Home > Cvs Server > Setting up the server for password authentication

Setting up the server for password authentication

First of all, you probably want to tighten the permissions on the $CVSROOT and $CVSROOT/CVSROOT directories. See Password authentication security, for more details.

On the server side, the file /etc/inetd.conf needs to be edited so inetd knows to run the command cvs pserver when it receives a connection on the right port. By default, the port number is 2401; it would be different if your client were compiled with CVS_AUTH_PORT defined to something else, though. This can also be specified in the CVSROOT variable (see Remote repositories) or overridden with the CVS_CLIENT_PORT environment variable (see Environment variables).

If your inetd allows raw port numbers in /etc/inetd.conf, then the following (all on a single line in inetd.conf) should be sufficient:

     2401  stream  tcp  nowait  root  /usr/local/bin/cvs
     cvs -f --allow-root=/usr/cvsroot pserver

(You could also use the `-T‘ option to specify a temporary directory.)

The `–allow-root‘ option specifies the allowable cvsroot directory. Clients which attempt to use a different cvsroot directory will not be allowed to connect. If there is more than one cvsroot directory which you want to allow, repeat the option. (Unfortunately, many versions of inetd have very small limits on the number of arguments and/or the total length of the command. The usual solution to this problem is to have inetd run a shell script which then invokes cvs with the necessary arguments.)

If your inetd wants a symbolic service name instead of a raw port number, then put this in /etc/services:

     cvspserver      2401/tcp

and put cvspserver instead of 2401 in inetd.conf.

If your system uses xinetd instead of inetd, the procedure is slightly different. Create a file called /etc/xinetd.d/cvspserver containing the following:

     service cvspserver
     {
        port        = 2401
        socket_type = stream
        protocol    = tcp
        wait        = no
        user        = root
        passenv     = PATH
        server      = /usr/local/bin/cvs
        server_args = -f --allow-root=/usr/cvsroot pserver
     }

(If cvspserver is defined in /etc/services, you can omit the port line.)

Once the above is taken care of, restart your inetd, or do whatever is necessary to force it to reread its initialization files.

If you are having trouble setting this up, see Connection.

Because the client stores and transmits passwords in cleartext (almost—see Password authentication security, for details), a separate cvs password file is generally used, so people don’t compromise their regular passwords when they access the repository. This file is $CVSROOT/CVSROOT/passwd (see Intro administrative files). It uses a colon-separated format, similar to /etc/passwd on Unix systems, except that it has fewer fields: cvs username, optional password, and an optional system username for cvs to run as if authentication succeeds. Here is an example passwd file with five entries:

     anonymous:
     bach:ULtgRLXo7NRxs
     spwang:1sOp854gDF3DY
     melissa:tGX1fS8sun6rY:pubcvs
     qproj:XR4EZcEs0szik:pubcvs

(The passwords are encrypted according to the standard Unix crypt() function, so it is possible to paste in passwords directly from regular Unix /etc/passwd files.)

The first line in the example will grant access to any cvs client attempting to authenticate as user anonymous, no matter what password they use, including an empty password. (This is typical for sites granting anonymous read-only access; for information on how to do the “read-only” part, see Read-only access.)

The second and third lines will grant access to bach and spwang if they supply their respective plaintext passwords.

The fourth line will grant access to melissa, if she supplies the correct password, but her cvs operations will actually run on the server side under the system user pubcvs. Thus, there need not be any system user named melissa, but there must be one named pubcvs.

The fifth line shows that system user identities can be shared: any client who successfully authenticates as qproj will actually run as pubcvs, just as melissa does. That way you could create a single, shared system user for each project in your repository, and give each developer their own line in the $CVSROOT/CVSROOT/passwd file. The cvs username on each line would be different, but the system username would be the same. The reason to have different cvs usernames is that cvs will log their actions under those names: when melissa commits a change to a project, the checkin is recorded in the project’s history under the name melissa, not pubcvs. And the reason to have them share a system username is so that you can arrange permissions in the relevant area of the repository such that only that account has write-permission there.

If the system-user field is present, all password-authenticated cvs commands run as that user; if no system user is specified, cvs simply takes the cvs username as the system username and runs commands as that user. In either case, if there is no such user on the system, then the cvs operation will fail (regardless of whether the client supplied a valid password).

