Ubuntu
openssh package

ServerAlive and ClientAlive not working when using Tunnel=point-to-point

Bug #1694395 reported by Marco Basso
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
openssh (Ubuntu)
New
Undecided
Unassigned

Bug Description

The full IPv4 tunnel don't quit the ssh process when network connectivity fails, thus invalidating the potential benefit of Server/ClientAliveInterval and Server/ClientAliveCountMax.

Here are some config file snippets.

--------------------------------------------------------------------------------

# cat /etc/ssh/sshd_config |uncomment
GSSAPIAuthentication no
ChallengeResponseAuthentication yes
PermitRootLogin yes
Port 22
Protocol 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
UsePrivilegeSeparation yes
KeyRegenerationInterval 3600
ServerKeyBits 1024
SyslogFacility AUTH
LogLevel INFO
LoginGraceTime 120
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
IgnoreRhosts yes
RhostsRSAAuthentication no
HostbasedAuthentication no
PermitEmptyPasswords no
ChallengeResponseAuthentication no
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
UsePAM yes
PasswordAuthentication no
UseDNS no
PermitTunnel yes
ClientAliveInterval 20
ClientAliveCountMax 3
Match User sshtun
  ForceCommand /bin/true

# cat /etc/ssh/ssh_config |uncomment
Host *
SendEnv LANG LC_*
HashKnownHosts yes
GSSAPIAuthentication yes
GSSAPIDelegateCredentials no
ServerAliveInterval 20
ServerAliveCountMax 3

# grep sshtun /etc/passwd
sshtun:x:1000:1000:,,,:/home/sshtun:/bin/false

# grep sshtun /etc/shadow
sshtun:!:17102:0:99999:7:::

# grep -A6 tun203 /etc/network/interfaces.d/tunnels.cfg
auto tun203
iface tun203 inet manual
 pre-up /sbin/ifup venet0:0 >/dev/null 2>&1 || true
 pre-up /sbin/ip tuntap add $IFACE mode tun user sshtun
 pre-up /sbin/ip link set dev $IFACE up
 pre-up /sbin/ip address add 100.127.0.2/32 dev lo >/dev/null 2>&1 || true
 post-up /sbin/ip route add 100.127.0.3 dev $IFACE src 100.127.0.2 >/dev/null 2>&1 || true
 post-down /sbin/ip link del $IFACE

--------------------------------------------------------------------------------

The purpose of this configuration is to establish a full IPv4 tunnel between initiatorserver.example.com and w1.example.com using tun203 iface name on both side.

Down below an ssh command that don't show any "client_input_global_request: rtype <email address hidden> want_reply 1" at the end.

