                           pam-afs-session 2.5
                   (PAM module for AFS PAGs and tokens)

                Written by Russ Allbery <rra@stanford.edu>

  Copyright 2005, 2006, 2007, 2008, 2010, 2011 The Board of Trustees of
  the Leland Stanford Junior University.  This software is distributed
  under a BSD-style license.  See the LICENSE file, included in this
  distribution, for copyright and redistribution information.

BLURB

  pam-afs-session is a PAM module intended for use with a Kerberos v5 PAM
  module to obtain an AFS PAG and AFS tokens on login.  It puts every new
  session in a PAG regardless of whether it was authenticated with
  Kerberos and either uses Heimdal's libkafs or runs a configurable
  external program to obtain tokens.  It supports using Heimdal's libkafs
  or OpenAFS's libkopenafs for the AFS interface and falls back to an
  internal implementation if libkafs isn't available.

DESCRIPTION

  pam-afs-session is a PAM module that isolates each login in a separate
  AFS PAG (so that they will not trample on each other's AFS tokens) and
  supports either running an external program to obtain AFS tokens from a
  Kerberos v5 ticket cache or using Heimdal's libkafs library.  It does
  not obtain tickets itself and must be used in conjunction with a
  Kerberos v5 PAM module to obtain tokens (setting up PAGs can be done
  without any Kerberos implementations).  It provides only the setcred and
  session PAM functions.

  There are two ways this module can obtain tokens:

   * If you have Heimdal's libkafs library available, the module can call
     libkafs's krb5_afslog function to obtain tokens directly.  If you are
     using Heimdal and obtaining tokens from Kerberos tickets, this is the
     recommended configuration, since it means the PAM module doesn't have
     to fork an external process.  If built with Heimdal's libkafs, this
     will be the default unless program is set in the module
     configuration.

   * Otherwise, the module will run an arbitrary external program to
     obtain tokens.  This is the most flexible option, works with MIT
     Kerberos in conjunction with the aklog program from OpenAFS or the
     afslog program from Heimdal, and can support programs that obtain AFS
     tokens via some means other than a Kerberos ticket cache created on
     login.

  For the AFS system call layer, pam-afs-session supports linking with the
  Heimdal libkafs library or OpenAFS's libkopenafs library.  As a
  fallback, and to support a low-dependency build, it also comes with a
  simple AFS system call implementation for Linux, Mac OS X, Solaris, or
  platforms that use syscall to call AFS functions.  It can also link with
  the older OpenAFS libraries when libkopenafs isn't available.

  The module can optionally be linked with Kerberos libraries to obtain
  configuration information from krb5.conf, to support the kdestroy
  option, and to use libkafs's functions for obtaining tokens.

  This module does not support getting tokens for the rmtsys AFS network
  redirection interface (generally used with the NFS translator).

  pam-afs-session is primarily tested on Linux.  I rely on reports from
  users to ensure it continues working on other platforms.  Please let me
  know if any problems you run into.

REQUIREMENTS

  The PAM implementations on Linux, Solaris, Mac OS X, HP-UX, and AIX are
  supported, although the module is primarily tested on Linux and only
  lightly tested (and not at all by me personally) on the other platforms.
  Use on platforms with other PAM implementations, such as IRIX or the
  *BSDs, will require more porting and will not currently work.  Patches
  are welcome.

  The module is written in C and should hopefully build on any system with
  an adequate PAM library that Libtool supports.

  Either Heimdal's libkafs or OpenAFS's libkopenafs are the preferred ways
  of making AFS system calls.  If neither are present during compile time,
  pam-afs-session will attempt to fall back on a built-in AFS system call
  layer.  To use the built-in AFS system call interface on Linux, Mac OS
  X, and Solaris 11, the system must run a new enough version of OpenAFS
  or Arla to support AFS system calls through ioctl on a file in /proc or
  /dev.  On other systems with a simple system call interface, configure
  must be able to find the AFS header afs/param.h in order to get the
  system call numbers for that platform.  On AIX and IRIX, configure will
  attempt to locate the necessary OpenAFS libraries for lsetpag (either
  libafsauthent or libsys) but will not support deleting tokens at the end
  of a session.

  The module can optionally use Heimdal's libkafs library to obtain tokens
  as well as create the PAG.  If you are using Heimdal and obtaining
  tokens from Kerberos tickets, this is the recommended configuration,
  since it means that the PAM module doesn't have to fork an external
  process.  For other users, an external aklog program that obtains tokens
  is necessary (and not provided by this module).

