How to make vsftpd uploads write only so nobody else can see them?

road hazard · 02-24-2023, 12:12 PM

I'm running an FTP server on a Pi(Raspberry Pi OS Lite). I created 2 test accounts:

Code:

useradd -m user1
useradd -m user2

....these will be remote users logging in.

On the Pi, fstab maps to some SAMBA shares on my server and when somebody ftp connects, they can read from all the folders perfectly.

I have a share that allows write access on my server:

Code:

[import]
        path = /mnt/md0/import/
        read only = no
        guest ok = yes
        guest only = yes
        browseable = yes
        force user = roadhazard
        force group = roadhazard

....and inside /mnt/mn0/import, I have an ftpupload directory....

On the Pi's fstab, my /mnt/ftpupload points to that folder:

Code:

//192.168.1.15/import/ftpupload /mnt/upload cifs username=anonymous,password=anonymous,iocharset=utf8 0 0

Two problems I'm having....

Number 1, when I ftp connect as user1, it fails when uploading to that folder. Wanting to know why exactly, I ssh'd into the Pi and I can only create files in the ftpupload if I use sudo, otherwise, I get a permission denied.

touch 1 fails with a permission error
sudo touch 1 works

Number 2

What can be done so people can upload files but they can't see them nor can anyone else. Sort of like a 1 way road/black hole for file uploads. I don't want user1 uploading files and user2 to see them.

Here's my vsftpd conf file:

(I set the umask as 555 (to mark uploads as w-w-w) but until I figure out problem 1, no way to test if that will solve my number 2 issue.)

Code:

# Example config file /etc/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.
#
#
# Run standalone?  vsftpd can run either from an inetd or as a standalone
# daemon started from an initscript.
listen=YES
#
# This directive enables listening on IPv6 sockets. By default, listening
# on the IPv6 "any" address (::) will accept connections from both IPv6
# and IPv4 clients. It is not necessary to listen on *both* IPv4 and IPv6
# sockets. If you want that (perhaps because you want to listen on specific
# addresses) then you must run two copies of vsftpd with two configuration
# files.
listen_ipv6=NO
#
# Allow anonymous FTP? (Disabled by default).
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=555
#
# 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
#
# If enabled, vsftpd will display directory listings with the time
# in  your  local  time  zone.  The default is to display GMT. The
# times returned by the MDTM FTP command are also affected by this
# option.
use_localtime=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.
# Note that the default log file location is /var/log/xferlog in this case.
#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 GeneFLIX 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 restrict local users to their home directories.  See the FAQ for
# the possible risks in this before using chroot_local_user or
# chroot_list_enable below.
chroot_local_user=YES
#
# 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().
# (Warning! chroot'ing can be very dangerous. If using chroot, make sure that
# the user does not have write access to the top level directory within the
# chroot)
#chroot_local_user=YES
#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
#
# Customization
# Some of vsftpd's settings don't fit the filesystem layout by
# default.
#
# This option should be the name of a directory which is empty.  Also, the
# directory should not be writable by the ftp user. This directory is used
# as a secure chroot() jail at times vsftpd does not require filesystem
# access.
#secure_chroot_dir=/var/run/vsftpd/empty
local_root=/mnt/
#
# This string is the name of the PAM service vsftpd will use.
pam_service_name=vsftpd
#
# This option specifies the location of the RSA certificate to use for SSL
# encrypted connections.
rsa_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
rsa_private_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
ssl_enable=NO

#
# Uncomment this to indicate that vsftpd use a utf8 filesystem.
#utf8_filesystem=YES

wpeckham · 02-24-2023, 12:30 PM

What you are doing should always be avoided if possible. Running a file transfer services on one machine that uses storage on another machine almost assures interesting issues that require lots of looking to understand, much less resolve.

Note: your title is misleading. Nothing about a file being write only makes it invisible.

In this operation the rule of least authority rules. Any restrictions on the SAMBA server come first, and you cannot override those from further down the transfer chain. Then the restriction on the RPi and any set in the transfer application (vsftp) add restriction. Then any client restrictions apply to whatever is left.

That can be fun to troubleshoot even when you have only one client, one server, and one service. Here you have one client, two servers, two services, making it far more "interesting" and not in a good way.

The rule of reliability is "keep it simple". Every complexity you include adds one or MORE points of failure.

Questions that may help clarify things:
#1 why are you using vsftp instead of something sane and secure like SSH/SFP?
#2 why are you inserting the RPi between the real server and the client? Why not run vsftp or ssh/sftp on the server with the SAMBA share and access that storage directly?
#3 Alternatively, who not home the storage ON the RPi and export directly using vsftp so all of the access control is on the RPi? It could even export it as a SAMBA/CIFS share if that is needed? (If you have an RPi 3b or prior, that is reason enough. That can work, but they can 'load up' and slow down pretty quick under multiple SAMBA connections.)

michaelk · 02-24-2023, 12:53 PM

Adding the noperm option to your fstab entry should allow any user on the Pi to access the share.

I don't know of a way to hide files in a directory if both users have read access to that directory.

Depending on how you setup guest access it is usually assigned to user nobody so I don't know why you are using force user or force group.