Início / unix / Perguntas / 433039
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Multisync
Asked: 2018-03-24 03:21:44 +0800 CST

Login SSH sem chave e sem senha no host local não é possível, relação PAM assumida

  • 772

Gostaria de fazer login 127.0.0.1via SSH sem usar uma chave pública e senha. sshd_confige arquivos de log são fornecidos abaixo, então aqui está apenas um resumo rápido:

  • A senha das contas de usuário é excluída com passwd --delete, ou seja, o login é possível sem senha
  • PasswordAuthenticatione PermitEmptyPasswordsgeralmente é definido como no, mas é definido como yespara logins 127.0.0.0/8via Matchcondição. Os logs indicam que a Matchcondição foi analisada corretamente e foi atendida.
  • Os logs sugerem que é o PAM que está atrapalhando.

Já pesquisei bastante, mas o PAM parece ser um tema muito complexo. Ainda não entendi como o SSH e o PAM estão interconectados.

Estou executando o Linux manuel-nas 4.9.0-6-amd64 #1 SMP Debian 4.9.82-1+deb9u3 (2018-03-02) x86_64 GNU/Linux

Logs e arquivos de configuração:

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 any
#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 prohibit-password
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

#PubkeyAuthentication yes

# Expect .ssh/authorized_keys2 to be disregarded by default in future.
#AuthorizedKeysFile .ssh/authorized_keys .ssh/authorized_keys2

#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 no

# 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

#AllowAgentForwarding yes
#AllowTcpForwarding yes
#GatewayPorts no X11Forwarding yes
#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

Match Address 127.0.0.0/8
    PasswordAuthentication yes
    PermitEmptyPasswords yes

Match user diskuser
    ForceCommand internal-sftp
    ChrootDirectory /mnt/daten

Match user diskuser-privat
    ForceCommand internal-sftp
    ChrootDirectory /mnt/privat

sshdsaída de depuração:

$ /usr/sbin/sshd -p2222 -ddd
--- Beginning stripped for clarity ---
debug3: checking match for 'Address 127.0.0.0/8' user user host 127.0.0.1 addr 127.0.0.1 laddr 127.0.0.1 lport 2222
debug1: connection from 127.0.0.1 matched 'Address 127.0.0.0/8' at line 125
debug3: match found
debug3: reprocess config:126 setting PasswordAuthentication yes
debug3: reprocess config:127 setting PermitEmptyPasswords yes
debug3: checking match for 'user diskuser' user user host 127.0.0.1 addr 127.0.0.1 laddr 127.0.0.1 lport 2222
debug3: match not found
debug3: checking match for 'user diskuser-privat' user user host 127.0.0.1 addr 127.0.0.1 laddr 127.0.0.1 lport 2222
debug3: match not found
debug3: mm_answer_pwnamallow: sending MONITOR_ANS_PWNAM: 1
debug3: mm_request_send entering: type 9
debug2: monitor_read: 8 used once, disabling now
debug3: mm_getpwnamallow: waiting for MONITOR_ANS_PWNAM [preauth]
debug3: mm_request_receive_expect entering: type 9 [preauth]
debug3: mm_request_receive entering [preauth]
debug2: input_userauth_request: setting up authctxt for user [preauth]
debug3: mm_start_pam entering [preauth]
debug3: mm_request_send entering: type 100 [preauth]
debug3: mm_inform_authserv entering [preauth]
debug3: mm_request_send entering: type 4 [preauth]
debug3: mm_request_receive entering
debug3: monitor_read: checking request 100
debug1: PAM: initializing for "user"
debug1: PAM: setting PAM_RHOST to "127.0.0.1"
debug1: PAM: setting PAM_TTY to "ssh"
debug2: monitor_read: 100 used once, disabling now
debug2: input_userauth_request: try method none [preauth]
debug3: mm_auth_password entering [preauth]
debug3: mm_request_send entering: type 12 [preauth]
debug3: mm_auth_password: waiting for MONITOR_ANS_AUTHPASSWORD [preauth]
debug3: mm_request_receive_expect entering: type 13 [preauth]
debug3: mm_request_receive entering [preauth]
debug3: mm_request_receive entering
debug3: monitor_read: checking request 4
debug3: mm_answer_authserv: service=ssh-connection, style=, role=
debug2: monitor_read: 4 used once, disabling now
debug3: mm_request_receive entering
debug3: monitor_read: checking request 12
debug3: PAM: sshpam_passwd_conv called with 1 messages
debug1: PAM: password authentication failed for user: Authentication failure
debug3: mm_answer_authpassword: sending result 0
debug3: mm_request_send entering: type 13
Failed none for user from 127.0.0.1 port 36202 ssh2
debug3: mm_auth_password: user not authenticated [preauth]
debug3: userauth_finish: failure partial=0 next methods="publickey,password" [preauth]
debug3: send packet: type 51 [preauth]

/var/log/auth.logresultado:

Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: recv_rexec_state: entering fd = 5
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: ssh_msg_recv entering
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: recv_rexec_state: done
Mar 23 11:09:52 manuel-nas sshd[23081]: debug2: parse_server_config: config rexec len 563
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: rexec:56 setting PasswordAuthentication no
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: rexec:61 setting ChallengeResponseAuthentication no
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: rexec:84 setting UsePAM yes
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: rexec:89 setting X11Forwarding yes
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: rexec:93 setting PrintMotd no
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: rexec:100 setting ClientAliveInterval 0
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: rexec:101 setting ClientAliveCountMax 3
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: rexec:113 setting AcceptEnv LANG LC_*
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: rexec:116 setting Subsystem sftp\t/usr/lib/openssh/sftp-server
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: checking syntax for 'Match Address 127.0.0.0/8'
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: checking syntax for 'Match user diskuser'
Mar 23 11:09:52 manuel-nas sshd[23081]: debug3: checking syntax for 'Match user diskuser-privat'
Mar 23 11:09:52 manuel-nas sshd[23081]: debug1: sshd version OpenSSH_7.4, OpenSSL 1.0.2l  25 May 2017
Mar 23 11:09:52 manuel-nas sshd[23081]: debug1: private host key #0: ssh-rsa SHA256:< removed for confidentiality >
Mar 23 11:09:52 manuel-nas sshd[23081]: debug1: private host key #1: ecdsa-sha2-nistp256 SHA256:< removed for confidentiality >
Mar 23 11:09:52 manuel-nas sshd[23081]: debug1: private host key #2: ssh-ed25519 SHA256:< removed for confidentiality >
Mar 23 11:09:52 manuel-nas sshd[23081]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=127.0.0.1  user=user

sshsaída: Nota: Nos logs, posso ver que minha tentativa de login já foi rejeitada quando o prompt de senha aparece

$ ssh 127.0.0.1 -p2222
[email protected]'s password:
ssh openssh

1 respostas

  1. Best Answer

    Na configuração do PAM (que é específica da distribuição), certifique-se de que a linha pam_unix.so para sshd tenha o argumento nullok , por exemplo:

    auth      required  pam_unix.so try_first_pass nullok

    Caso contrário, o pam_unix impedirá isso, cf. a página de manual do pam_unix :

    A ação padrão deste módulo é não permitir o acesso do usuário a um serviço se sua senha oficial estiver em branco. O argumento nullok substitui esse padrão.

    • 2

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