#!/bin/sh
#
#  msys2-sshd-setup.sh — configure sshd on MSYS2 and run it as a Windows service
#
#  Please report issues and/or improvements to Sam Hocevar <sam@hocevar.net>
#
#  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
#
#  Gotchas:
#    — the log file will be /var/log/msys2_sshd.log
#    — if you get error “sshd: fatal: seteuid XXX : No such device or address”
#      in the logs, try “passwd -R” (with admin privileges)
#
#  Changelog:
#   27 Jun 2019 — rename service to msys2_sshd to avoid conflicts with Windows OpenSSH
#               — use mkgroup.exe as suggested in the comments
#               — fix a problem with CRLF and grep
#   24 Aug 2015 — run server with -e to redirect logs to /var/log/sshd.log
#

set -e

#
# Configuration
#

PRIV_USER=sshd_server
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


#
# The privileged cyg_server user
#

# Some random password; this is only needed internally by cygrunsrv and
# is limited to 14 characters by Windows (lol)
tmp_pass="$(tr -dc 'a-zA-Z0-9' < /dev/urandom | dd count=14 bs=1 2>/dev/null)"

# Create user
add="$(if ! net user "${PRIV_USER}" >/dev/null; then echo "//add"; fi)"
if ! net user "${PRIV_USER}" "${tmp_pass}" ${add} //fullname:"${PRIV_NAME}" \
              //homedir:"$(cygpath -w ${EMPTY_DIR})" //yes; then
    echo "ERROR: Unable to create Windows user ${PRIV_USER}"
    exit 1
fi

# Add user to the Administrators group if necessary
admingroup="$(mkgroup -l | awk -F: '{if ($2 == "S-1-5-32-544") print $1;}')"
if ! (net localgroup "${admingroup}" | grep -q '^'"${PRIV_USER}"'\>'); then
    if ! net localgroup "${admingroup}" "${PRIV_USER}" //add; then
        echo "ERROR: Unable to add user ${PRIV_USER} to group ${admingroup}"
        exit 1
    fi
fi

# Infinite passwd expiry
passwd -e "${PRIV_USER}"

# set required privileges
for flag in SeAssignPrimaryTokenPrivilege SeCreateTokenPrivilege \
  SeTcbPrivilege SeDenyRemoteInteractiveLogonRight 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 or update /etc/passwd entries
#

touch /etc/passwd
for u in "${PRIV_USER}" "${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
mkgroup.exe -l > /etc/group


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

cygrunsrv -R msys2_sshd || true
cygrunsrv -I msys2_sshd -d "MSYS2 sshd" -p \
          /usr/bin/sshd.exe -a "-D -e" -y tcpip -u "${PRIV_USER}" -w "${tmp_pass}"

# The SSH service should start automatically when Windows is rebooted. You can
# manually restart the service by running `net stop msys2_sshd` + `net start msys2_sshd`
if ! net start msys2_sshd; then
    echo "ERROR: Unable to start msys2_sshd service"
    exit 1
fi