Configure sshd on MSYS2 and run it as a Windows service

configure_sshd.sh

#!/bin/sh
#
#  sshd setup script for gRPC Jenkins windows worker.
#
#  Prerequisites:
#    — MSYS2 itself: http://sourceforge.net/projects/msys2/
#    — admin tools: pacman -S openssh cygrunsrv mingw-w64-x86_64-editrights
#
#  This script is a cleaned up and improved version of the procedure initially
#  found at https://ghc.haskell.org/trac/ghc/wiki/Building/Windows/SSHD
#
#  Changelog:
#   24 Aug 2015 — run server with -e to redirect logs to /var/log/sshd.log
#

set -e

#
# Configuration
#
PRIV_USER_PASSWORD="$1"

PRIV_USER=jenkins  # The script expects this user to already exist and to be admin.
PRIV_NAME="Privileged user for sshd"
UNPRIV_USER=sshd # DO NOT CHANGE; this username is hardcoded in the openssh code
UNPRIV_NAME="Privilege separation user for sshd"

EMPTY_DIR=/var/empty


#
# Check installation sanity
#

if ! /mingw64/bin/editrights -h >/dev/null; then
    echo "ERROR: Missing 'editrights'. Try: pacman -S mingw-w64-x86_64-editrights."
    exit 1
fi

if ! cygrunsrv -v >/dev/null; then
    echo "ERROR: Missing 'cygrunsrv'. Try: pacman -S cygrunsrv."
    exit 1
fi

if ! ssh-keygen -A; then
    echo "ERROR: Missing 'ssh-keygen'. Try: pacman -S openssh."
    exit 1
fi

# set required privileges
for flag in SeAssignPrimaryTokenPrivilege SeCreateTokenPrivilege \
  SeTcbPrivilege SeServiceLogonRight; do
    if ! /mingw64/bin/editrights -a "${flag}" -u "${PRIV_USER}"; then
        echo "ERROR: Unable to give ${flag} rights to user ${PRIV_USER}"
        exit 1
    fi
done


#
# The unprivileged sshd user (for privilege separation)
#

add="$(if ! net user "${UNPRIV_USER}" >/dev/null; then echo "//add"; fi)"
if ! net user "${UNPRIV_USER}" ${add} //fullname:"${UNPRIV_NAME}" \
              //homedir:"$(cygpath -w ${EMPTY_DIR})" //active:no; then
    echo "ERROR: Unable to create Windows user ${PRIV_USER}"
    exit 1
fi

# Add ForceCommand to ensure that all env vars will be available
echo "ForceCommand /home/jenkins/ssh_command.sh" >> /etc/ssh/sshd_config

#
# Add or update /etc/passwd entries
#

touch /etc/passwd
for u in "${UNPRIV_USER}"; do
    sed -i -e '/^'"${u}"':/d' /etc/passwd
    SED='/^'"${u}"':/s?^\(\([^:]*:\)\{5\}\).*?\1'"${EMPTY_DIR}"':/bin/false?p'
    mkpasswd -l -u "${u}" | sed -e 's/^[^:]*+//' | sed -ne "${SED}" \
             >> /etc/passwd
done


#
# Finally, register service with cygrunsrv and start it
#

cygrunsrv -R sshd || true
cygrunsrv -I sshd -d "MSYS2 sshd" -p \
          /usr/bin/sshd.exe -a "-D -e" -y tcpip -u "${PRIV_USER}" -w "${PRIV_USER_PASSWORD}"

# The SSH service should start automatically when Windows is rebooted. You can
# manually restart the service by running `net stop sshd` + `net start sshd`
if ! net start sshd; then
    echo "ERROR: Unable to start sshd service"
    exit 1
fi

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