RHEL6 – How to Setup an Anonymous Download Only FTP Server

Sticker,375x360A while back I spit out a post on how to configure an anonymous ftp server that allowed uploads and downloads, which you can find here.

Its a very exciting read and will tell you everything that you need to know to get you up and running with an anonymous ftp server. However those instructions are specifically for a server that allows anonymous uploads as well as downloads. So today we are going to go over only the steps for anonymous download, which is actually much easier.

Basic Install & Configuration

So first lets install vsftp.

# yum -y install vsftpd && service vsftpd start && chkconfig vsftpd on

Then edit /etc/vsftp/vsftpd.conf and make sure that the following line is uncommented.

anonymous_enable=YES

You should also be aware of the following configuration directive. By setting local enable to no in /etc/vsftp/vsftpd.conf, you disallow local Unix users access to ftp, which ensures that your ftp server is truly anonymous only.

local_enable=no

Now restart vsftpd and you should be in business

Testing Anonymous Download

To test ftp you need an ftp client, which can be installed via yum as seen below.

yum -y install ftp

Then you should be able to ftp to localhost like as seen below and get a file. Note that an anonymous login does not a password

# ftp localhost
Trying 127.0.0.1…
Connected to localhost (127.0.0.1).
220 (vsFTPd 2.2.2)
Name (localhost:root): anonymous
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls
227 Entering Passive Mode (127,0,0,1,170,125).
150 Here comes the directory listing.
drwxr-xr-x    2 0        0            4096 Aug 30 15:37 pub
-rw-r–r–    1 0        0               0 Aug 30 15:39 test2
-rw-r–r–    1 0        0               0 Aug 30 15:38 testfile
226 Directory send OK.
ftp> get test2

The same test executed as root ( a local user) should fail as seen below.

# ftp localhost
Trying 127.0.0.1…
Connected to localhost (127.0.0.1).
220 (vsFTPd 2.2.2)
Name (localhost:root): root
530 This FTP server is anonymous only.
Login failed.
ftp>

Unix File Permissions and SELinux

One of the things that can ruin your day when it comes to getting and ftp server up and running is SELinux. However when setting up an anonymous download ftp server using the default ftp root directory you don’t actually need to change anything.

By default your ftp root directory is going to be /var/ftp/, and its SELinux context and default perms are going to be as seen below.

drwxr-xr-x. root root system_u:object_r:public_content_t:s0 /var/ftp

Here the default context is public_content_t which by allows reads but not writes, and the default Unix perms allow reads and not writes.

Changing Default FTP Root Directory

If you wanted to change anonymous vsftp to use a different root directory (other than /var/ftp) you would need to add the following line to /etc/vsftpd/vsftpd.conf. In the example below I am setting my new ftp root to /shared/ftp

anon_root=/shared/ftp

You are also going to need to asign the correct SELinux file context (public_content_t) to your new directory.

# semanage fcontext -a -t public_content_t “/shared/ftp(/.*)?”

# restorecon -vvFR /shared/ftp

Configuration Differences Between Anon Upload and Download

So as I stated above its actually a bit easier to configure an anonymous download only ftp server, than it is to configure it to allow uploads as well.  This section for reference only, my post on configuring anonymous upload and download ftp server can be reference here.

First you will need to assign a different SELinux context. Its public_content_rw_t not public_content_t.

# semanage fcontext -a -t public_content_rw_t ‘/var/ftp(/.*)’

# restorecon -vvFR /var/ftp

You will also need to fiddle with SELinux booleans

# setsebool -P allow_ftpd_anon_write=1

And we are also going to want to change the Unix permissions on our ftp root directory. Here we are changing group ownership to ftp and setting the setgid bit.

# chgrp ftp /var/ftp/
# chmod 2760 /var/ftp

Good luck and try not to break anything.

Advertisements

RHEL6 – How to Setup an Anonymous FTP Server


tow-truck-driver-cartoon-character-final-coghillToday on the fatmin we are going to setup an ftp server on RHEL6 that accepts anonymous uploads. We are going to do so with SELinux support and will be making modifications to iptables as well. Sounds fun, right?

