Secure CVS Pserver Mini-HOWTO
Morgon Kanter
<morgon AT surgo DOT net>
Copyright © 2003 Morgon Kanter
February 2003
Revision History
Revision 1.1 2003-03-21 Revised by: mk
Fixed a missing link and added a section on CVSGrab
Revision 1.0 2003-02-01 Revised by: mk
Initial Release, reviewed by LDP.
This document will help you set up a more secure CVS Pserver for anonymous
CVS access.
Permission is granted to copy, distribute, and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or any
later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the
license is included in Section 6, entitled "GNU Free Documentation License".
-----------------------------------------------------------------------------
Table of Contents
1. Introduction
2. Getting the tools
2.1. What you need
2.2. Compiling the tools
3. Setting up the tools
3.1. Creating the CVS Repository
3.2. Setting up the jail
3.3. Adding anonymous access
3.4. Not quite done yet! Changing lock file locations
4. Alternatives to the Pserver
4.1. Access for developers
4.2. Anonymous CVS access by http
4.3. CVSGrab
5. Acknowledgements
6. GNU Free Documentation License
1. Introduction
CVS Pserver is, by definition, an insecure protocol. Among other things,
passwords are transmitted in plain text, making it undesirable for much use.
However, CVS Pserver is very good for providing anonymous CVS access to a
repository.
In this document we will introduce you to setting up a CVS repository
(although not intruding on the CVS HOWTO's space), and how to set up a chroot
jail for the Pserver. We will also talk about using SSH for developer access
to a repository.
-----------------------------------------------------------------------------
2. Getting the tools
2.1. What you need
You'll need the following things in order to set up a secure Pserver:
CVS
Of course, you will need to have CVS in order to be running it. You can
get it [http://www.cvshome.org] here.
cvsd
cvsd is a program that will run the CVS Pserver in a chroot jail. You
can get it [http://tiefighter.et.tudelft.nl/~arthur/cvsd/] here.
SSHd
If you want your developers to have secure access to the repository,
you'll have to be running an SSH server. However, setting up that access
is beyond the scope of this Mini-HOWTO. More information can be found at
[http://www.tldp.org/HOWTO/CVS-RCS-HOWTO.html] the CVS-RCS howto.
-----------------------------------------------------------------------------
2.2. Compiling the tools
If you are compiling from the sources, follow these instructions. If you
downloaded binaries, skip ahead to Section 2.2.2.
-----------------------------------------------------------------------------
2.2.1. Compiling CVS
After you have downloaded the CVS sources, unpack them into a directory and
cd into it. The default prefix is /usr/local; we've changed it to /usr for
this example. You might want to change mandir to wherever your man pages
reside (the default is PREFIX/man).
$ ./configure --prefix=/usr
$ make
# make install
-----------------------------------------------------------------------------
2.2.2. Compiling cvsd
There are a few configure switches you should be aware of here. The default
prefix is /usr/local, which in this document we are changing to /usr. You
should also change sysconfdir to /etc, where the system config files usually
reside. You might want to change mandir to wherever your manual pages reside
as well.
$ ./configure --prefix=/usr --sysconfdir=/etc
$ make
# make install
Now lets go on to setting up these wonderful tools.
-----------------------------------------------------------------------------
3. Setting up the tools
Now that CVS and cvsd are built, let's set them up.
-----------------------------------------------------------------------------
3.1. Creating the CVS Repository
Before we begin, I strongly recommend you read the CVS manual that was
installed with the rest of CVS. If the stand-alone info browser or the
texinfo package is installed on your system, you can see this manual by
typing the command info cvs at your shell.
First, plan out where you want your repository. Debian defaults to /var/lib
/cvs. My repository is under the directory /cvs/root, and is on its own small
partition. What you do depends on your needs and can vary widely.
Important Make sure that the repository is a subdirectory of an empty
directory! For example, if you are installing it into /var/lib/cvs,
put the repository in /var/lib/cvs/root (or whatever you want for
the last directory). This is because we create a chroot jail for
the Pserver!
After you have planned where you want to put your repository, made the
necessary partitions, if desired, and run the following command (we assume
that it will be at /cvs/root):
$ cvs -d /cvs/root init
That will initialize your repository and set up the necessary CVSROOT
files.
-----------------------------------------------------------------------------
3.2. Setting up the jail
Now that we have the CVSROOT set up, we need to copy the appropriate
libraries and files for cvsd, which runs the Pserver in the chroot jail.
-----------------------------------------------------------------------------
3.2.1. Transferring the necessary files
Note If you installed cvsd from a package management system like RPM, this
may already be done for you. If that is the case, skip ahead to the next
step.
Change your directory to /cvs (or whatever the directory before your root is)
and enter the following commands:
$ cvsd-buildroot /cvs
$ mkdir -p var/lock
$ adduser cvsd
$ addgroup cvsd
Thankfully, cvsd comes with the script cvsd-buildroot, so we don't have to
do all the necessary copying by hand. However, you should edit the /cvs/etc/
passwd file, and remove the entry for "root," as it's unneeded.