The password and system-user fields can both be omitted (and if the system-user field is omitted, then also omit the colon that would have separated it from the encrypted password). For example, this would be a valid $CVSROOT/CVSROOT/passwd file:

     anonymous::pubcvs
     fish:rKa5jzULzmhOo:kfogel
     sussman:1sOp854gDF3DY

When the password field is omitted or empty, then the client’s authentication attempt will succeed with any password, including the empty string. However, the colon after the cvs username is always necessary, even if the password is empty.

cvs can also fall back to use system authentication. When authenticating a password, the server first checks for the user in the $CVSROOT/CVSROOT/passwd file. If it finds the user, it will use that entry for authentication as described above. But if it does not find the user, or if the cvs passwd file does not exist, then the server can try to authenticate the username and password using the operating system’s user-lookup routines (this “fallback” behavior can be disabled by setting SystemAuth=no in the cvs config file, see config).

The default fallback behavior is to look in /etc/passwd for this system user unless your system has PAM (Pluggable Authentication Modules) and your cvs server executable was configured to use it at compile time (using ./configure --enable-pam – see the INSTALL file for more). In this case, PAM will be consulted instead. This means that cvs can be configured to use any password authentication source PAM can be configured to use (possibilities include a simple UNIX password, NIS, LDAP, and others) in its global configuration file (usually /etc/pam.conf or possibly /etc/pam.d/cvs). See your PAM documentation for more details on PAM configuration.

Note that PAM is an experimental feature in cvs and feedback is encouraged. Please send a mail to one of the cvs mailing lists (info-cvs@gnu.org or bug-cvs@gnu.org) if you use the cvs PAM support.

WARNING: Using PAM gives the system administrator much more flexibility about how cvs users are authenticated but no more security than other methods. See below for more.

CVS needs an “auth”, “account” and “session” module in the PAM configuration file. A typical PAM configuration would therefore have the following lines in /etc/pam.conf to emulate the standard cvs system /etc/passwd authentication:

     cvs	auth	    required	pam_unix.so
     cvs	account	    required	pam_unix.so
     cvs	session	    required	pam_unix.so

The the equivalent /etc/pam.d/cvs would contain

     auth	    required	pam_unix.so
     account	    required	pam_unix.so
     session	    required	pam_unix.so

Some systems require a full path to the module so that pam_unix.so (Linux) would become something like /usr/lib/security/$ISA/pam_unix.so.1 (Sun Solaris). See the contrib/pam subdirectory of the cvs source distribution for further example configurations.

The PAM service name given above as “cvs” is just the service name in the default configuration and can be set using ./configure --with-hardcoded-pam-service-name=<pam-service-name> before compiling. cvs can also be configured to use whatever name it is invoked as as its PAM service name using ./configure --without-hardcoded-pam-service-name, but this feature should not be used if you may not have control of the name cvs will be invoked as.

Be aware, also, that falling back to system authentication might be a security risk: cvs operations would then be authenticated with that user’s regular login password, and the password flies across the network in plaintext. See Password authentication security for more on this. This may be more of a problem with PAM authentication because it is likely that the source of the system password is some central authentication service like LDAP which is also used to authenticate other services.

On the other hand, PAM makes it very easy to change your password regularly. If they are given the option of a one-password system for all of their activities, users are often more willing to change their password on a regular basis.

In the non-PAM configuration where the password is stored in the CVSROOT/passwd file, it is difficult to change passwords on a regular basis since only administrative users (or in some cases processes that act as an administrative user) are typically given access to modify this file. Either there needs to be some hand-crafted web page or set-uid program to update the file, or the update needs to be done by submitting a request to an administrator to perform the duty by hand. In the first case, having to remember to update a separate password on a periodic basis can be difficult. In the second case, the manual nature of the change will typically mean that the password will not be changed unless it is absolutely necessary.

Note that PAM administrators should probably avoid configuring one-time-passwords (OTP) for cvs authentication/authorization. If OTPs are desired, the administrator may wish to encourage the use of one of the other Client/Server access methods. See the section on see Remote repositories for a list of other methods.

Right now, the only way to put a password in the cvs passwd file is to paste it there from somewhere else. Someday, there may be a cvs passwd command.

Unlike many of the files in $CVSROOT/CVSROOT, it is normal to edit the passwd file in-place, rather than via cvs. This is because of the possible security risks of having the passwd file checked out to people’s working copies. If you do want to include the passwd file in checkouts of $CVSROOT/CVSROOT, see checkoutlist

Advertisements
Categories: Cvs Server
  1. No comments yet.
  1. No trackbacks yet.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: