Estoy intentando configurar una estructura de autenticación SSH, pero tengo problemas con /etc/ssh/sshd_config vs /etc/pam.d/sshd.
Requisitos:
- Cuentas con privilegios root/sudo
- requerir autenticación de clave pública, seguida inmediatamente por
- Autenticador de Google
- Cuentas sin privilegios
- Requiere sólo autenticación de clave pública.
En otras palabras, no se debe permitir la autenticación basada en contraseña y siempre se requiere la autenticación con clave pública, siendo requerido condicionalmente Google Authenticator.
Qué esta trabajando:
Las cuentas privilegiadas funcionan exactamente como necesito: clave pública seguida de Google Authenticator. También verifiqué que las claves públicas que faltan en ~/.ssh/authorized_keys se rechazan y verifiqué que se rechazan los intentos de inicio de sesión sin proporcionar ninguna clave.
Lo que no funciona:
Las cuentas sin privilegios parecen solicitar correctamente la contraseña para desbloquear la clave privada, y creo que la clave se logra. Pero la autenticación falla con el mensaje:
Permission denied (keyboard-interactive).
$ ssh -v -i id_rsa_unprivileged unprivileged@blahblah
debug1: Server accepts key: pkalg ssh-rsa blen 2071
Enter passphrase for key 'id_rsa_unprvileged':
Authenticated with partial success.
debug1: Authentications that can continue: keyboard-interactive
debug1: Next authentication method: keyboard-interactive
debug1: Authentications that can continue: keyboard-interactive
debug1: No more authentication methods to try.
unprivileged@blahblah: Permission denied (keyboard-interactive).
$ sudo cat /var/log/auth.log
Sep 3 00:44:13 hostname sshd[4249]: pam_succeed_if(sshd:auth): requirement "user ingroup 2faexempt" was met by user "unprivileged"
Sep 3 00:44:13 hostname sshd[4247]: error: PAM: Permission denied for unprivileged from IP ADDRESS
Sep 3 00:44:13 hostname sshd[4247]: Connection closed by IP ADDRESS port PORT [preauth]
Nota: Las cuentas sin privilegios rechazan correctamente las claves públicas que faltan en ~/.ssh/authorized_keys y rechazan los intentos de inicio de sesión que no proporcionan una clave.
Lo que hice:
MiestrategiaEra crear un grupo llamado "2faexempt" y agregar aquellas cuentas que deberían estar exentas de la autenticación de 2 factores (las cuentas sin privilegios). Luego edité /etc/ssh/sshd y /etc/pam.d/sshd para reflejar la política que necesito.
$ cat /etc/ssh/sshd_config
# $OpenBSD: sshd_config,v 1.100 2016/08/15 12:32:04 naddy Exp $
# This is the sshd server system-wide configuration file. See
# sshd_config(5) for more information.
# This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin
# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented. Uncommented options override the
# default value.
Port 22
AddressFamily inet
#ListenAddress 0.0.0.0
#ListenAddress ::
#HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_ecdsa_key
#HostKey /etc/ssh/ssh_host_ed25519_key
# Ciphers and keying
#RekeyLimit default none
# Logging
#SyslogFacility AUTH
#LogLevel INFO
# Authentication:
#LoginGraceTime 2m
PermitRootLogin no
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10
PubkeyAuthentication yes
# Expect .ssh/authorized_keys2 to be disregarded by default in future.
AuthorizedKeysFile .ssh/authorized_keys
#AuthorizedPrincipalsFile none
#AuthorizedKeysCommand none
#AuthorizedKeysCommandUser nobody
# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#HostbasedAuthentication no
# Change to yes if you don't trust ~/.ssh/known_hosts for
# HostbasedAuthentication
#IgnoreUserKnownHosts no
# Don't read the user's ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes
# To disable tunneled clear text passwords, change to no here!
PasswordAuthentication no
#PermitEmptyPasswords no
# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication yes
# Kerberos options
#KerberosAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no
# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes
#GSSAPIStrictAcceptorCheck yes
#GSSAPIKeyExchange no
# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication. Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes
# USER ADDED
#
AuthenticationMethods publickey,keyboard-interactive
#AllowAgentForwarding yes
#AllowTcpForwarding yes
#GatewayPorts no
X11Forwarding no
#X11DisplayOffset 10
#X11UseLocalhost yes
#PermitTTY yes
PrintMotd no
#PrintLastLog yes
#TCPKeepAlive yes
#UseLogin no
#UsePrivilegeSeparation sandbox
#PermitUserEnvironment no
#Compression delayed
#ClientAliveInterval 0
#ClientAliveCountMax 3
#UseDNS no
#PidFile /var/run/sshd.pid
#MaxStartups 10:30:100
#PermitTunnel no
#ChrootDirectory none
#VersionAddendum none
# no default banner path
#Banner none
# Allow client to pass locale environment variables
AcceptEnv LANG LC_*
# override default of no subsystems
Subsystem sftp /usr/lib/openssh/sftp-server
# Example of overriding settings on a per-user basis
#Match User anoncvs
# X11Forwarding no
# AllowTcpForwarding no
# PermitTTY no
# ForceCommand cvs server
$ cat /etc/pam.d/sshd
# PAM configuration for the Secure Shell service
# USER COMMENTED
#
## Standard Un*x authentication.
#@include common-auth
# Disallow non-root logins when /etc/nologin exists.
account required pam_nologin.so
# Uncomment and edit /etc/security/access.conf if you need to set complex
# access limits that are hard to express in sshd_config.
# account required pam_access.so
# Standard Un*x authorization.
@include common-account
# SELinux needs to be the first session rule. This ensures that any
# lingering context has been cleared. Without this it is possible that a
# module could execute code in the wrong domain.
session [success=ok ignore=ignore module_unknown=ignore default=bad] pam_selinux.so close
# Set the loginuid process attribute.
session required pam_loginuid.so
# Create a new session keyring.
session optional pam_keyinit.so force revoke
# Standard Un*x session setup and teardown.
@include common-session
# Print the message of the day upon successful login.
# 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
session optional pam_motd.so noupdate
# Print the status of the user's mailbox upon successful login.
session optional pam_mail.so standard noenv # [1]
# Set up user limits from /etc/security/limits.conf.
session required pam_limits.so
# Read environment variables from /etc/environment and
# /etc/security/pam_env.conf.
session required pam_env.so # [1]
# In Debian 4.0 (etch), locale-related environment variables were moved to
# /etc/default/locale, so read that as well.
session required pam_env.so user_readenv=1 envfile=/etc/default/locale
# 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
# Standard Un*x password updating.
@include common-password
# USER ADDED
#
auth [success=1 default=ignore] pam_succeed_if.so user ingroup 2faexempt
auth sufficient pam_google_authenticator.so
Respuesta1
Pensé en una manera de hacerlo funcionar. Parece extremadamente complicado, pero funciona.
No me parece seguro.
$ cat relevant section of /etc/pam.d/sshd
...
# USER COMMENTED
#
## Standard Un*x authentication.
#@include common-auth
...
# USER ADDED
#
auth [success=1 default=ignore] pam_succeed_if.so user ingroup 2faexempt
auth requisite pam_google_authenticator.so
auth required pam_permit.so