[OE-core] [PATCH v7] openssh: Atomically generate host keys

Wed Jun 7 03:30:50 UTC 2017

On Wed, May 31, 2017 at 10:05 PM, Joshua Watt <jpewhacker at gmail.com> wrote:
> Generating the host keys atomically prevents power interruptions during
> the first boot from leaving the key files incomplete, which often
> prevents users from being able to ssh into the device.
>
> Signed-off-by: Joshua Watt <JPEWhacker at gmail.com>
> ---
>  meta/recipes-connectivity/openssh/openssh/init     | 22 ++++----------
>  .../openssh/openssh/sshd-check-key                 | 35 ++++++++++++++++++++++
>  .../openssh/openssh/sshdgenkeys.service            | 25 ++++++++--------
>  meta/recipes-connectivity/openssh/openssh_7.5p1.bb |  8 +++++
>  4 files changed, 61 insertions(+), 29 deletions(-)
>  create mode 100644 meta/recipes-connectivity/openssh/openssh/sshd-check-key
>
> diff --git a/meta/recipes-connectivity/openssh/openssh/init b/meta/recipes-connectivity/openssh/openssh/init
> index 1f63725..e02c479 100644
> --- a/meta/recipes-connectivity/openssh/openssh/init
> +++ b/meta/recipes-connectivity/openssh/openssh/init
> @@ -45,23 +45,11 @@ check_config() {
>  }
>
>  check_keys() {
> -       # create keys if necessary
> -       if [ ! -f $HOST_KEY_RSA ]; then
> -               echo "  generating ssh RSA key..."
> -               ssh-keygen -q -f $HOST_KEY_RSA -N '' -t rsa
> -       fi
> -       if [ ! -f $HOST_KEY_ECDSA ]; then
> -               echo "  generating ssh ECDSA key..."
> -               ssh-keygen -q -f $HOST_KEY_ECDSA -N '' -t ecdsa
> -       fi
> -       if [ ! -f $HOST_KEY_DSA ]; then
> -               echo "  generating ssh DSA key..."
> -               ssh-keygen -q -f $HOST_KEY_DSA -N '' -t dsa
> -       fi
> -       if [ ! -f $HOST_KEY_ED25519 ]; then
> -               echo "  generating ssh ED25519 key..."
> -               ssh-keygen -q -f $HOST_KEY_ED25519 -N '' -t ed25519
> -       fi
> +    @LIBEXECDIR@/sshd-check-key $HOST_KEY_RSA rsa
> +    @LIBEXECDIR@/sshd-check-key $HOST_KEY_ECDSA ecdsa
> +    @LIBEXECDIR@/sshd-check-key $HOST_KEY_DSA dsa
> +    @LIBEXECDIR@/sshd-check-key $HOST_KEY_ED25519 ed25519
> +    @BASE_BINDIR@/sync
>  }
>
>  export PATH="${PATH:+$PATH:}/usr/sbin:/sbin"
> diff --git a/meta/recipes-connectivity/openssh/openssh/sshd-check-key b/meta/recipes-connectivity/openssh/openssh/sshd-check-key
> new file mode 100644
> index 0000000..3afdb8b
> --- /dev/null
> +++ b/meta/recipes-connectivity/openssh/openssh/sshd-check-key
> @@ -0,0 +1,35 @@
> +#! /bin/sh
> +NAME="$1"
> +TYPE="$2"
> +
> +if [ -z "$NAME" ] || [ -z "$TYPE" ]; then
> +    echo "Usage: $0 NAME TYPE"
> +    exit 1
> +fi
> +
> +
> +if [ ! -f "$NAME" ]; then
> +    DIR="$(dirname "$NAME")"
> +
> +    echo "  generating ssh $TYPE key..."
> +    ssh-keygen -q -f "${NAME}.tmp" -N '' -t $TYPE
> +
> +    # Move (Atomically rename) files
> +    mv -f "${NAME}.tmp.pub" "${NAME}.pub"
> +
> +    # This sync does double duty: Ensuring that the data in the temporary
> +    # private key file is on disk before the rename, and ensuring that the
> +    # public key rename is completed before the private key rename, since we
> +    # switch on the existence of the private key to trigger key generation.
> +    # This does mean it is possible for the public key to exist, but be garbage
> +    # but this is OK because in that case the private key won't exist and the
> +    # keys will be regenerated.
> +    #
> +    # In the event that sync understands arguments that limit what it tries to
> +    # fsync(), we provided them. If it does not, it will simply call sync()
> +    # which is just as well
> +    sync "${NAME}.pub" "$DIR" "${NAME}.tmp"
