openssh: allow configuration of hostkey type

Allow selection of host key types used by openssh via PACKAGECONFIG.
Any combination of hostkey-rsa, hostkey-ecdsa and hostkey-ed25519 can be
specified. Default to just generating ecdsa keys.

The current default generates all three keys. This can take a
significant amount of time on first boot. Having all three keys does not
significantly increase compatability. Also RSA keys are being deprecated
as they are no longer considered secure. Using just an ecdsa key reduces
key generation time by roughly 75%.

Signed-off-by: Matthew Bullock <mbullock@thegoodpenguin.co.uk>
---
 .../openssh/openssh_9.7p1.bb                  | 29 ++++++++++++++++---
 1 file changed, 25 insertions(+), 4 deletions(-)

On Thu, 27 Jun 2024 at 14:19, Matthew Bullock via
lists.openembedded.org
<mbullock=thegoodpenguin.co.uk@lists.openembedded.org> wrote:
>
> Allow selection of host key types used by openssh via PACKAGECONFIG.
> Any combination of hostkey-rsa, hostkey-ecdsa and hostkey-ed25519 can be
> specified. Default to just generating ecdsa keys.
>
> The current default generates all three keys. This can take a
> significant amount of time on first boot. Having all three keys does not
> significantly increase compatability. Also RSA keys are being deprecated
> as they are no longer considered secure. Using just an ecdsa key reduces
> key generation time by roughly 75%.
>
> Signed-off-by: Matthew Bullock <mbullock@thegoodpenguin.co.uk>
> ---
>  .../openssh/openssh_9.7p1.bb                  | 29 ++++++++++++++++---
>  1 file changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/meta/recipes-connectivity/openssh/openssh_9.7p1.bb b/meta/recipes-connectivity/openssh/openssh_9.7p1.bb
> index ab453f7bbe..0bc14c5553 100644
> --- a/meta/recipes-connectivity/openssh/openssh_9.7p1.bb
> +++ b/meta/recipes-connectivity/openssh/openssh_9.7p1.bb
> @@ -56,7 +56,7 @@ DEPENDS += "${@bb.utils.contains('DISTRO_FEATURES', 'systemd', 'systemd', '', d)
>
>  # systemd-sshd-socket-mode means installing sshd.socket
>  # and systemd-sshd-service-mode corresponding to sshd.service
> -PACKAGECONFIG ??= "systemd-sshd-socket-mode"
> +PACKAGECONFIG ??= "systemd-sshd-socket-mode hostkey-ecdsa"
>  PACKAGECONFIG[fido2] = "--with-security-key-builtin,--disable-security-key,libfido2"
>  PACKAGECONFIG[kerberos] = "--with-kerberos5,--without-kerberos5,krb5"
>  PACKAGECONFIG[ldns] = "--with-ldns,--without-ldns,ldns"
> @@ -64,6 +64,9 @@ PACKAGECONFIG[libedit] = "--with-libedit,--without-libedit,libedit"
>  PACKAGECONFIG[manpages] = "--with-mantype=man,--with-mantype=cat"
>  PACKAGECONFIG[systemd-sshd-socket-mode] = ""
>  PACKAGECONFIG[systemd-sshd-service-mode] = ""
> +PACKAGECONFIG[hostkey-rsa] = ""
> +PACKAGECONFIG[hostkey-ecdsa] = ""
> +PACKAGECONFIG[hostkey-ed25519] = ""
>
>  EXTRA_AUTORECONF += "--exclude=aclocal"
>
> @@ -127,13 +130,31 @@ do_install:append () {
>         install -m 644 ${UNPACKDIR}/volatiles.99_sshd ${D}/${sysconfdir}/default/volatiles/99_sshd
>         install -m 0755 ${S}/contrib/ssh-copy-id ${D}${bindir}
>
> +        # Enable specific ssh host keys
> +       sed -i '/HostKey/d' ${D}${sysconfdir}/ssh/sshd_config
> +       if ${@bb.utils.contains('PACKAGECONFIG','hostkey-rsa','true','false',d)}; then
> +           echo "HostKey /etc/ssh/ssh_host_rsa_key" >> ${D}${sysconfdir}/ssh/sshd_config
> +        fi
> +       if ${@bb.utils.contains('PACKAGECONFIG','hostkey-ecdsa','true','false',d)}; then
> +           echo "HostKey /etc/ssh/ssh_host_ecdsa_key" >> ${D}${sysconfdir}/ssh/sshd_config
> +        fi
> +       if ${@bb.utils.contains('PACKAGECONFIG','hostkey-ed25519','true','false',d)}; then
> +           echo "HostKey /etc/ssh/ssh_host_ed25519_key" >> ${D}${sysconfdir}/ssh/sshd_config
> +        fi
> +
>         # Create config files for read-only rootfs
>         install -d ${D}${sysconfdir}/ssh
>         install -m 644 ${D}${sysconfdir}/ssh/sshd_config ${D}${sysconfdir}/ssh/sshd_config_readonly
>         sed -i '/HostKey/d' ${D}${sysconfdir}/ssh/sshd_config_readonly
> -       echo "HostKey /var/run/ssh/ssh_host_rsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
> -       echo "HostKey /var/run/ssh/ssh_host_ecdsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
> -       echo "HostKey /var/run/ssh/ssh_host_ed25519_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
> +       if ${@bb.utils.contains('PACKAGECONFIG','hostkey-rsa','true','false',d)}; then
> +           echo "HostKey /var/run/ssh/ssh_host_rsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
> +        fi
> +       if ${@bb.utils.contains('PACKAGECONFIG','hostkey-ecdsa','true','false',d)}; then
> +           echo "HostKey /var/run/ssh/ssh_host_ecdsa_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
> +        fi
> +       if ${@bb.utils.contains('PACKAGECONFIG','hostkey-ed25519','true','false',d)}; then
> +           echo "HostKey /var/run/ssh/ssh_host_ed25519_key" >> ${D}${sysconfdir}/ssh/sshd_config_readonly
> +        fi
>
>         install -d ${D}${systemd_system_unitdir}
>         if ${@bb.utils.contains('PACKAGECONFIG','systemd-sshd-socket-mode','true','false',d)}; then
> --
> 2.43.0
>

Reviewed-by: Andrew Murray <amurray@thegoodpenguin.co.uk>

Thanks,

Andrew Murray