使用 ssh agent forward 和 libpam-ssh 无需密码即可连接到服务器上的特定用户

Question

我正在尝试实现设置。

• 我可以使用 ssh 的 RSA 密钥将用户 A 连接到我的服务器。
• 但我不知道如何转发代理以与 libpam-ssh 一起使用。

目标是制作无密码的 sudo 命令。

顺便说一下，我使用 Debian (Buster)。

ssh       su
A ------> B:user X ------> B:userY
    ^                ^
using A's        using A's
 ssh key           ssh key

这可能吗？

Feb 22 11:00:11 jeremydev sshd[4050]: Accepted publickey for juniko from 127.0.0.1 port 55484 ssh2: RSA SHA256:N1N2OMouB8WTpQtYEAt69Iar79D3vOdhIHo96kgbDbU
Feb 22 11:00:11 jeremydev sshd[4050]: pam_unix(sshd:session): session opened for user juniko by (uid=0)
Feb 22 11:00:11 jeremydev systemd-logind[513]: New session 100 of user juniko.
Feb 22 11:00:14 jeremydev sudo[4169]: pam_ssh_agent_auth: Beginning pam_ssh_agent_auth for user juniko
Feb 22 11:00:14 jeremydev sudo[4169]: pam_ssh_agent_auth: Attempting authentication: `juniko' as `juniko' using /etc/ssh/sudo_authorized_keys
Feb 22 11:00:14 jeremydev sudo[4169]: pam_ssh_agent_auth: Contacted ssh-agent of user juniko (1000)
Feb 22 11:00:14 jeremydev sudo[4169]: pam_ssh_agent_auth: Failed Authentication: `juniko' as `juniko' using /etc/ssh/sudo_authorized_keys