  To obtain configuration information from krb5.conf and to support the
  kdestroy option, either MIT Kerberos or Heimdal are required.

  Testing the module requires a system with AFS installed and working so
  that the PAG creation and manipulation can be tested.  Running the
  complete test suite also requires that you have an existing ticket cache
  and working aklog program.  Those portions of the test suite will be
  skipped if AFS or a Kerberos ticket cache do not appear to be available.

  To run the POD test suite, you must have the Perl 5.006 or later and the
  modules Test::More and Test::Pod installed.  Test::More comes with Perl
  5.8 or later.  Test::Pod is available from CPAN and currently must be
  installed separately, but the POD tests will be skipped without
  interfering with the rest of the tests if it's not installed.

  To check spelling in the POD documentation, Pod::Spell (available from
  CPAN) and either aspell or ispell with the american dictionary are also
  required.  The user's path is searched for aspell or ispell and aspell
  is preferred.  Spelling tests are disabled by default since spelling
  dictionaries differ too much between systems.  To enable those tests,
  set RRA_MAINTAINER_TESTS to a true value.

  To bootstrap from a Git checkout, or if you change the Automake files
  and need to regenerate Makefile.in, you will need Automake 1.11 or
  later.  For bootstrap or if you change configure.ac or any of the m4
  files it includes and need to regenerate configure or config.h.in, you
  will need Autoconf 2.64 or later.  Perl is also required to generate the
  manual pages from a fresh Git checkout.

COMPILING AND INSTALLING

  To build the module, just run:

      ./configure
      make

  Kerberos support is enabled by default if configure can find Kerberos
  libraries.  If your Kerberos libraries aren't installed in a location
  found by your compiler by default and krb5-config isn't on your PATH,
  use the --with-krb5=PATH option to configure.  The Kerberos libraries
  will then be expected in PATH/lib and the headers in PATH/include.

  To specify a particular krb5-config script to use, either set the
  KRB5_CONFIG environment variable or pass it to configure like:

      ./configure KRB5_CONFIG=/path/to/krb5-config

  To not use krb5-config and force library probing even if there is a
  krb5-config script on your path, set KRB5_CONFIG to a nonexistent path:

      ./configure KRB5_CONFIG=/nonexistent

  To disable Kerberos support, even if you have Kerberos libraries
  available, pass --without-krb5 to configure.

  By default, the first aklog program found on the PATH will be compiled
  into the module as the default aklog program to run.  This can be
  overridden by the program PAM option.  To specify an explicit path to
  aklog, use:

      ./configure --with-aklog=/path/to/aklog

  instead.

  To install the module into /usr/local/lib/security and the man page into
  /usr/local/share/man/man5, run:

      make install

  You can change the installation locations with the --prefix, --mandir,
  and --libdir options to configure.  The module will normally be
  installed in a subdirectory of $libdir named security, but if --prefix
  is set to /usr (rather than /usr/local, the default), the module will be
  installed in /lib/security (or /lib32/security or /lib64/security if
  they exist) to match the default PAM configuration.  Alternately, you
  can simply copy pam_afs_session.so to whatever directory you use for PAM
  modules.  On Solaris, you will need to make the module executable.

  By default, if libkafs or libkopenafs are available, pam-afs-session
  will use them in preference to its own system call implementation.  If
  for some reason you want to build pam-afs-session without a dependency
  on those libraries even though you have them installed, pass the
  --without-libkafs flag to configure.

  If you are building this module without libkafs on a platform other than
  Linux, configure needs to find the AFS header afs/param.h.  If this is
  not in the normal include path, pass the --with-afs-headers option to
  configure to point the compiler at the correct path.  For example, if
  your AFS headers are in /usr/afsws/include, run:

      ./configure --with-afs-headers=/usr/afsws/include

  instead.

  You can pass the --enable-reduced-depends flag to configure to try to
  minimize the shared library dependencies encoded in the binaries.  This
  omits from the link line all the libraries included solely because
  libkafs or the Kerberos libraries depend on them and instead links the
  programs only against libraries whose APIs are called directly.  This
  will only work with shared libraries and will only work on platforms
  where shared libraries properly encode their own dependencies (such as
  Linux).  It is intended primarily for building packages for Linux
  distributions to avoid encoding unnecessary shared library dependencies
  that make shared library migrations more difficult.  If none of the
  above made any sense to you, don't bother with this flag.

TESTING

  pam-afs-session comes with a test suite, which you can run after
  building pam-afs-session with:

      make check

  If a test case fails, please run the that individual test case with
  verbose output using:

      tests/runtests -o <name-of-test>

  and send me the output when reporting the problem.