--------------------------------------------------------------------------------

sudo -u sshtun ssh -N -T -i /home/sshtun/.ssh/id_ed25519 -w 203:203 -o LogLevel=DEBUG3 -o ServerAliveInterval=30 -o ServerAliveCountMax=3 -o ConnectTimeout=10 -o ExitOnForwardFailure=yes -o Tunnel=point-to-point <email address hidden>
debug1: Reading configuration data /home/sshtun/.ssh/config
debug1: /home/sshtun/.ssh/config line 1: Applying options for *.example.com
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to w1.example.com [203.0.113.1] port 22.
debug2: fd 3 setting O_NONBLOCK
debug1: fd 3 clearing O_NONBLOCK
debug1: Connection established.
debug3: timeout: 10000 ms remain after connect
debug1: identity file /home/sshtun/.ssh/id_ed25519 type 4
debug1: key_load_public: No such file or directory
debug1: identity file /home/sshtun/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.7p1 Debian-5+deb8u3
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.7p1 Debian-5+deb8u3
debug1: match: OpenSSH_6.7p1 Debian-5+deb8u3 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug3: load_hostkeys: loading entries for host "w1.example.com" from file "/home/sshtun/.ssh/known_hosts"
debug3: load_hostkeys: found key type ED25519 in file /home/sshtun/.ssh/known_hosts:5
debug3: load_hostkeys: loaded 1 keys
debug3: order_hostkeyalgs: prefer hostkeyalgs: <email address hidden>,ssh-ed25519
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: <email address hidden>,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: <email address hidden>,ssh-ed25519,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,<email address hidden>,<email address hidden>,<email address hidden>,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,<email address hidden>
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,<email address hidden>,<email address hidden>,<email address hidden>,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,<email address hidden>
debug2: kex_parse_kexinit: <email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-sha2-256,hmac-sha2-512,hmac-sha1,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-md5,hmac-ripemd160,<email address hidden>,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: <email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-sha2-256,hmac-sha2-512,hmac-sha1,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-md5,hmac-ripemd160,<email address hidden>,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,<email address hidden>,zlib
debug2: kex_parse_kexinit: none,<email address hidden>,zlib
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: kex_parse_kexinit: <email address hidden>,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-ed25519
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,<email address hidden>,<email address hidden>,<email address hidden>
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,<email address hidden>,<email address hidden>,<email address hidden>
debug2: kex_parse_kexinit: <email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: kex_parse_kexinit: <email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: kex_parse_kexinit: none,<email address hidden>
debug2: kex_parse_kexinit: none,<email address hidden>
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: mac_setup: setup <email address hidden>
debug1: kex: server->client aes128-ctr <email address hidden> none
debug2: mac_setup: setup <email address hidden>
debug1: kex: client->server aes128-ctr <email address hidden> none
debug1: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ED25519 0b:09:31:ea:b1:a8:99:91:3f:d7:5a:1d:a0:71:33:40
debug3: load_hostkeys: loading entries for host "w1.example.com" from file "/home/sshtun/.ssh/known_hosts"
debug3: load_hostkeys: found key type ED25519 in file /home/sshtun/.ssh/known_hosts:5
debug3: load_hostkeys: loaded 1 keys
debug3: load_hostkeys: loading entries for host "203.0.113.1" from file "/home/sshtun/.ssh/known_hosts"
debug3: load_hostkeys: found key type ED25519 in file /home/sshtun/.ssh/known_hosts:9
debug3: load_hostkeys: loaded 1 keys
debug1: Host 'w1.example.com' is known and matches the ED25519 host key.
debug1: Found key in /home/sshtun/.ssh/known_hosts:5
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/sshtun/.ssh/id_ed25519 (0x7f54c4555e00), explicit
debug1: Authentications that can continue: publickey,keyboard-interactive
debug3: start over, passed a different list publickey,keyboard-interactive
debug3: preferred gssapi-keyex,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 ED25519 public key: /home/sshtun/.ssh/id_ed25519
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Server accepts key: pkalg ssh-ed25519 blen 51
debug2: input_userauth_pk_ok: fp 56:8e:42:a8:e0:9f:40:82:94:6f:03:18:54:25:f1:af
debug3: sign_and_send_pubkey: ED25519 56:8e:42:a8:e0:9f:40:82:94:6f:03:18:54:25:f1:af
debug1: Authentication succeeded (publickey).
Authenticated to w1.example.com ([203.0.113.1]:22).
debug1: Requesting tun unit 203 in mode 1
debug1: sys_tun_open: tun203 mode 1 fd 4
debug2: fd 4 setting O_NONBLOCK
debug3: fd 4 is O_NONBLOCK
debug1: channel 0: new [tun]
debug2: fd 3 setting TCP_NODELAY
debug3: packet_set_tos: set IP_TOS 0x10
debug1: Requesting <email address hidden>
debug1: Entering interactive session.
debug2: channel 0: open confirm rwindow 2097152 rmax 32768

--------------------------------------------------------------------------------

Please note that the tunnel works and the only thing that lacks is the non-spoofable alive messages system that will quit the process when the ssh vpn partners are unreachable.

Here below there's another ssh command, made by the same initiatorserver, that uses only TCP forwarding.
In the log below, please find the lines with "client_input_global_request: rtype <email address hidden> want_reply 1" near the end.
Those lines show that the alive messages system is working fine, and those lines are what is missing in the previous scenario.

