- Pluggable Authentication Module
- 認証処理を行うモジュール群とそれを利用するためのAPIからなるユーザー認証システム
- http://www.linux-pam.org/ のドキュメントでは認証処理を行うモジュールをLinux-PAM Module、APIを利用するアプリケーションをLinux-PAM Applicationと呼んでいる
Chapter 6. A reference guide for available modules
linuxでログインするとき/etc/passwdや/etc/shadowを見て認証を行う
/etc/security/time.confの記述に従って、時間帯によるログインの制限ができる
root以外のログインを禁止する
常に許可する
ログイン時に自動でマウントする 暗号化したホームディレクトリのマウントなどに使える
ldapによる認証を行う
- sudo
- login
- /etc/pam.d/*に各Applicationがどのようにモジュールを利用するかを記述したファイルが存在する
Linuxの各アプリケーションが共通して利用する「PAM認証」についてやhttps://www.freebsd.org/doc/en/articles/pam/pam-essentials.html が分かりやすい
% ls /etc/pam.d/
accountsservice cron newusers
chfn cups-daemon other
chpasswd gnome-screensaver passwd
chsh lightdm polkit-1
common-account lightdm-autologin ppp
common-auth lightdm-greeter samba
common-password lightdm-remote-freerdp su
common-session lightdm-remote-uccsconfigure sudo
common-session-noninteractive login
% cat /etc/pam.d/login
#
# The PAM configuration file for the Shadow `login' service
#
# Enforce a minimal delay in case of failure (in microseconds).
# (Replaces the `FAIL_DELAY' setting from login.defs)
# Note that other modules may require another minimal delay. (for example,
# to disable any delay, you should add the nodelay option to pam_unix)
auth optional pam_faildelay.so delay=3000000
# Outputs an issue file prior to each login prompt (Replaces the
# ISSUE_FILE option from login.defs). Uncomment for use
# auth required pam_issue.so issue=/etc/issue
# Disallows root logins except on tty's listed in /etc/securetty
# (Replaces the `CONSOLE' setting from login.defs)
#
# With the default control of this module:
# [success=ok new_authtok_reqd=ok ignore=ignore user_unknown=bad default=die]
# root will not be prompted for a password on insecure lines.
# if an invalid username is entered, a password is prompted (but login
# will eventually be rejected)
#
# You can change it to a "requisite" module if you think root may mis-type
# her login and should not be prompted for a password in that case. But
# this will leave the system as vulnerable to user enumeration attacks.
#
# You can change it to a "required" module if you think it permits to
# guess valid user names of your system (invalid user names are considered
# as possibly being root on insecure lines), but root passwords may be
# communicated over insecure lines.
auth [success=ok new_authtok_reqd=ok ignore=ignore user_unknown=bad default=die] pam_securetty.so
# Disallows other than root logins when /etc/nologin exists
# (Replaces the `NOLOGINS_FILE' option from login.defs)
auth requisite pam_nologin.so
# SELinux needs to be the first session rule. This ensures that any
# lingering context has been cleared. Without out this it is possible
# that a module could execute code in the wrong domain.
# When the module is present, "required" would be sufficient (When SELinux
# is disabled, this returns success.)
session [success=ok ignore=ignore module_unknown=ignore default=bad] pam_selinux.so close
# This module parses environment configuration file(s)
# and also allows you to use an extended config
# file /etc/security/pam_env.conf.
#
# parsing /etc/environment needs "readenv=1"
session required pam_env.so readenv=1
# locale variables are also kept into /etc/default/locale in etch
# reading this file *in addition to /etc/environment* does not hurt
session required pam_env.so readenv=1 envfile=/etc/default/locale
# Standard Un*x authentication.
@include common-auth
# This allows certain extra groups to be granted to a user
# based on things like time of day, tty, service, and user.
# Please edit /etc/security/group.conf to fit your needs
# (Replaces the `CONSOLE_GROUPS' option in login.defs)
auth optional pam_group.so
# Uncomment and edit /etc/security/time.conf if you need to set
# time restrainst on logins.
# (Replaces the `PORTTIME_CHECKS_ENAB' option from login.defs
# as well as /etc/porttime)
# account requisite pam_time.so
# Uncomment and edit /etc/security/access.conf if you need to
# set access limits.
# (Replaces /etc/login.access file)
# account required pam_access.so
# Sets up user limits according to /etc/security/limits.conf
# (Replaces the use of /etc/limits in old login)
session required pam_limits.so
# Prints the last login info upon succesful login
# (Replaces the `LASTLOG_ENAB' option from login.defs)
session optional pam_lastlog.so
# Prints the message of the day upon succesful login.
# (Replaces the `MOTD_FILE' option in login.defs)
# This includes a dynamically generated part from /run/motd.dynamic
# and a static (admin-editable) part from /etc/motd.
session optional pam_motd.so motd=/run/motd.dynamic noupdate
session optional pam_motd.so
# Prints the status of the user's mailbox upon succesful login
# (Replaces the `MAIL_CHECK_ENAB' option from login.defs).
#
# This also defines the MAIL environment variable
# However, userdel also needs MAIL_DIR and MAIL_FILE variables
# in /etc/login.defs to make sure that removing a user
# also removes the user's mail spool file.
# See comments in /etc/login.defs
session optional pam_mail.so standard
# Standard Un*x account and session
@include common-account
@include common-session
@include common-password
# SELinux needs to intervene at login time to ensure that the process
# starts in the proper default security context. Only sessions which are
# intended to run in the user's context should be run after this.
session [success=ok ignore=ignore module_unknown=ignore default=bad] pam_selinux.so open
# When the module is present, "required" would be sufficient (When SELinux
# is disabled, this returns success.)
- 認証の情報は
pam_handle_t
型(へのポインタ)のpamh
が持っている - Application側もModule側も
pam_set_item
やpam_get_item
で必要な情報をsetしたりgetしたりする struct pam_conv
にApplicationとModuleが直接やりとりするためのcallback関数を設定する
The Linux-PAM Module Writers' Guide
コードはlinux-pam.gitのmodules(特にpam_permitは単純)やSample PAM Moduleを参考にすればいいと思う
PAM_USERか、PAM_USERがNULLならプロンプトを出してユーザー名を取得する
The Linux-PAM Application Developers' Guide
Sample PAM Applicationやsudoのソースコードのplugins/sudoers/auth/pam.c、loginのソースコードのlogin.cが参考になると思う
sudoやloginのソースコードの取得はUbuntuならapt-get source sudo(またはlogin)
とすればいいはず
authentication token(パスワードとか)の変更
認証に成功したユーザーのセッションの開始時に呼び出す。pam_close_sessionをあとで呼び出すべきである。
セッション終了時に呼び出す。
パスワードの期限切れ、アカウントの期限切れなどを調べてユーザーアカウントが有効かどうかを判定する
It is typically called after the user has been authenticated.
It should be called to set the credentials after a user has been authenticated and before a session is opened for the user (with pam_open_session(3)).
ユーザーの認証
pam_authenticateが認証に失敗した時にアプリケーションに制御を返すまでの時間を設定する
初期化
第一引数service_nameが/etc/pam.d/<service_name>に対応する
エラーコードを説明する文字列
Application側API | Module側 |
---|---|
pam_authenticate | pam_sm_authenticate |
pam_setcred | pam_sm_setcred |
pam_acct_mgmt | pam_sm_acct_mgmt |
pam_open_session | pam_sm_open_session |
pam_close_session | pam_sm_close_session |
pam_chauthtok | pam_sm_chauthtok |
呼び出す順序は3.4. Transactionsが詳しい