Bug#1069849: publickey auth does not work when GSSAPI is also used

Package: openssh-server
Version: 1:8.4p1-5+deb11u3
Severity: important
X-Debbugs-Cc: [email protected]

  Hi,

  In an kerberos environment, I'm gradually migrating machines from
bullseye to bookworm. Doing this, I observe a regression concerning
openssh-server.

  Openssh is configurated to allow kerberos authentification.
sshd_config has the following lines:
GSSAPIAuthentication yes
GSSAPIKeyExchange yes
GSSAPIStoreCredentialsOnRekey yes
and ssh_config has the following lines:
Host *
    GSSAPIDelegateCredentials yes
    GSSAPIKeyExchange yes
    GSSAPITrustDNS yes

  When trying to log from a kerberos account into a remote local
(non kerberos) account with a public key, it works on bulleyes machines,
but on bookworm machines, I got the following error:
$ ssh -v -l remote-local-login bookworm-machine
[...]
OpenSSH_9.2p1 Debian-2+deb12u2, OpenSSL 3.0.11 19 Sep 2023
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Reading configuration data /etc/ssh/ssh_config.d/local.conf
debug1: /etc/ssh/ssh_config.d/local.conf line 6: Applying options for *
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug1: Connecting to bookworm-machine.domain.fr [10.0.0.3] port 22.
debug1: Connection established.
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_rsa type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_rsa-cert type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_ecdsa type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_ecdsa-cert type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_ecdsa_sk type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_ecdsa_sk-cert type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_ed25519 type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_ed25519-cert type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_ed25519_sk type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_ed25519_sk-cert type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_xmss type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_xmss-cert type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_dsa type -1
debug1: identity file /home/domain.fr/kerberos-user/.ssh/id_dsa-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_9.2p1 Debian-2+deb12u2
debug1: Remote protocol version 2.0, remote software version OpenSSH_9.2p1 Debian-2+deb12u2
debug1: compat_banner: match: OpenSSH_9.2p1 Debian-2+deb12u2 pat OpenSSH* compat 0x04000000
debug1: Authenticating to bookworm-machine.domain.fr:22 as 'remote-local-login'
debug1: load_hostkeys: fopen /home/domain.fr/kerberos-user/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug1: Offering GSSAPI proposal: gss-group14-sha256-toWM5Slw5Ew8Mqkay+al2g==,gss-group16-sha512-toWM5Slw5Ew8Mqkay+al2g==,gss-nistp256-sha256-toWM5Slw5Ew8Mqkay+al2g==,gss-curve25519-sha256-toWM5Slw5Ew8Mqkay+al2g==,gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group14-sha256-eipGX3TCiQSrx573bT1o1Q==,gss-group16-sha512-eipGX3TCiQSrx573bT1o1Q==,gss-nistp256-sha256-eipGX3TCiQSrx573bT1o1Q==,gss-curve25519-sha256-eipGX3TCiQSrx573bT1o1Q==,gss-group14-sha1-eipGX3TCiQSrx573bT1o1Q==,gss-gex-sha1-eipGX3TCiQSrx573bT1o1Q==
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: gss-group14-sha256-toWM5Slw5Ew8Mqkay+al2g==
debug1: kex: host key algorithm: ssh-ed25519
debug1: kex: server->client cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: client->server cipher: [email protected] MAC: <implicit> compression: none
debug1: Calling gss_init_sec_context
debug1: Delegating credentials
debug1: Received GSSAPI_COMPLETE
debug1: Calling gss_init_sec_context
debug1: Delegating credentials
debug1: Rekey has happened - updating saved versions
debug1: ssh_packet_send2_wrapped: resetting send seqnr 3
debug1: rekey out after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: ssh_packet_read_poll2: resetting read seqnr 3
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey in after 134217728 blocks
debug1: get_agent_identities: agent returned 1 keys
debug1: Will attempt key: [email protected]@di3937su RSA SHA256:LVQ9Rw8lBcFd5DPN0NXfU8Heo2+7sBrEhzkTdNgcDVA agent
debug1: Will attempt key: /home/domain.fr/kerberos-user/.ssh/id_rsa
debug1: Will attempt key: /home/domain.fr/kerberos-user/.ssh/id_ecdsa
debug1: Will attempt key: /home/domain.fr/kerberos-user/.ssh/id_ecdsa_sk
debug1: Will attempt key: /home/domain.fr/kerberos-user/.ssh/id_ed25519
debug1: Will attempt key: /home/domain.fr/kerberos-user/.ssh/id_ed25519_sk
debug1: Will attempt key: /home/domain.fr/kerberos-user/.ssh/id_xmss
debug1: Will attempt key: /home/domain.fr/kerberos-user/.ssh/id_dsa
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,[email protected],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,[email protected],[email protected],ssh-dss,ssh-rsa,rsa-sha2-256,rsa-sha2-512>
debug1: kex_input_ext_info: [email protected]=<0>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,gssapi-with-mic,password
debug1: Next authentication method: publickey
debug1: Offering public key: [email protected]@di3937su RSA SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX agent
debug1: Server accepts key: [email protected]@di3937su RSA SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX agent
sign_and_send_pubkey: internal error: initial hostkey not recorded

  Reading https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/2028282
and https://bugzilla.mindrot.org/show_bug.cgi?id=3406
I workaround this bug by running my command prefixed by 'env KRB5CCNAME="" ssh ...'

  The bugzilla bug report suggests a fix (I did not try it).

  Regards,
    Vincent

-- System Information:
Debian Release: 11.8
  APT prefers oldstable-security
  APT policy: (990, 'oldstable-security'), (990, 'oldstable'), (500, 'stable-updates'), (500, 'stable-security'), (500, 'oldstable-updates'), (500, 'oldoldstable-updates'), (500, 'oldoldstable'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.1.0-0.deb11.13-amd64 (SMP w/1 CPU thread; PREEMPT)
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages openssh-server depends on:
ii  adduser                3.118+deb11u1
ii  debconf [debconf-2.0]  1.5.77
ii  dpkg                   1.20.13
ii  libaudit1              1:3.0-2
ii  libc6                  2.31-13+deb11u7
ii  libcom-err2            1.46.2-2
ii  libcrypt1              1:4.4.18-4
ii  libgssapi-krb5-2       1.18.3-6+deb11u4
ii  libkrb5-3              1.18.3-6+deb11u4
ii  libpam-modules         1.4.0-9+deb11u1
ii  libpam-runtime         1.4.0-9+deb11u1
ii  libpam0g               1.4.0-9+deb11u1
ii  libselinux1            3.1-3
ii  libssl1.1              1.1.1w-0+deb11u1
ii  libsystemd0            247.3-7+deb11u4
ii  libwrap0               7.6.q-31
ii  lsb-base               11.1.0
ii  openssh-client         1:8.4p1-5+deb11u3
ii  openssh-sftp-server    1:8.4p1-5+deb11u3
ii  procps                 2:3.3.17-5
ii  runit-helper           2.10.3
ii  ucf                    3.0043
ii  zlib1g                 1:1.2.11.dfsg-2+deb11u2

Versions of packages openssh-server recommends:
ii  libpam-systemd [logind]  247.3-7+deb11u4
ii  ncurses-term             6.2+20201114-2+deb11u2
ii  xauth                    1:1.1-1

Versions of packages openssh-server suggests:
pn  molly-guard   <none>
pn  monkeysphere  <none>
pn  ssh-askpass   <none>
pn  ufw           <none>

-- debconf information excluded