以下是连接日志示例：

OpenSSH_8.1p1 Ubuntu-5, OpenSSL 1.1.1d  10 Sep 2019
debug1: Reading configuration data /home/kwaadpepper/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: resolving "example.ovh" port 443
debug2: ssh_connect_direct
debug1: Connecting to example.ovh [XXX.XXX.XXX.XXX] port 443.
debug1: Connection established.
debug1: identity file .ssh/id_rsa type 0
debug1: identity file .ssh/id_rsa-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.1p1 Ubuntu-5
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.9p1
debug1: match: OpenSSH_7.9p1 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to example.ovh:443 as 'juniko'
debug3: put_host_port: [example.ovh]:443
debug3: hostkeys_foreach: reading file "/home/kwaadpepper/.ssh/known_hosts"
debug3: record_hostkey: found key type ECDSA in file /home/kwaadpepper/.ssh/known_hosts:1
debug3: load_hostkeys: loaded 1 keys from [example.ovh]:443
debug3: order_hostkeyalgs: prefer hostkeyalgs: [email protected],[email protected],[email protected],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521
debug3: send packet: type 20
debug1: SSH2_MSG_KEXINIT sent
debug3: receive packet: type 20
debug1: SSH2_MSG_KEXINIT received
debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,[email protected],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,ext-info-c
debug2: host key algorithms: [email protected],[email protected],[email protected],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,[email protected],[email protected],[email protected],[email protected],ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
debug2: ciphers ctos: [email protected],aes128-ctr,aes192-ctr,aes256-ctr,[email protected],[email protected]
debug2: ciphers stoc: [email protected],aes128-ctr,aes192-ctr,aes256-ctr,[email protected],[email protected]
debug2: MACs ctos: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,[email protected],zlib
debug2: compression stoc: none,[email protected],zlib
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,[email protected],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1
debug2: host key algorithms: rsa-sha2-512,rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256,ssh-ed25519
debug2: ciphers ctos: [email protected],aes128-ctr,aes192-ctr,aes256-ctr,[email protected],[email protected]
debug2: ciphers stoc: [email protected],aes128-ctr,aes192-ctr,aes256-ctr,[email protected],[email protected]
debug2: MACs ctos: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,[email protected]
debug2: compression stoc: none,[email protected]
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: client->server cipher: [email protected] MAC: <implicit> compression: none
debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:qWW1mY2LmZVvhYmdR4Z0z6DBLZiS2JdmmxfYu4vUR/A
debug3: put_host_port: [XXX.XXX.XXX.XXX]:443
debug3: put_host_port: [example.ovh]:443
debug3: hostkeys_foreach: reading file "/home/kwaadpepper/.ssh/known_hosts"
debug3: record_hostkey: found key type ECDSA in file /home/kwaadpepper/.ssh/known_hosts:1
debug3: load_hostkeys: loaded 1 keys from [example.ovh]:443
debug3: hostkeys_foreach: reading file "/home/kwaadpepper/.ssh/known_hosts"
debug3: record_hostkey: found key type ECDSA in file /home/kwaadpepper/.ssh/known_hosts:2
debug3: load_hostkeys: loaded 1 keys from [XXX.XXX.XXX.XXX]:443
debug1: Host '[example.ovh]:443' is known and matches the ECDSA host key.
debug1: Found key in /home/kwaadpepper/.ssh/known_hosts:1
debug3: send packet: type 21
debug2: set_newkeys: mode 1
debug1: rekey out after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug1: SSH2_MSG_NEWKEYS received
debug2: set_newkeys: mode 0
debug1: rekey in after 134217728 blocks
debug1: Will attempt key: .ssh/id_rsa RSA SHA256:N1N2OMouB8WTpQtYEAt69Iar79D3vOdhIHo96kgbDbU explicit agent
debug2: pubkey_prepare: done
debug3: send packet: type 5
debug3: receive packet: type 7
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521>
debug3: receive packet: type 6
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug3: send packet: type 50
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey
debug3: start over, passed a different list publickey
debug3: preferred gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering public key: .ssh/id_rsa RSA SHA256:N1N2OMouB8WTpQtYEAt69Iar79D3vOdhIHo96kgbDbU explicit agent
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 60
debug1: Server accepts key: .ssh/id_rsa RSA SHA256:N1N2OMouB8WTpQtYEAt69Iar79D3vOdhIHo96kgbDbU explicit agent
debug3: sign_and_send_pubkey: RSA SHA256:N1N2OMouB8WTpQtYEAt69Iar79D3vOdhIHo96kgbDbU
debug3: sign_and_send_pubkey: signing using rsa-sha2-512
debug3: send packet: type 50
debug3: receive packet: type 52
debug1: Authentication succeeded (publickey).
Authenticated to example.ovh ([XXX.XXX.XXX.XXX]:443).
debug1: channel 0: new [client-session]
debug3: ssh_session2_open: channel_new: 0
debug2: channel 0: send open
debug3: send packet: type 90
debug1: Requesting [email protected]
debug3: send packet: type 80
debug1: Entering interactive session.
debug1: pledge: network
debug3: receive packet: type 80
debug1: client_input_global_request: rtype [email protected] want_reply 0
debug3: receive packet: type 4
debug1: Remote: /home/debian/.ssh/authorized_keys:1: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
debug3: receive packet: type 4
debug1: Remote: /home/debian/.ssh/authorized_keys:1: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
debug3: receive packet: type 91
debug2: channel_input_open_confirmation: channel 0: callback start
debug1: Requesting authentication agent forwarding.
debug2: channel 0: request [email protected] confirm 0
debug3: send packet: type 98
debug2: fd 3 setting TCP_NODELAY
debug3: ssh_packet_set_tos: set IP_TOS 0x10
debug2: client_session2_setup: id 0
debug2: channel 0: request pty-req confirm 1
debug3: send packet: type 98
debug1: Sending environment.
debug3: Ignored env GJS_DEBUG_TOPICS
debug3: Ignored env SSH_AUTH_SOCK
debug3: Ignored env SESSION_MANAGER
debug3: Ignored env GNOME_TERMINAL_SCREEN
debug3: Ignored env SSH_AGENT_PID
debug3: Ignored env XDG_CURRENT_DESKTOP
debug1: Sending env LANG = fr_FR.UTF-8
debug2: channel 0: request env confirm 0
debug3: send packet: type 98
debug3: Ignored env XDG_SESSION_CLASS
debug3: Ignored env COLORTERM
debug3: Ignored env QT_IM_MODULE
debug3: Ignored env GPG_AGENT_INFO
debug3: Ignored env DESKTOP_SESSION
debug3: Ignored env USER
debug3: Ignored env XDG_MENU_PREFIX
debug3: Ignored env HOME
debug3: Ignored env GJS_DEBUG_OUTPUT
debug3: Ignored env QT4_IM_MODULE
debug3: Ignored env DBUS_SESSION_BUS_ADDRESS
debug3: Ignored env PWD
debug3: Ignored env GTK_MODULES
debug3: Ignored env XDG_CONFIG_DIRS
debug3: Ignored env WINDOWPATH
debug3: Ignored env _
debug3: Ignored env JOURNAL_STREAM
debug3: Ignored env GTK_IM_MODULE
debug3: Ignored env GNOME_DESKTOP_SESSION_ID
debug3: Ignored env MANAGERPID
debug3: Ignored env CLUTTER_IM_MODULE
debug3: Ignored env XDG_SESSION_DESKTOP
debug3: Ignored env LOGNAME
debug3: Ignored env GNOME_TERMINAL_SERVICE
debug3: Ignored env VTE_VERSION
debug3: Ignored env GNOME_SHELL_SESSION_MODE
debug3: Ignored env PATH
debug3: Ignored env XMODIFIERS
debug3: Ignored env SHELL
debug3: Ignored env XDG_RUNTIME_DIR
debug3: Ignored env XDG_SESSION_TYPE
debug3: Ignored env QT_ACCESSIBILITY
debug3: Ignored env XDG_DATA_DIRS
debug3: Ignored env USERNAME
debug3: Ignored env INVOCATION_ID
debug3: Ignored env SHLVL
debug3: Ignored env XAUTHORITY
debug3: Ignored env IM_CONFIG_CHECK_ENV
debug3: Ignored env DISPLAY
debug3: Ignored env TERM
debug3: Ignored env GDMSESSION
debug3: Ignored env IM_CONFIG_PHASE
debug3: Ignored env OLDPWD
debug3: Ignored env ZSH
debug3: Ignored env PAGER
debug3: Ignored env LESS
debug3: Ignored env LSCOLORS
debug3: Ignored env LS_COLORS
debug2: channel 0: request shell confirm 1
debug3: send packet: type 98
debug2: channel_input_open_confirmation: channel 0: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug3: receive packet: type 99
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 2097152
debug3: receive packet: type 99
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0

