DisplayChdir using absolute path should work properly with DefaultRoot

[Nitczi]

What I Did

this is my first time using proftpd

I was trying to use the directive 'DisplayChdir' to set my own message but it wasn't working. So I tried to disable some options, one of these options was DefaultRoot. By disabling the DefaultRoot directive the message that was set in DisplayChdir is displayed normally.

ProFTPD Version and Configuration

I'm using the "ProFTPD Version 1.3.7rc", I just installed with sudo apt install proftpd.

This is my proftpd.conf file:

# /etc/proftpd/proftpd.conf -- This is a basic ProFTPD configuration file.
# To really apply changes, reload proftpd after modifications, if
# it runs in daemon mode. It is not required in inetd/xinetd mode.
#

# Includes DSO modules
Include /etc/proftpd/modules.conf

# Set off to disable IPv6 support which is annoying on IPv4 only boxes.
UseIPv6 off
# If set on you can experience a longer connection delay in many cases.
<IfModule mod_ident.c>
  IdentLookups off
</IfModule>

ServerName "Debian"
# Set to inetd only if you would run proftpd by inetd/xinetd/socket.
# Read README.Debian for more information on proper configuration.
ServerType standalone
DeferWelcome off

####### THESE ARE MINE ##############
RequireValidShell off
#DefaultRoot ~
####################################

# Disable MultilineRFC2228 per https://github.com/proftpd/proftpd/issues/1085
# MultilineRFC2228on
DefaultServer on
ShowSymlinks on

TimeoutNoTransfer 600
TimeoutStalled 600
TimeoutIdle 1200

DisplayLogin "/etc/proftpd/welcome.msg"
DisplayChdir "/etc/proftpd/message.msg"
ListOptions "-l"

DenyFilter \*.*/

# Use this to jail all users in their homes 
#DefaultRoot~

# Users require a valid shell listed in /etc/shells to login.
# Use this directive to release that constrain.
# RequireValidShelloff

# Port 21 is the standard FTP port.
Port 21

# In some cases you have to specify passive ports range to by-pass
# firewall limitations. Ephemeral ports can be used for that, but
# feel free to use a more narrow range.
# PassivePorts 49152 65534

# If your host was NATted, this option is useful in order to
# allow passive tranfers to work. You have to use your public
# address and opening the passive ports used on your firewall as well.
# MasqueradeAddress 1.2.3.4

# This is useful for masquerading address with dynamic IPs:
# refresh any configured MasqueradeAddress directives every 8 hours
<IfModule mod_dynmasq.c>
# DynMasqRefresh 28800
</IfModule>

# To prevent DoS attacks, set the maximum number of child processes
# to 30.  If you need to allow more than 30 concurrent connections
# at once, simply increase this value.  Note that this ONLY works
# in standalone mode, in inetd mode you should use an inetd server
# that allows you to limit maximum number of processes per service
# (such as xinetd)
MaxInstances 30

# Set the user and group that the server normally runs at.
#User proftpd
#Group nogroup

# Umask 022 is a good standard umask to prevent new files and dirs
# (second parm) from being group and world writable.
Umask 022 022
# Normally, we want files to be overwriteable.
AllowOverwrite on

# Uncomment this if you are using NIS or LDAP via NSS to retrieve passwords:
# PersistentPasswd off

# This is required to use both PAM-based authentication and local passwords
# AuthOrder mod_auth_pam.c* mod_auth_unix.c

# Be warned: use of this directive impacts CPU average load!
# Uncomment this if you like to see progress and transfer rate with ftpwho
# in downloads. That is not needed for uploads rates.
#
# UseSendFile off

TransferLog /var/log/proftpd/xferlog
SystemLog /var/log/proftpd/proftpd.log

# Logging onto /var/log/lastlog is enabled but set to off by default
#UseLastlog on

# In order to keep log file dates consistent after chroot, use timezone info
# from /etc/localtime.  If this is not set, and proftpd is configured to
# chroot (e.g. DefaultRoot or <Anonymous>), it will use the non-daylight
# savings timezone regardless of whether DST is in effect.
#SetEnv TZ :/etc/localtime

<IfModule mod_quotatab.c>
QuotaEngine off
</IfModule>

<IfModule mod_ratio.c>
Ratios off
</IfModule>


# Delay engine reduces impact of the so-called Timing Attack described in
# http://www.securityfocus.com/bid/11430/discuss
# It is on by default. 
<IfModule mod_delay.c>
DelayEngine on
</IfModule>

