Bug#955725: openssh-server: working passwordless authentication with ssh-keygen key suddently fails

[Eric Valette <eric.valette@free.fr>]

Package: openssh-server
Version: 1:8.2p1-4
Severity: important

I had setup rsync backup without passord that was perfectly working. Suddently it was
stuck by asking remote passwd for each rsync command. ssh passwordless for root user
was indeed borken.

Even regenerating the key in case of lengh and algorythm change did not fix the
problem. Did something change in the config?

It started April 2.

-- System Information:
Debian Release: bullseye/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 5.4.30 (SMP w/8 CPU cores; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE
Locale: LANG=fr_FR.UTF8, LC_CTYPE=fr_FR.UTF8 (charmap=UTF-8), LANGUAGE= (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages openssh-server depends on:
ii  adduser                3.118
ii  debconf [debconf-2.0]  1.5.73
ii  dpkg                   1.20.0
ii  libaudit1              1:2.8.5-3
ii  libc6                  2.31-0experimental0
ii  libcom-err2            1.46~WIP.2019.10.03-1
ii  libcrypt1              1:4.4.15-1
ii  libgssapi-krb5-2       1.17-7
ii  libkrb5-3              1.17-7
ii  libpam-modules         1.3.1-5
ii  libpam-runtime         1.3.1-5
ii  libpam0g               1.3.1-5
ii  libselinux1            3.0-1+b2
ii  libssl1.1              1.1.1f-1
ii  libsystemd0            245.4-1
ii  libwrap0               7.6.q-30
ii  lsb-base               11.1.0
ii  openssh-client         1:8.2p1-4
ii  openssh-sftp-server    1:8.2p1-4
ii  procps                 2:3.3.16-4
ii  runit-helper           2.8.15
ii  ucf                    3.0038+nmu1
ii  zlib1g                 1:1.2.11.dfsg-2

Versions of packages openssh-server recommends:
ii  libpam-systemd [logind]  245.4-1
ii  ncurses-term             6.2-1
ii  xauth                    1:1.0.10-1

Versions of packages openssh-server suggests:
ii  ksshaskpass [ssh-askpass]  4:5.17.5-2
pn  molly-guard                <none>
pn  monkeysphere               <none>
pn  ufw                        <none>

-- debconf information:
  openssh-server/password-authentication: true
* ssh/use_old_init_script: true
* openssh-server/permit-root-login: false
  ssh/encrypted_host_key_but_no_keygen:
  ssh/vulnerable_host_keys:
  ssh/disable_cr_auth: false