--------------------------------------------------------------------------------

sudo -u sshtun ssh -N -T -i /home/sshtun/.ssh/id_ed25519 -L55203:127.0.0.1:55203 -R55302:127.0.0.1:55302 -o LogLevel=DEBUG3 -o ServerAliveInterval=30 -o ServerAliveCountMax=3 -o ConnectTimeout=10 -o ExitOnForwardFailure=yes -o Tunnel=no <email address hidden>
debug1: Reading configuration data /home/sshtun/.ssh/config
debug1: /home/sshtun/.ssh/config line 1: Applying options for *.example.com
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to w1.example.com [203.0.113.1] port 22.
debug2: fd 3 setting O_NONBLOCK
debug1: fd 3 clearing O_NONBLOCK
debug1: Connection established.
debug3: timeout: 10000 ms remain after connect
debug1: identity file /home/sshtun/.ssh/id_ed25519 type 4
debug1: key_load_public: No such file or directory
debug1: identity file /home/sshtun/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.7p1 Debian-5+deb8u3
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.7p1 Debian-5+deb8u3
debug1: match: OpenSSH_6.7p1 Debian-5+deb8u3 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug3: load_hostkeys: loading entries for host "w1.example.com" from file "/home/sshtun/.ssh/known_hosts"
debug3: load_hostkeys: found key type ED25519 in file /home/sshtun/.ssh/known_hosts:5
debug3: load_hostkeys: loaded 1 keys
debug3: order_hostkeyalgs: prefer hostkeyalgs: <email address hidden>,ssh-ed25519
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: <email address hidden>,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: <email address hidden>,ssh-ed25519,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,<email address hidden>,<email address hidden>,<email address hidden>,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,<email address hidden>
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,<email address hidden>,<email address hidden>,<email address hidden>,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,<email address hidden>
debug2: kex_parse_kexinit: <email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-sha2-256,hmac-sha2-512,hmac-sha1,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-md5,hmac-ripemd160,<email address hidden>,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: <email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-sha2-256,hmac-sha2-512,hmac-sha1,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-md5,hmac-ripemd160,<email address hidden>,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,<email address hidden>,zlib
debug2: kex_parse_kexinit: none,<email address hidden>,zlib
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: kex_parse_kexinit: <email address hidden>,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-ed25519
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,<email address hidden>,<email address hidden>,<email address hidden>
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,<email address hidden>,<email address hidden>,<email address hidden>
debug2: kex_parse_kexinit: <email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: kex_parse_kexinit: <email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,<email address hidden>,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: kex_parse_kexinit: none,<email address hidden>
debug2: kex_parse_kexinit: none,<email address hidden>
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: mac_setup: setup <email address hidden>
debug1: kex: server->client aes128-ctr <email address hidden> none
debug2: mac_setup: setup <email address hidden>
debug1: kex: client->server aes128-ctr <email address hidden> none
debug1: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ED25519 0b:09:31:ea:b1:a8:99:91:3f:d7:5a:1d:a0:71:33:40
debug3: load_hostkeys: loading entries for host "w1.example.com" from file "/home/sshtun/.ssh/known_hosts"
debug3: load_hostkeys: found key type ED25519 in file /home/sshtun/.ssh/known_hosts:5
debug3: load_hostkeys: loaded 1 keys
debug3: load_hostkeys: loading entries for host "203.0.113.1" from file "/home/sshtun/.ssh/known_hosts"
debug3: load_hostkeys: found key type ED25519 in file /home/sshtun/.ssh/known_hosts:9
debug3: load_hostkeys: loaded 1 keys
debug1: Host 'w1.example.com' is known and matches the ED25519 host key.
debug1: Found key in /home/sshtun/.ssh/known_hosts:5
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/sshtun/.ssh/id_ed25519 (0x7ff7157c1ed0), explicit
debug1: Authentications that can continue: publickey,keyboard-interactive
debug3: start over, passed a different list publickey,keyboard-interactive
debug3: preferred gssapi-keyex,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 ED25519 public key: /home/sshtun/.ssh/id_ed25519
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Server accepts key: pkalg ssh-ed25519 blen 51
debug2: input_userauth_pk_ok: fp 56:8e:42:a8:e0:9f:40:82:94:6f:03:18:54:25:f1:af
debug3: sign_and_send_pubkey: ED25519 56:8e:42:a8:e0:9f:40:82:94:6f:03:18:54:25:f1:af
debug1: Authentication succeeded (publickey).
Authenticated to w1.example.com ([203.0.113.1]:22).
debug1: Local connections to LOCALHOST:55203 forwarded to remote address 127.0.0.1:55203
debug3: channel_setup_fwd_listener_tcpip: type 2 wildcard 0 addr NULL
debug3: sock_set_v6only: set socket 4 IPV6_V6ONLY
debug1: Local forwarding listening on ::1 port 55203.
debug2: fd 4 setting O_NONBLOCK
debug3: fd 4 is O_NONBLOCK
debug1: channel 0: new [port listener]
debug1: Local forwarding listening on 127.0.0.1 port 55203.
debug2: fd 5 setting O_NONBLOCK
debug3: fd 5 is O_NONBLOCK
debug1: channel 1: new [port listener]
debug1: Remote connections from LOCALHOST:55302 forwarded to local address 127.0.0.1:55302
debug2: fd 3 setting TCP_NODELAY
debug3: packet_set_tos: set IP_TOS 0x10
debug1: Requesting <email address hidden>
debug1: Entering interactive session.
debug1: remote forward success for: listen 55302, connect 127.0.0.1:55302
debug1: All remote forwarding requests processed
debug1: client_input_global_request: rtype <email address hidden> want_reply 1
debug1: client_input_global_request: rtype <email address hidden> want_reply 1
debug1: client_input_global_request: rtype <email address hidden> want_reply 1
debug1: client_input_global_request: rtype <email address hidden> want_reply 1
Timeout, server w1.example.com not responding.

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