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!
-----------------------------------------------------------------------------

6. GNU Free Documentation License

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8. TRANSLATION                                                               
                                                                             
Translation is considered a kind of modification, so you may                 
distribute translations of the Document under the terms of section 4.        
Replacing Invariant Sections with translations requires special              
permission from their copyright holders, but you may include                 
translations of some or all Invariant Sections in addition to the            
original versions of these Invariant Sections.  You may include a            
translation of this License, and all the license notices in the              
Document, and any Warrany Disclaimers, provided that you also include        
the original English version of this License and the original versions       
of those notices and disclaimers.  In case of a disagreement between         
the translation and the original version of this License or a notice         
or disclaimer, the original version will prevail.                            
                                                                             
If a section in the Document is Entitled "Acknowledgements",                 
"Dedications", or "History", the requirement (section 4) to Preserve         
its Title (section 1) will typically require changing the actual             
title.                                                                       
                                                                             
                                                                             
9. TERMINATION                                                               
                                                                             
You may not copy, modify, sublicense, or distribute the Document except      
as expressly provided for under this License.  Any other attempt to          
copy, modify, sublicense or distribute the Document is void, and will        
automatically terminate your rights under this License.  However,            
parties who have received copies, or rights, from you under this             
License will not have their licenses terminated so long as such              
parties remain in full compliance.                                           
                                                                             
                                                                             
10. FUTURE REVISIONS OF THIS LICENSE                                         
                                                                             
The Free Software Foundation may publish new, revised versions               
of the GNU Free Documentation License from time to time.  Such new           
versions will be similar in spirit to the present version, but may           
differ in detail to address new problems or concerns.  See                   
http://www.gnu.org/copyleft/.                                                
                                                                             
Each version of the License is given a distinguishing version number.        
If the Document specifies that a particular numbered version of this         
License "or any later version" applies to it, you have the option of         
following the terms and conditions either of that specified version or       
of any later version that has been published (not as a draft) by the         
Free Software Foundation.  If the Document does not specify a version        
number of this License, you may choose any version ever published (not       
as a draft) by the Free Software Foundation.                                 
                                                                             
                                                                             
ADDENDUM: How to use this License for your documents                         
                                                                             
To use this License in a document you have written, include a copy of        
the License in the document and put the following copyright and              
license notices just after the title page:                                   
                                                                             
Copyright (c)  YEAR  YOUR NAME.                                              
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 the section entitled "GNU               
Free Documentation License".                                                 
                                                                             
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,      
replace the "with...Texts." line with this:                                  
                                                                             
with the Invariant Sections being LIST THEIR TITLES, with the                
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.      
                                                                             
If you have Invariant Sections without Cover Texts, or some other            
combination of the three, merge those two alternatives to suit the           
situation.                                                                   
                                                                             
If your document contains nontrivial examples of program code, we            
recommend releasing these examples in parallel under your choice of          
free software license, such as the GNU General Public License,               
to permit their use in free software.                                        
                                                                             

Notes

[1]  info cvs, if you have the stand-alone info viewer installed on your     
     system                                                                  
