Re: [PATCH] sshd-regen-keys: Fix sshd deadlock on boot

[Claudius Heine <claudius.heine.ext@siemens.com>]

Hi Harald,

On 13/12/2018 09.56, Harald Seiler wrote:
> Currently, when sshd-regen-keys runs dpkg-reconfigure, this
> will lead to a call to `systemctl restart ssh`.  This call blocks
> forever because of course the sshd-regen-keys unit, which is a
> dependency of sshd, hasn't finished at this point and can't do so
> because it is waiting as well.
> 
> To circumvent this deadlock, this commit changes sshd-regen-keys'
> behavior so sshd is first disabled and only reenabled after the
> job is done.
> 
> Signed-off-by: Harald Seiler <hws@denx.de>
> ---
>   .../sshd-regen-keys/files/sshd-regen-keys.service     |  2 +-
>   .../sshd-regen-keys/files/sshd-regen-keys.sh          | 19 +++++++++++++++++++
>   .../sshd-regen-keys/sshd-regen-keys_0.1.bb            |  7 +++++--
>   3 files changed, 25 insertions(+), 3 deletions(-)
>   create mode 100644 meta/recipes-support/sshd-regen-keys/files/sshd-regen-keys.sh
> 
> diff --git a/meta/recipes-support/sshd-regen-keys/files/sshd-regen-keys.service b/meta/recipes-support/sshd-regen-keys/files/sshd-regen-keys.service
> index 3b8231f..a05e1a9 100644
> --- a/meta/recipes-support/sshd-regen-keys/files/sshd-regen-keys.service
> +++ b/meta/recipes-support/sshd-regen-keys/files/sshd-regen-keys.service
> @@ -10,7 +10,7 @@ ConditionPathIsReadWrite=/etc
>   Type=oneshot
>   RemainAfterExit=yes
>   Environment=DEBIAN_FRONTEND=noninteractive
> -ExecStart=/bin/sh -c "rm -v /etc/ssh/ssh_host_*_key*; dpkg-reconfigure openssh-server"
> +ExecStart=/usr/sbin/sshd-regen-keys.sh
>   ExecStartPost=-/bin/systemctl disable sshd-regen-keys.service
>   StandardOutput=syslog
>   StandardError=syslog
> diff --git a/meta/recipes-support/sshd-regen-keys/files/sshd-regen-keys.sh b/meta/recipes-support/sshd-regen-keys/files/sshd-regen-keys.sh
> new file mode 100644
> index 0000000..294e8fa
> --- /dev/null
> +++ b/meta/recipes-support/sshd-regen-keys/files/sshd-regen-keys.sh
> @@ -0,0 +1,19 @@
> +#!/usr/bin/env sh
> +
> +echo -n "SSH server is "
> +if systemctl is-enabled ssh; then
> +    SSHD_ENABLED="true"
> +    systemctl disable --no-reload ssh
> +fi
> +
> +echo "Removing keys ..."
> +rm -v /etc/ssh/ssh_host_*_key*
> +
> +echo "Regenerating keys ..."
> +dpkg-reconfigure openssh-server

Since this is part of 'meta', does it make sense to make the package 
name+service file name configurable from the bitbake configuration or is 
that too much trouble.

> +
> +if test -n $SSHD_ENABLED; then
> +    echo "Reenabling ssh server ..."
> +    systemctl enable --no-reload ssh
> +    systemctl start --no-block ssh

Should the service be stopped before? Or in other words: Does it make 
sense to differentiate between sshd enabled and started in this script?

So apart from those minor nitpicks/questions, LGTM.

Kind regards,
Claudius

> +fi
> diff --git a/meta/recipes-support/sshd-regen-keys/sshd-regen-keys_0.1.bb b/meta/recipes-support/sshd-regen-keys/sshd-regen-keys_0.1.bb
> index 02e9e25..6f12414 100644
> --- a/meta/recipes-support/sshd-regen-keys/sshd-regen-keys_0.1.bb
> +++ b/meta/recipes-support/sshd-regen-keys/sshd-regen-keys_0.1.bb
> @@ -6,9 +6,12 @@ MAINTAINER = "isar-users <isar-users@googlegroups.com>"
>   DEBIAN_DEPENDS = "openssh-server, systemd"
>   
>   SRC_URI = "file://postinst \
> -           file://sshd-regen-keys.service"
> +           file://sshd-regen-keys.service \
> +           file://sshd-regen-keys.sh"
>   
> +do_install[cleandirs] = "${D}/lib/systemd/system \
> +                         ${D}/usr/sbin"
>   do_install() {
> -    install -v -d -m 755 "${D}/lib/systemd/system"
>       install -v -m 644 "${WORKDIR}/sshd-regen-keys.service" "${D}/lib/systemd/system/sshd-regen-keys.service"
> +    install -v -m 755 "${WORKDIR}/sshd-regen-keys.sh" "${D}/usr/sbin/sshd-regen-keys.sh"
>   }
> 

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