Installation:

First and formost we need to install vsftpd

# yum -y install vsftpd && service vsftpd start && chkconfig vsftpd on

Our anonymous upload directory will be /var/ftp/anon, and we need to change group ownership to the ftp group and then change permissions so that the members of that group can write to it. Note that no one other than root can read or execute anything under /var/ftp/anon.

# chgrp ftp /var/ftp/anon
# chmod 730 /var/ftp/anon
# ls -ld /var/ftp/anon
drwx-wx—. 3 root ftp 4096 Oct 19 13:34 /v1

SELinux Support:

Next we need to configure SELinux support and assign the correct context to the /v1 directory and its future contents. Note -a is add -t is type.

# semanage fcontext -a -t public_content_rw_t ‘/var/ftp/anon(/.*)’

Now lets go ahead and apply the new context. Note -vv is verbose, -F force and R is recursive

# restorecon -vvFR /var/ftp/anon

Now we need to get and set the allow_ftpd_anon_write boolean

# setsebool -P allow_ftpd_anon_write=1

Now lets check to make sure the setting “stuck”.

# getsebool -a | grep allow_ftpd_anon_write
allow_ftpd_anon_write –> on

Configure Vsftpd:

Now vi /etc/vsftpd/vsftpd.conf and ensure that the following configuration values are set and un-commented. Note that I had to add the last line to my config file.

anonymous_enable=YES

anon_upload_enable=YES

chown_uploads=YES

chown_username=daemon

anon_umask=077

Configure iptables:

Add the following to /etc/sysconfig/iptables-config. In my case I only needed to add the ip_nat_ftp part to the line

IPTABLES_MODULES=”nf_conntrack_ftp ip_nat_ftp”

Now you are going to want to make sure that these two lines exist in /etc/sysconfig/iptables.

-A INPUT -m state –state ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p tcp –dport 21 -j ACCEPT

Now restart iptables

Addendum:

Note that I ran into issues with the semanage command below.

# semanage fcontext -a -t public_content_rw_t ‘/var/ftp/anon(/.*)’

It seems that the context assigned to the /var/ftp/anon directory was not changing correctly from public_content_t to public_content_rw_t.

# ls -Zd /var/ftp
drwxrwxrwx. root root system_u:object_r:public_content_t:s0 /var/ftp

However when I checked the file_contexts file all looked correct.

# cat /etc/selinux/targeted/contexts/files/file_contexts.local/var/ftp/anon(/.*)    system_u:object_r:public_content_rw_t:s0

So I ran the chon command seen below and did not run the restorecon command. This worked as afterwards the context on the directory /var/ftp/anon was correct.

# chcon -R -t public_content_rw_t /var/ftp/anon

 

RHEL6 – Managing SELinux Booleans

BooitemThis is my second post on SELinux. In case you missed the first one you can read it here. Today we are going to specifically discuss SELinux booleans

According to fedoraproject.org ,"SELinux booleans enable runtime customization of the SELinux policy. SELinux policy in Fedora has several booleans that allow you to quickly toggle a particular change in the policy." However i think its easier to explain them as SELinux configurations and settings that can be easily toggled on or toggled off.

The command getsebool -a is used to display available booleans, while setsebool is used to modify them. Using setsebool with the -P options makes that modification persistent across reboots.

To display a detailed list or booleans with descriptions run semanage boolean -l

Some common SELinux booleans are below.

ftp_home_dir   -> off   Allow ftp to read and write files in the user home directories

httpd_enable_cgi     -> on    Allow httpd cgi support

sftpd_anon_write      -> off   Allow anon internal-sftp to upload files, used for public file transfer services. Directories must be labeled public_content_rw_t.

allow_ftpd_anon_write   -> off   Allow ftp servers to upload files,  used for public file transfer services. Directories must be labeled public_content_rw_t.