CONFIGURING

  Just installing the module does not enable it or change anything about
  your system authentication configuration.  You have to add the module to
  your PAM configuration, generally in the session group and possibly in
  the auth group as well.  See the platform-specific instructions below.

  On all platforms, options can be put after the module name in the PAM
  configuration file.  This is useful if you don't have Kerberos libraries
  available or if you want different configurations for different
  services.

  If Kerberos support was enabled, configuration options may also be put
  in the krb5.conf file used by your Kerberos libraries (usually
  /etc/krb5.conf or /usr/local/etc/krb5.conf) instead or in addition to
  the PAM configuration.  See the man page for more details.  This is
  recommended for general system configuration, since the krb5.conf
  configuration syntax is a little nicer and more flexible.

  See the files in the examples directory for examples of PAM
  configuration for various operating systems.  Contributions for
  additional operating systems are welcome.

 Linux

  To use it in conjunction with pam_krb5 on a Debian system, put something
  like:

      auth [success=ok default=1] pam_krb5.so
      auth [default=done]         pam_afs_session.so program=/usr/bin/aklog
      auth required               pam_unix.so try_first_pass nullok_secure

  in /etc/pam.d/common-auth and something like:

      session optional pam_krb5.so
      session required pam_afs_session.so program=/usr/bin/aklog

  in /etc/pam.d/common-session.  The program= setting is optional if
  /usr/bin/aklog was in your path when the module was compiled or was
  specified via the --with-aklog option to configure.

  You may want to stack your Kerberos v5 PAM module and the Unix module
  differently, but note that this module should always run after the
  Kerberos v5 PAM module.  If there is no ticket cache available in the
  PAM environment, it will succeed silently.

  On Red Hat systems, modify /etc/pam.d/system-auth instead; it contains
  all of the configuration for the different stacks.

  Be aware that the pam_keyinit module can have a bad interaction with
  this module.  pam_keyinit initializes a new kernel keyring and will
  remove the keyring created by pam_afs_session to represent your PAG and
  hold your tokens.  pam_afs_session will attempt to detect this and add
  the PAG and tokens back, but to do so it must run after pam_keyinit in
  the session stack.  To be safe, you may want to remove this PAM module
  unless you're using it.

  Note that this is not an authentication module and will always return
  PAM_SUCCESS to any authentication attempt, so never make this module
  sufficient in your authentication stack.  It's only listed as an auth
  module because it provides a pam_setcred implementation and some
  programs need to call pam_setcred rather than pam_open_session (screen
  savers, for instance, to refresh credentials).

 Solaris

  Solaris doesn't support the [] keywords that Linux PAM does, so if you
  want to mark the Kerberos v5 PAM module as sufficient and fall back on
  the Unix module only if it fails, you won't be able to easily run
  pam_afs_session in the auth group.  For most applications, this isn't a
  problem; running pam_afs_session only from the session group with
  something like:

      other session required /usr/local/lib/security/pam_afs_session.so 
          minimum_uid=100 retain_after_close

  (all on one line) in /etc/pam.conf will be sufficient.  Make sure this
  line is after the Kerberos v5 PAM module's session call.

  However, note that login and dtlogin, at least under Solaris 10,
  apparently call pam_open_session before pam_setcred, and the
  open_session function of the native Kerberos v5 PAM module doesn't set
  up the ticket cache.  This means that calling pam_afs_session only in
  the session group won't work, since it will be called before the setcred
  function of the Kerberos v5 PAM module and hence won't have a ticket
  cache available yet.  There are two possible solutions: replace the
  native Kerberos v5 PAM module with another module, such as:

      http://www.eyrie.org/~eagle/software/pam-krb5/

  that does the same thing in open_session as in setcred, or also call
  pam_afs_session from the auth group:

      login auth required /usr/local/lib/security/pam_afs_session.so
          minimum_uid=100

  after the Kerberos v5 PAM module (and likewise for dtlogin).  This means
  that you cannot use sufficient in the auth group for the Kerberos v5 PAM
  module, since that will then abort the group before pam_afs_session
  runs.

  See the man page for pam.conf on Solaris for more configuration
  information.

 HP-UX

  HP-UX configuration is very similar to Solaris.  Something like:

      dtaction session required /usr/lib/security/pam_afs_session.so
      dtlogin  session required /usr/lib/security/pam_afs_session.so
      login    session required /usr/lib/security/pam_afs_session.so
      OTHER    session required /usr/lib/security/pam_afs_session.so

  will use pam-afs-session for most login sessions.

