
chroot_list_enable=YES
# (default follows)
chroot_list_file=/etc/vsftpd/chroot_list
#
# You may activate the "-R" option to the builtin ls. This is disabled by
# default to avoid remote users being able to cause excessive I/O on large
# sites. However, some broken FTP clients such as "ncftp" and "mirror" assume
# the presence of the "-R" option, so there is a strong case for enabling it.
#ls_recurse_enable=YES
#
# When "listen" directive is enabled, vsftpd runs in standalone mode and
# listens on IPv4 sockets. This directive cannot be used in conjunction
# with the listen_ipv6 directive.
listen=YES
#
# This directive enables listening on IPv6 sockets. To listen on IPv4 and IPv6
# sockets, you must run two copies of vsftpd whith two configuration files.
# Make sure, that one of the listen options is commented !!
#listen_ipv6=YES
pam_service_name=vsftpd
userlist_enable=YES
userlist_deny=NO
userlist_file=/etc/vsftpd/user_list
tcp_wrappers=YES

En negrita están las directivas necesarias para lograr lo que queremos.

• anonymous_enable=NO
• local_enable=YES
• write_enable=YES

Está bastante claro lo que quieren decir, prohibimos accesos anónimos al servidor ftp. Habilitamos usuarios locales y que puedan escribir en su directorio.

• chroot_list_enable=YES
• chroot_list_file=/etc/vsftpd/chroot_list

Con chroot_list_enable, decimos que queremos que los usuarios que puedan acceder al servicio FTP, estén enjaulados en su home directory. Además, le especificamos al servidor que usuarios van a ser enjaulados, usando el archivo chroot_list.

• userlist_enable=YES
• userlist_deny=NO
• userlist_file=/etc/vsftpd/user_list

Ahora, vamos a limitar los usuarios que van a acceder al FTP. Si hacemos un cat de user_list nos lo explica bien

# vsftpd userlist
# If userlist_deny=NO, only allow users in this file
# If userlist_deny=YES (default), never allow users in this file, and
# do not even prompt for a password.
# Note that the default vsftpd pam config also checks /etc/vsftpd/ftpusers
# for users that are denied.

Es decir, para especificar con user_list el usuario que queremos que tenga acceso, la directiva userlist_deny será igual a NO. Añadimos nuestro usuario en el archivo y guardamos. Daros cuenta que userlist_enable y userlist_deny utilizan el mismo archivo, el que especificamos en userlist_file. Por otro lado, sobre el tema de enjaular el usuario, debemos editar el choroot_list y añadir nuestro usuario también.

Reiniciamos VSFTPd y ya tendremos nuestro servidor listo. Sólo quedaría revisar algunos temas de permisos.

# /etc/init.d/vsftpd restart

Links:

• http://www.brennan.id.au/14-FTP_Server.html
• http://www.ulfix.net/content/view/31/112/