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review: harden flaps socket grant (symlink guard, verified outcome, precise scope note)

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Address sol-reviewer findings: route the mutation through the existing
refuse_symlinked_path helper (consistency with the script's CWE-59
protections), only print success when both chgrp and chmod actually
succeeded (warn otherwise instead of a false-positive boot log), fix the
lifecycle wording (this hook runs after the supervision tree is up,
before user services), and state the widening scope precisely: the whole
local Machines API becomes group-writable, accepted because the agent
already runs arbitrary user code as the same principal.
This commit is contained in:
Ben Barclay
2026-08-21 07:33:49 +10:00
parent ab0e1b860f
commit c3533b3abd
1 changed files with 14 additions and 7 deletions
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21
docker/stage2-hook.sh
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@@ -476,14 +476,21 @@ fi
# (gateway/scale_to_zero.py suspend_self) must POST to it, but the gateway runs
# as the unprivileged `hermes` user — without this it gets EACCES on every
# suspend attempt and the machine can never sleep (fail-awake; verified live on
# staging 2026-08-20: "flaps suspend request failed: [Errno 13]"). stage2 runs
# as root before the supervision tree starts, so grant group access here.
# Group-write is the minimal widening: the socket stays root-owned and
# non-hermes users gain nothing. No-op off Fly (socket absent).
# staging 2026-08-20: "flaps suspend request failed: [Errno 13]"). This hook
# runs as root before user services (the gateway) start, so grant group access
# here. Scope note: group-write exposes the WHOLE local Machines API to the
# hermes group (any group member could e.g. stop/suspend this machine), not
# just the suspend endpoint — accepted because the agent already executes
# arbitrary user code as that same principal and the socket only controls THIS
# machine. No-op off Fly (socket absent).
if [ -S /.fly/api ]; then
chgrp hermes /.fly/api 2>/dev/null || true
chmod g+w /.fly/api 2>/dev/null || true
echo "[stage2] Granted hermes group access to the Fly Machines API socket"
if refuse_symlinked_path "chgrp/chmod" /.fly/api; then
:
elif chgrp hermes /.fly/api 2>/dev/null && chmod g+w /.fly/api 2>/dev/null; then
echo "[stage2] Granted hermes group access to the Fly Machines API socket"
else
echo "[stage2] Warning: could not grant group access to /.fly/api — scale-to-zero self-suspend will fail EACCES (fail-awake)"
fi
fi
# --- Migrate persisted config schema ---