<IfModule mod_ctrls.c>
ControlsEngine off
ControlsMaxClients 2
ControlsLog /var/log/proftpd/controls.log
ControlsInterval 5
ControlsSocket /var/run/proftpd/proftpd.sock
</IfModule>

<IfModule mod_ctrls_admin.c>
AdminControlsEngine off
</IfModule>

#
# Alternative authentication frameworks
#
#Include /etc/proftpd/ldap.conf
#Include /etc/proftpd/sql.conf

#
# This is used for FTPS connections
#
#Include /etc/proftpd/tls.conf

#
# This is used for SFTP connections
#
#Include /etc/proftpd/sftp.conf

#
# This is used for other add-on modules
#
#Include /etc/proftpd/dnsbl.conf
#Include /etc/proftpd/geoip.conf
#Include /etc/proftpd/snmp.conf

#
# Useful to keep VirtualHost/VirtualRoot directives separated
#
#Include /etc/proftpd/virtuals.conf

# A basic anonymous configuration, no upload directories.

<Anonymous ~>
   User mark 
   Group nogroup
#   # We want clients to be able to login with "anonymous" as well as "ftp"
#   UserAlias anonymous ftp
#   # Cosmetic changes, all files belongs to ftp user
#   DirFakeUser on ftp
#   DirFakeGroup on ftp
# 
   RequireValidShell off
# 
#   # Limit the maximum number of anonymous logins
#   MaxClients 10
# 
#   # We want 'welcome.msg' displayed at login, and '.message' displayed
#   # in each newly chdired directory.
#   DisplayLogin welcome.msg
#   DisplayChdir .message
# 
#   # Limit WRITE everywhere in the anonymous chroot
#   <Directory *>
#     <Limit WRITE>
#       DenyAll
#     </Limit>
#   </Directory>
# 
#   # Uncomment this if you're brave.
#   # <Directory incoming>
#   #   # Umask 022 is a good standard umask to prevent new files and dirs
#   #   # (second parm) from being group and world writable.
#   #   Umask022  022
#   #   <Limit READ WRITE>
#   #     DenyAll
#   #     </Limit>
#   #       <Limit STOR>
#   #         AllowAll
#   #     </Limit>
#   # </Directory>
# 
</Anonymous>

# Include other custom configuration files
# !! Please note, that this statement will read /all/ file from this subdir,
# i.e. backup files created by your editor, too !!!
# Eventually create file patterns like this: /etc/proftpd/conf.d/*.conf
# 
Include /etc/proftpd/conf.d/

[Castaglia]

The DisplayChdir directive is intended to configure a file that contains a message to displayed to clients, whenever the client changes into a directory. Usually this directive is configured with just a filename, not an absolute path; the file is assumed to exist in the directory into which the client changed. Is that what you are wanting to achieve?

I ask because you currently have:

DisplayChdir "/etc/proftpd/message.msg"

which, in turn, would cause the same message to displayed every time, no matter directory the client changed into.

You configured an absolute path, which would indeed currently not work with DefaultRoot, because of the above assumption in the code that a DisplayChdir would be relative path to some file in the directory. We can make an absolute path for DisplayChdir files work, even with DefaultRoot -- it would require changing some code. But before I do so, I want to make sure what just behavior you are wanting to achieve.

[Nitczi]

My idea was: "Everytime the client change to any directory, a message will be displayed".

"You configured an absolute path, which would indeed currently not work with DefaultRoot, because of the above assumption in the code that a DisplayChdir would be relative path to some file in the directory"

This part I don't understood. Why and how the DisplayChdir, an absolute path, will not work with DefaultRoot?

[Castaglia]

This part I don't understood. Why and how the DisplayChdir, an absolute path, will not work with DefaultRoot?

If the DisplayChdir file is always a relative path, then that directive (and its file) can be looked up, opened at the time that the client issues the CWD/CDUP/XCWD/XCUP command -- and those commands happen after authentication, thus after the DefaultRoot directive is handled, and the chroot(2) done. Using chroot(2) changes the root of the filesystem -- which means that your DisplayChdir /etc/proftpd/message.msg could cause ProFTPD to actually look for a file in (say) /home/user//etc/proftpd/message.msg.

The current DisplayChdir code assumes that the configured file is always a relative path, and because of this, it does not have to take into account any DefaultRoot effects.

[Nitczi]

Got it! So in this case I should put the file message.msg in the home of the user and set the DisplayChdir as DisplayChdir message.msg?

[Castaglia]

Correct. And then, with DisplayChdir message.msg, any directory that contains a "message.msg" file would have that file displayed. So you can put different messages in different directories, as you need, as long as those messages are in files named "message.msg".

[Castaglia]

This should now work as expected in the master branch. Thanks!