> +
> +    mv "${NAME}.tmp" "$NAME"
> +fi
> +
> diff --git a/meta/recipes-connectivity/openssh/openssh/sshdgenkeys.service b/meta/recipes-connectivity/openssh/openssh/sshdgenkeys.service
> index 148e6ad..23fd351 100644
> --- a/meta/recipes-connectivity/openssh/openssh/sshdgenkeys.service
> +++ b/meta/recipes-connectivity/openssh/openssh/sshdgenkeys.service
> @@ -1,22 +1,23 @@
>  [Unit]
>  Description=OpenSSH Key Generation
>  RequiresMountsFor=/var /run
> -ConditionPathExists=!/var/run/ssh/ssh_host_rsa_key
> -ConditionPathExists=!/var/run/ssh/ssh_host_dsa_key
> -ConditionPathExists=!/var/run/ssh/ssh_host_ecdsa_key
> -ConditionPathExists=!/var/run/ssh/ssh_host_ed25519_key
> -ConditionPathExists=!/etc/ssh/ssh_host_rsa_key
> -ConditionPathExists=!/etc/ssh/ssh_host_dsa_key
> -ConditionPathExists=!/etc/ssh/ssh_host_ecdsa_key
> -ConditionPathExists=!/etc/ssh/ssh_host_ed25519_key
> +ConditionPathExists=|!/var/run/ssh/ssh_host_rsa_key
> +ConditionPathExists=|!/var/run/ssh/ssh_host_dsa_key
> +ConditionPathExists=|!/var/run/ssh/ssh_host_ecdsa_key
> +ConditionPathExists=|!/var/run/ssh/ssh_host_ed25519_key
> +ConditionPathExists=|!/etc/ssh/ssh_host_rsa_key
> +ConditionPathExists=|!/etc/ssh/ssh_host_dsa_key
> +ConditionPathExists=|!/etc/ssh/ssh_host_ecdsa_key
> +ConditionPathExists=|!/etc/ssh/ssh_host_ed25519_key
>
>  [Service]
>  Environment="SYSCONFDIR=/etc/ssh"
>  EnvironmentFile=-/etc/default/ssh
>  ExecStart=@BASE_BINDIR@/mkdir -p $SYSCONFDIR
> -ExecStart=@BINDIR@/ssh-keygen -q -f ${SYSCONFDIR}/ssh_host_rsa_key -N '' -t rsa
> -ExecStart=@BINDIR@/ssh-keygen -q -f ${SYSCONFDIR}/ssh_host_dsa_key -N '' -t dsa
> -ExecStart=@BINDIR@/ssh-keygen -q -f ${SYSCONFDIR}/ssh_host_ecdsa_key -N '' -t ecdsa
> -ExecStart=@BINDIR@/ssh-keygen -q -f ${SYSCONFDIR}/ssh_host_ed25519_key -N '' -t ed25519
> +ExecStart=@LIBEXECDIR@/sshd-check-key ${SYSCONFDIR}/ssh_host_rsa_key rsa
> +ExecStart=@LIBEXECDIR@/sshd-check-key ${SYSCONFDIR}/ssh_host_dsa_key dsa
> +ExecStart=@LIBEXECDIR@/sshd-check-key ${SYSCONFDIR}/ssh_host_ecdsa_key ecdsa
> +ExecStart=@LIBEXECDIR@/sshd-check-key ${SYSCONFDIR}/ssh_host_ed25519_key ed25519
> +ExecStart=@BASE_BINDIR@/sync
>  Type=oneshot
>  RemainAfterExit=yes
> diff --git a/meta/recipes-connectivity/openssh/openssh_7.5p1.bb b/meta/recipes-connectivity/openssh/openssh_7.5p1.bb
> index 5b96745..ec4b55f 100644
> --- a/meta/recipes-connectivity/openssh/openssh_7.5p1.bb
> +++ b/meta/recipes-connectivity/openssh/openssh_7.5p1.bb
> @@ -25,6 +25,7 @@ SRC_URI = "http://ftp.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-${PV}.tar
>             file://openssh-7.1p1-conditional-compile-des-in-cipher.patch \
>             file://openssh-7.1p1-conditional-compile-des-in-pkcs11.patch \
>             file://fix-potential-signed-overflow-in-pointer-arithmatic.patch \
> +           file://sshd-check-key \
>             "
>
>  PAM_SRC_URI = "file://sshd"
> @@ -124,7 +125,14 @@ do_install_append () {
>         sed -i -e 's, at BASE_BINDIR@,${base_bindir},g' \
>                 -e 's, at SBINDIR@,${sbindir},g' \
>                 -e 's, at BINDIR@,${bindir},g' \
> +               -e 's, at LIBEXECDIR@,${libexecdir}/${BPN},g' \
>                 ${D}${systemd_unitdir}/system/sshd.socket ${D}${systemd_unitdir}/system/*.service
> +
> +       sed -i -e 's, at LIBEXECDIR@,${libexecdir}/${BPN},g' \
> +               -e 's, at BASE_BINDIR@,${base_bindir},g' \
> +               ${D}${sysconfdir}/init.d/sshd
> +
> +       install -D -m 0755 ${WORKDIR}/sshd-check-key ${D}${libexecdir}/${BPN}
>  }
>
>  do_install_ptest () {
> --
> 2.9.4
>

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