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

[Henning Schild <henning.schild@siemens.com>]

Am Thu, 13 Dec 2018 09:56:58 +0100
schrieb Harald Seiler <hws@denx.de>:

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

Do we need the start? Is that not in fact taking us into the same
issue? ... i guess that is the "--no-block".

Henning

> +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" }