-----------------------------------------------------------------------------
3.2.2. Configuring cvsd
The defaults in /etc/cvsd/cvsd.conf are okay, but can be less than
desirable. Make sure that RootJail is set to wherever the chroot jail you
built is, and the repository is the directory where the repository is
relative to the chroot jail. Set maxconnections to whatever you desire, and
make sure that Uid and Gid are set to cvsd. If you are lacking an
already-built cvsd.conf file, here is mine:
Example 1. My cvsd.conf
Uid cvsd
Gid cvsd
PidFile /var/run/cvsd.pid
RootJail /cvs
MaxConnections 10
Nice 1
Listen * 2401
Repos /root
Limit coredumpsize 0
-----------------------------------------------------------------------------
3.3. Adding anonymous access
It's back to configuring CVS, but don't worry, we are almost there! We have
to edit a couple of necessary files to allow for anonymous access. First,
making sure you aren't in the CVS directory, check out the CVSROOT module:
# cvs -d /cvs/root checkout CVSROOT
# cd CVSROOT
Now edit the file READERS. Create it if it isn't there, and add a line that
reads "anonymous".
Important You NEED to have an extra line at the end of the file!
The file READERS is a list of users who have read-only access to the CVS
repository. People with write access are listed in the file WRITERS. Read the
cvs manual [1] for more information on these files.
Now commit the repository with the command below. We assume that your
current working directory is CVSROOT. If it isn't, forget the cd step.
# cd ../
# cvs -d /cvs/root commit
You should now get a message that says something like Re-building
administrative files, which means that it was successful.
One last step and we're all done! Run the following command, and when
prompted for a password, just press ENTER:
# cvsd-passwd /cvs/root anonymous
Congratulations! You now have secure, anonymous CVS Pserver access to the
repository!
-----------------------------------------------------------------------------
3.4. Not quite done yet! Changing lock file locations
There is one small feature here that is really beyond the scope of this
Mini-HOWTO but is worth noting nonetheless. It is the ability to change the
directory where the Pserver will place lock files.
Normally the Pserver will place lock files in the same directory as the
files that you are trying to check out, but this can cause permissions
mayhem. Step back to when we built the chroot jail for cvsd; we also created
the directory var/lock. This is where we will place the lockfiles instead.
So use the following example, replacing /cvs with wherever your chroot
environment is, and var with wherever the locks are going to be placed. Mine
are placed in var/lock, and there is nothing else under var, so a chown -R is
safe. Also, replace the cvsd user and group ids with the user and group ids
that cvsd runs as.
# cd /cvs
# chown -R cvsd:cvsd var
# chmod -R 775 var
# cd
# cvs -d /cvs/root checkout CVSROOT
# cd CVSROOT
Now we want to edit the file config. Change lock dir to the directory you
want the locks to be placed, in our case /var/lock.
Important Note that this applies to the Pserver AS WELL AS THE NON-CHROOT SSH
LOGIN METHOD! Ensure that this directory is not only in existence,
but that you can write to it as well, relative to your root
directory. This is why I have chosen /var/lock, because it
satisfies those conditions.
Now commit the changes:
# cd ../
# cvs -d /cvs/root commit
And that's it!
-----------------------------------------------------------------------------
4. Alternatives to the Pserver
4.1. Access for developers
Pserver is not a very good method to implement for your fellow developers
to access the repository. You can use CVS's SSH and ext method. Simply add
the user to the server's list of users, add the user to the file WRITERS, and
then they can do the following:
$ export CVS_RSH='/usr/bin/ssh'
$ cvs -d :ext:username@server.hostname:/cvs/root login
This is a much more secure way for developers to access the repository.
-----------------------------------------------------------------------------
4.2. Anonymous CVS access by http
There is another way to allow anonymous access to CVS. If there is an http
server and Python installed on the server, you can use a set of Python CGI
scripts called [http://viewcvs.sourceforge.net] viewcvs, which allow people
to view the CVS repository over the web, and can generate tarballs for users
to download.
There is also a set of Perl CGI scripts that do the same thing called
[http://stud.fh-heilbronn.de/~zeller/cgi/cvsweb.cgi/] cvsweb, but Viewcvs
is more mature and is preferred (at least by me).
-----------------------------------------------------------------------------
4.3. CVSGrab
[http://cvsgrab.sourceforge.net] CVSGrab is an end-user tool for
downloading the CVS repository by a ViewCVS interface. It is very useful when
you are behind a corporate firewall that blocks the Pserver, as you can just
grab the repository over standard HTTP. The only problem is if it doesn't
have a ViewCVS interface, but most free software repositories are now on the
web, and the few that still use cvsweb seem to be switching over to ViewCVS.
CVSGrab is written in Java, which may at first be a turn-off to some people
(it is to me), but it seems completely compilable using GCJ, the Java
front-end to GCC.
CVSGrab is a tool that goes hand-in-hand with ViewCVS. It is an end-user
tool, not one that you as a system administrator or repository administrator
would set up and configure.
-----------------------------------------------------------------------------
5. Acknowledgements
This Mini-HOWTO was written by Morgon Kanter, who is reachable at <morgon
AT surgo DOT net>, public key available from [http://www.surgo.net/
pubkey.asc] http://www.surgo.net/pubkey.asc. Email all problems with this
document to him, and they will be fixed ASAP.
My thanks goes out to all the people who contributed to CVS over the years,
as well as the creators of Viewcvs, and in turn the creators of cvsweb who
inspired it.
I would also like to thank Tabatha Persad for reviewing and helping me edit
this monster, as well as putting up with me. Thanks!
Also thanks to the various email contributors who pointed out missing
stuff. Thank you Y Giridhar Appaji Nag and Pasi Hirvonen!
-----------------------------------------------------------------------------
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Notes
[1] info cvs, if you have the stand-alone info viewer installed on your
system