 Mac OS X

  For Mac OS X, PAM isn't used for system login and is therefore mostly
  useful for remote ssh.  To use this module with sshd, add it to the
  session group of the sshd PAM configuration, and it will then obtain
  tokens with forwarded tickets via GSS-API or tickets obtained via
  KerberosAuthentication.

  Note that PAGs are not supported on Mac OS X, so you will need to add
  the "nopag" parameter to the PAM configuration for this module.  Note
  also that while the latest Mac OS X ssh daemon supports GSS-API
  authentication, it apparently doesn't make the forwarded tickets
  available to the PAM stack, so pam-afs-session cannot properly set up
  tokens during GSS-API login.

IMPLEMENTATION NOTES

  pam-afs-session supports three basic usage patterns: creating a new
  session using either pam_open_session or pam_setcred(PAM_ESTABLISH_CRED)
  (or both), closing a session with pam_close_session or
  pam_setcred(PAM_DELETE_CRED), and refreshing credentials with
  pam_setcred(PAM_REINITIALIZE_CRED).  In general, the same behavior
  occurs whether using the pam_*_session interface or the pam_setcred
  interface, since some PAM-using programs call one and some call the
  other.  In all cases, pam-afs-session will log an error and then
  successfully exit if AFS doesn't appear to be running (checked with the
  k_hasafs interface).

  pam-afs-session stores a PAM data key named "pam_afs_session" once it
  has successfully created a PAG and a token.  If this key is present in
  the PAM data when pam_open_session or pam_setcred with the
  PAM_ESTABLISH_CRED flag is called, it will successfully do nothing to
  keep from doing duplicate work.  Otherwise, it will always create a PAG
  and then will either call krb5_afslog or run an external program to
  obtain tokens provided that the environment variable KRB5CCNAME is set
  in the PAM environment.

  If libkafs was found and used at compile time and if krb5_afslog is
  available, the default is to run krb5_afslog to obtain tokens.
  Otherwise, the default is to run whatever aklog program was found at
  compile time.  If program is set explicitly in the configuration,
  pam-afs-session will always run that program rather than calling
  krb5_afslog.

  When pam_close_session or pam_setcred(PAM_DELETE_CRED) is called,
  pam-afs-session will destroy the user's tokens only if the PAM data key
  "pam_afs_session" is present (meaning that pam-afs-session previously
  obtained tokens).  This check is present to avoid deleting tokens when
  session initialization failed, since in that case no new PAG may have
  been created and we may be deleting tokens that are not ours to delete.

  pam_setcred(PAM_REINITIALIZE_CRED) is treated similarly to the opening
  of a new session except that no PAG is created.  Instead, only the
  program to obtain tokens is run, provided that KRB5CCNAME is set in the
  PAM environment.  This interface is used by programs such as screen
  savers and lockers to refresh a user's credentials.

  pam-afs-session requires that the user (obtained via pam_get_user)
  exists in the local passwd file or equivalent (using getpwnam).  If
  running an external program, the program is run under that user's UID
  and primary GID.  If calling krb5_afslog, that user's UID is used for
  the "AFS ID" field in the tokens display (which is entirely cosmetic).

HOMEPAGE AND SOURCE REPOSITORY

  The pam-afs-session web page at:

      http://www.eyrie.org/~eagle/software/pam-afs-session/

  will always have the current version of this package, the current
  documentation, and pointers to any additional resources.

  pam-afs-session is maintained using Git.  You can access the current
  source by cloning the repository at:

      git://git.eyrie.org/afs/pam-afs-session.git

  or view the repository via the web at:

      http://git.eyrie.org/?p=afs/pam-afs-session.git

THANKS

  Some of the ideas behind this PAM module (although not the code) are
  taken from the libpam-openafs-session Debian package written by Sam
  Hartman and the pam_afs2 module written by Douglas Engert.  Thanks to
  both of them for their previous work.  Any errors in this implementation
  are mine.

  The Linux system call layer was based on inspection of the code in
  OpenAFS and on discussions with Jeffrey Hutzelman on how best to
  implement an AFS system call layer and on how the pieces work.  I
  couldn't have written this code without his explanations.

  Thanks to Douglas Engert for an initial code review, for Solaris
  porting, for suggesting the always_aklog and aklog_homedir options, and
  for catching various other problems and missing features.

  Thanks to Sean O'Malley for additional Solaris porting information and
  for testing with the Sun C compiler.

  Thanks to Joe Buehler for porting and testing on HP-UX.

  Thanks to Markus Moeller for multiple patches and suggestions for
  improved portability for pam-krb5, from which this module has also
  benefitted.