Answer 1

您正在寻找或ForwardAgent中的指令：/etc/ssh/ssh_config~/.ssh/config

转运代理

指定是否将与身份验证代理的连接（如果有）转发到远程计算机。该参数必须是 yes 或 no（默认值）。

应谨慎启用代理转发。能够绕过远程主机上的文件权限（对于代理的 Unix 域套接字）的用户可以通过转发的连接访问本地代理。攻击者无法从代理获取密钥材料，但他们可以对密钥执行操作，使他们能够使用加载到代理中的身份进行身份验证。

一旦您在客户端上启用它，您可以通过以下方式检查转发是否正确运行：

ssh-add -L

并验证它是否包含所需的密钥pam_ssh_agent_auth。

编辑：虽然上述配置选项（或-A您在评论中提到的命令行选项）几乎肯定会在服务器上打开一个 Unix 套接字，该套接字会转发本地 ssh 代理（以确保运行远程控制使用-v选项并检查周围的行debug1: Requesting authentication agent forwarding.是否有错误）你的 shell 初始化脚本或其他系统组件可能会用它自己的（空）代理替换转发的代理。

为了进一步调试问题，请SSH_AUTH_SOCK在登录服务器后检查变量：

printenv SSH_AUTH_SOCK

转发的代理套接字具有以下形式的路径/tmp/ssh-XXXXXXXX/agent.<pid>，其中XXXXXXXX是一些随机符号，<pid>是 shell 父进程的进程 ID（$PPIDbash 中的 的值）。即使某些东西覆盖了这个变量，您仍然可以使用以下命令找到该路径：

ls /tmp/ssh-*/agent.$PPID

并恢复它：

export SSH_AUTH_SOCK=/tmp/ssh-*/agent.$PPID

那就剩下一个问题了，谁在覆盖你的SSH_AUTH_SOCK变量。如果我不得不猜测的话，我会在狂欢init 文件（在Debian 10 /etc/profile、、、、、和上）或/etc/profile.d/*.sh~/.bash_profile~/.bash_login~/.profile/etc/bash.bashrc~/.bashrcsystemd-logind开始ssh-agent.service：

systemctl --user status ssh-agent.service