# The readiness probe (isolated-exec design §8.5): a oneshot under the SAME
# namespace text as the tenant templates (the test pins the block byte for
# byte), run by carlos-instance-control at its start and every five
# minutes. From inside it asserts what a tenant would see and prints a
# verdict; the unit's StandardOutput=truncate: lands it where the control
# service reads it. It exits 0 whatever the verdict: the verdict is the
# output. Its instance directory is _probe, a name no host can have; the
# tmpfiles lines create it.
[Unit]
Description=carlos instance isolation probe
Requires=data-instances.mount run-carlos-instances.mount
After=data-instances.mount run-carlos-instances.mount

[Service]
Type=oneshot
ExecStart=/opt/carlos/carlos instance-probe
User=carlos
Group=carlos
Slice=carlos-instances.slice
StandardOutput=truncate:/run/carlos-control/probe.out
StandardError=journal
TimeoutStartSec=30
# The instance's own two directories, the only writable data paths.
BindPaths=/data/instances/_probe /run/carlos/instances/_probe
ReadWritePaths=/data/instances/_probe /run/carlos/instances/_probe
# The same two binds the instance templates make (#214 item 2), for the
# name _probe: /opt/carlos/live/_probe is a link to ../app, and
# /opt/carlos/app is whatever the source link points at, here the
# platform binary standing in for a build. The control service writes
# both sources before every probe run.
BindReadOnlyPaths=/run/carlos-control/exe/_probe/app:/opt/carlos/app /run/carlos-control/exe/_probe/live:/opt/carlos/live

# --- the namespace (titogo@.service, 2026-07-31 design, on systemd 257) ---
ProtectSystem=strict
TemporaryFileSystem=/data:ro
TemporaryFileSystem=/run/carlos:ro
# Every other tree a carlos-uid unit writes on the box is hidden the same
# way (codex R9-2): the restore drills' cache under /var/cache, and
# /var/lib as a class. An instance needs nothing from either.
TemporaryFileSystem=/var/cache:ro
TemporaryFileSystem=/var/lib:ro
# The version store holds every app's build on the box, world-readable so
# a unit can exec its own (#214 item 2). An instance sees none of it: an
# empty /opt/carlos with the platform binary that ExecStart= and
# ExecStopPost= run put back, and, outside this block because it is per
# instance, its own build at /opt/carlos/live/<host>.
TemporaryFileSystem=/opt/carlos:ro
BindReadOnlyPaths=/opt/carlos/carlos
# Root-written credentials a carlos-GROUP process may read live here:
# /etc/carlos/relay-masters is root:carlos 0640 for carlos-relay.service,
# and an instance's Group=carlos would read it too (codex R10-1). An
# instance gets its configuration through its launch file and needs
# nothing from /etc/carlos. /run/carlos-control is the root control
# service's socket directory (design §5.2): hiding it here too means a
# connect from inside any instance's namespace is impossible outright,
# not merely refused by the peer check on the far end (final review,
# plan 2, item 3).
InaccessiblePaths=/etc/carlos /run/carlos-control
ProtectHome=yes
PrivateTmp=yes
PrivateDevices=yes
# PrivateDevices= bind-mounts the HOST's /dev/shm into the private /dev,
# and every instance is uid carlos, so a sibling's shared memory would be
# one open away. Each unit gets its own, charged to its own cgroup.
TemporaryFileSystem=/dev/shm:mode=1777,nosuid,nodev
# POSIX message queues and SysV IPC belong to an IPC namespace, and every
# instance is uid carlos, so a sibling's queue would be one mq_open away
# (#178). PrivateIPC= gives each unit its own namespace, and mq_open()
# goes through that namespace's own internal mount. PrivateDevices=
# carries the host's /dev/mqueue into the private /dev the way it carries
# /dev/shm, and that mount would still list and open the host namespace's
# queues, so it is replaced the same way.
PrivateIPC=yes
TemporaryFileSystem=/dev/mqueue:ro
# /sys/fs/cgroup read-only: the edge's delegated subtree is carlos-owned,
# and its cgroup.kill / cgroup.freeze would otherwise be one write away
# for a same-uid tenant (codex R9-1).
ProtectControlGroups=yes
ProtectProc=invisible
ProcSubset=pid
PrivatePIDs=yes
RestrictNamespaces=yes
NoNewPrivileges=yes
CapabilityBoundingSet=
RestrictAddressFamilies=AF_INET AF_INET6 AF_UNIX
# Abstract unix sockets live in the network namespace, which instances
# share with the box because they need outbound TCP, and the line above
# cannot tell them from path sockets (#178). The trampoline scopes them
# with Landlock before it execs the app (instanceexec.ScopeAbstractUnix):
# an instance can connect only to abstract sockets its own processes
# bound. A sibling can still bind a name first; that is a refusal of
# service, never a connection.
#
# Egress (#214 item 3): the internet, and nothing on the box or private.
# Loopback is where the console and other tenants' addr upstreams listen;
# RFC 1918, ULA, link-local and CGNAT are the VPC, other boxes and the
# cloud's internal services. IMDS stays named so the property is
# greppable. A cgroup filter: it drops in both directions for every
# socket the unit opens. The one thing an instance needs from these
# ranges is the box's DNS resolver, so the control service re-opens
# exactly the nameservers the instance sees with IPAddressAllow= on
# carlos-instances.slice (an allow wins, and a slice's lists reach every
# unit below it). The probe checks both halves.
IPAddressDeny=localhost multicast 0.0.0.0/8 10.0.0.0/8 100.64.0.0/10 169.254.0.0/16 169.254.169.254/32 172.16.0.0/12 192.0.0.0/24 192.168.0.0/16 198.18.0.0/15 240.0.0.0/4 64:ff9b::/96 fc00::/7 fd00:ec2::254/128 fe80::/10 fec0::/10
# An allow opens an address both ways and on every port, so a loopback
# resolver can never be opened: a tenant could bind systemd-resolved's
# 127.0.0.53 itself and reach every listener bound to all addresses
# through it. Where resolved runs, instances resolve through its
# upstreams instead, and the control service opens those. The "-" makes
# this a no-op on a box without resolved.
BindReadOnlyPaths=-/run/systemd/resolve/resolv.conf:/etc/resolv.conf
ProtectKernelTunables=yes
ProtectKernelModules=yes
ProtectKernelLogs=yes
ProtectClock=yes
ProtectHostname=yes
RemoveIPC=yes
LockPersonality=yes
RestrictRealtime=yes
# No RestrictSUIDSGID=: systemd cannot read the mode inside openat2's
# open_how, so it refuses openat2 outright (ENOSYS), and every instancefs
# open in here is an openat2 (#126, first roll; systemd 257). What it
# guarded is covered: with no capabilities an instance can only make a
# set-id file owned by carlos, which gains nothing for another carlos
# process, NoNewPrivileges= voids it in here, and no other uid can reach
# one (the tenant trees are nosuid, PrivateTmp's sit under a root 0700
# directory).
MemoryDenyWriteExecute=yes
SystemCallArchitectures=native

# --- per-service resources; the tier lives on the host slice (§4.3) ---
TasksMax=64
MemoryMax=64M
# Read back by the probe from its own cgroup (#214 item 1): proof that CPU
# and IO settings take under carlos-instances.slice, where the control
# service sets each host slice's from its tier.
CPUQuota=50%
CPUWeight=50
IOWeight=50