pam_mount - A PAM module that can mount volumes for a user session

This module is aimed at environments with SMB (Samba or Windows NT) or NCP (Netware or Mars-NWE) servers that Unix users wish to access transparently. It facilitates access to private volumes of these types well. The module also supports mounting home directories using loopback encrypted filesystems. The module was originally written for use on the GNU/Linux operating system but has since been modified to work on several flavors of BSD.

o Every user can access his own volumes

o The user needs to type the password just once (at login)

o The mounting process is transparent to the users

o There is no need to keep the login passwords in any additional file

o The volumes are unmounted upon logout, so it saves system resources, avoiding the need of listing every every possibly useful remote volume in /etc/fstab or in an automount/supermount config file. This is also necessary for securing encrypted filesystems.

Pam_mount "understands" SMB, NCP, and any type of filesystem that can be mounted using the standard mount command. If someone has a particular need for a different filesystem, feel free to ask me to include it and send me patches.

If you intend to use pam_mount to protect volumes on your computer using an encrypted filesystem system, please know that there are many other issues you need to consider in order to protect your data. For example, you probably want to disable or encrypt your swap partition (the

cryptoswap can help you do this). Don't assume a system is secure without carefully considering potential threats.

The primary configuration file for the pam_mount module is pam_mount.conf. On most platforms this file is read from /etc/security/pam_mount.conf. On OpenBSD pam_mount reads its configuration file from /etc/pam_mount.conf. Pam_mount.conf contains many comments documenting its use.

In addition, you must include two entries in the system's applicable /etc/pam.d/SERVICE config files, as the following example shows:

auth required pam_securetty.so auth required pam_pwdb.so shadow nullok auth required pam_nologin.so +++ auth optional pam_mount.so use_first_pass account required pam_pwdb.so password required pam_cracklib.so password required pam_pwdb.so shadow nullok use_authtok session required pam_pwdb.so session optional pam_console.so +++ session optional pam_mount.so

If you use pam_ldap, pam_winbind, or any other authentication services that make use of PAM's sufficient keyword then model your configuration on the following:

account sufficient pam_ldap.so auth required pam_mount.so auth sufficient pam_ldap.so use_first_pass auth required pam_unix.so use_first_pass session optional pam_mount.so

This allows the following:

1. Pam_mount will prompt for a password and export it to the PAM system.

2. Pam_ldap will use the password from the PAM system to try and authenticate the user. If this succedes, the user will be authenticated. If it fails, pam_unix will try to authenticate.

3. Pam_unix will try to authenticate the user if pam_ldap fails. If pam_unix fails, then the authentication will be refused.

If your volume has a different password than your system account, then encrypt the password to the volume you wish mounted using your system password as the key and store it somewhere on your system's local filesystem. Pam_mount supports transparently decrypting this filesystem key, as long as the cipher used is supported by openssl. Given:

sk

system key, the key or password used to log into the system

fsk

filesystem key, the key that allows you to use the filesystem you wish pam_mount to mount for you

E and D

an openssl supported synchronous encryption/decryption algorithm

efsk

encrypted filesystem key, efsk = E_sk (fsk), stored somewhere on the local filesystem (ie: /home/user.key)

Pam_mount will read efsk from the local filesystem, perform fsk = D_sk (efsk) and use fsk to mount the filesystem. If you change your system password, simply regenerate efsk using efsk = E_sk (fsk). If you want to mount this volume by hand, use something like openssl enc -d -aes-256-ecb -in /home/user.key | mount -p0 /home/user. More information about this technique is included in pam_mount.conf.

A script named mkehd is provided with pam_mount to help create encrypted home directories. If you have an entry for a user using encrypted home directories in pam_mount.conf, mkehd will create necessary filesystem images and possibly encrypted filesystem keys.

Individual users may define additional volumes to mount if allowed by pam_mount.conf (usually ~/.pam_mount.conf). The volume keyword is the only valid keyword in these per-user configuration files. If the luserconf parameter is set in pam_mount.conf, allowing user-defined volume, then users may mount and unmount any volume they own at any mount point they own. On some filesystem configurations this may be a security flaw so user-defined volumes are not allowed by the example pam_mount.conf distributed with pam_mount.

In general, you will leave all the first (general) parameters as provided by default. You only have to provide the user/volume list in the end of the file, following the examples.

To ensure that your system and, possibly, the remote server are all properly configured, you should try to mount all or some of the volumes by hand, using the same commands and mount points provided in pam_mount.conf. This will save you a lot of grief, since it is more difficult to debug the mounting process via pam_mount.

If you can mount the volumes by hand but it is not happening via pam_mount, you may want to enable the "debug" option in pam_mount.conf to see what is happening.

Verify if the user owns the mount point and has sufficient permissions over that. pam_mount will verify this and will refuse to mount the remote volume if the user does not own that directory.

If pam_mount is having trouble unmounting volumes upon logging out, enable the debug variable and check the lsof variable in pam_mount.conf. This causes pam_mount to run lsof upon logging out and write lsof's output to the system's logs.

W. Michael Petullo <mike@flyn.org>