[PATCH] openssh: allow configuration of hostkey type

[PATCH] openssh: allow configuration of hostkey type

[Matthew Bullock]

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

Re: [OE-core] [PATCH] openssh: allow configuration of hostkey type

[Andrew Murray]

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

Re: [OE-core] [PATCH] openssh: allow configuration of hostkey type

[Rasmus Villemoes]

"Matthew Bullock via lists.openembedded.org"
<mbullock=thegoodpenguin.co.uk@lists.openembedded.org> writes:

> 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

This will break our setup. We rely on the sshd_config including the

Include /etc/ssh/sshd_config.d/*.conf

directive and put a hostkeys.conf file in there, specifying the host
key(s) types and paths we need (we have a readonly rootfs, but do have a
place for persistent and per-machine stuff like this, so we use neither
of the /etc or /var/run paths).

I suppose we can remove hostkey-ecdsa and any other hostkey-* that may
appear in PACKAGECONFIG in the future. But I think others may, for
example, have a .bbappend where they supply a whole alternative
sshd_config with similar explicit HostKey settings, and this would also
break for them.

So perhaps this could/should be guarded by 'grep -i ^hostkey' not
finding anything in sshd_config or sshd_config.d/*.conf ?

Rasmus