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swarm-bao: give each hive-cert consumer its own bao identity

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Four units read one path each out of the store, and all four logged in
holding `deploy.bao.clientCertFile` — the hive's own leaf. Bao identifies
a principal by the subject of the certificate it presents, so four
readers behind one certificate were ONE principal, and the only grant
expressible was the union of what the four need: read on
`swarm/agents/*`, `swarm/hives/<hive>/*` and `swarm/services/*`. The unit
fetching Grafana's OIDC client secret could fetch every agent credential
in the swarm; the one fetching this hive's matrix token could fetch
Grafana's. Least privilege was not misconfigured here, it was
unrepresentable.

Each now holds a leaf, a cert-auth role and a policy of its own, and each
policy is the single `secret/data/…` path that unit's own script names —
spelled to the leaf, not to a prefix, the way matrix-ctl's already is.
Following the four exemplars in-tree rather than building a mechanism:
`signLeaf` mints the leaves, `swarm-bao.nix` writes the roles from the
bootstrap token, the consumers name their own pair.

Two of the four are written PER HIVE and two are not, which is the shape
of the paths rather than a preference. A matrix appservice token and a
queue credential live under `swarm/hives/<name>/` and every hive runs a
reader for its own, so one role for all of them would have to be granted
`hives/*` — letting one hive read another's, a reach no hive has today.
An OIDC client secret lives under `swarm/services/<client-id>/` and a
swarm registers each exactly once, so one role each is enough. The
per-hive subjects are `<prefix>-<hive>` and swarm.nix reserves every
composed spelling as a hive name, so a hive cannot be named into another
hive's role.

The shared leaf stays: hive-c0re still passes it into its container, the
`bao` CLI wrapper still defaults to it, and the three
`glue-*-bao-identity.nix` files derive the PKI directory from it.

module-eval-bao-grants gains a negative arm per principal — each pins the
three stanzas the hive's leaf carried and the two wildcards a later
widening would reach for, so a policy that grows fails here rather than
in a store. Plus the consuming side: repointing a unit back at the hive's
leaf would evaluate, deploy and log in, and silently restore the union.

A hive that reads a store on another machine now places one leaf per
principal instead of one shared by four. That cost is the point, and
docs/swarm/secrets.md lists the pairs.
This commit is contained in:
atlas 2026-09-21 23:44:59 +02:00 • committed by mara
commit f1445b4c8b
14 changed files with 859 additions and 43 deletions
Download patch file Download diff file Expand all files Collapse all files

48
nix/host-modules/glue-bao-tls.nix
View file

@ -84,6 +84,25 @@ in
clientCertFile = lib.mkDefault "${pkiDir}/client.pem";
clientKeyFile = lib.mkDefault "${pkiDir}/client-key.pem";
serverCaFile = lib.mkDefault "${pkiDir}/ca.pem";
# 🩸 Four readers that used to present `client.pem` above, each now
# pointed at a leaf of its own. The leaf is what bao sees, so this pairing
# is the whole of what turns "one principal with the union of four grants"
# into four principals with one grant each — see ./swarm-bao.nix's
# `perHiveReaders` block for the grants themselves.
#
# Defaulted here rather than in four `glue-<consumer>-bao-identity.nix`
# files: those exist where the consumer is a CONTAINER with a
# `deploy.<service>.*` namespace of its own to point at. These four are
# host units reading the store, which is the pairing this file already is.
matrixTokenClientCertFile = lib.mkDefault "${pkiDir}/matrix-token.pem";
matrixTokenClientKeyFile = lib.mkDefault "${pkiDir}/matrix-token-key.pem";
queueAgentClientCertFile = lib.mkDefault "${pkiDir}/queue-agent.pem";
queueAgentClientKeyFile = lib.mkDefault "${pkiDir}/queue-agent-key.pem";
grafanaOidcClientCertFile = lib.mkDefault "${pkiDir}/grafana-oidc.pem";
grafanaOidcClientKeyFile = lib.mkDefault "${pkiDir}/grafana-oidc-key.pem";
otelOidcClientCertFile = lib.mkDefault "${pkiDir}/otel-oidc.pem";
otelOidcClientKeyFile = lib.mkDefault "${pkiDir}/otel-oidc-key.pem";
};
# Idempotent on ABSENCE, never on content. Re-issuing the CA invalidates
@ -160,6 +179,35 @@ in
# container an identity instead of lending it the hive's.
[ -s ${pkiDir}/matrix-ctl.pem ] || ${signLeaf} ${pkiDir} matrix-ctl \
${lib.escapeShellArg deployCfg.bao.matrixCtlCommonName} "" clientAuth
# 🩸 The four readers that used to present `client.pem` above. Each
# carries its own subject, which is the entire mechanism: bao matches a
# cert-auth role on the CN, so four units sharing one leaf were one
# principal holding the union of four grants, and the union included
# every agent credential in the swarm.
#
# ⚠️ The first two carry THIS hive's name in the subject, unlike the
# three service leaves above. Their grants name one hive's path, because
# a matrix token and a queue credential live under `swarm/hives/<name>/`
# and every hive runs a reader for its own; ./swarm-bao.nix writes one
# role per hive in the swarm directory to match. The two OIDC readers
# need no such segment — a client is registered once per swarm.
#
# Minted whether or not the consumer runs here, for the reason the three
# leaves above give: on a hive that does not run the store this is the
# file an operator copies, and a leaf that only appears where its
# consumer does is one nobody can copy from anywhere.
[ -s ${pkiDir}/matrix-token.pem ] || ${signLeaf} ${pkiDir} matrix-token \
${lib.escapeShellArg "${deployCfg.bao.matrixTokenCommonNamePrefix}-${clientCn}"} "" clientAuth
[ -s ${pkiDir}/queue-agent.pem ] || ${signLeaf} ${pkiDir} queue-agent \
${lib.escapeShellArg "${deployCfg.bao.queueAgentCommonNamePrefix}-${clientCn}"} "" clientAuth
[ -s ${pkiDir}/grafana-oidc.pem ] || ${signLeaf} ${pkiDir} grafana-oidc \
${lib.escapeShellArg deployCfg.bao.grafanaOidcCommonName} "" clientAuth
[ -s ${pkiDir}/otel-oidc.pem ] || ${signLeaf} ${pkiDir} otel-oidc \
${lib.escapeShellArg deployCfg.bao.otelOidcCommonName} "" clientAuth
'';
};
};