1# Security Hardening Controls
2
3This page summarizes Gordon's security-related configuration knobs and the defaults operators should know before exposing an instance.
4
5## Registry upload quotas
6
7Registry blob uploads are bounded by two limits under `[server]`:
8
9```toml
10[server]
11max_blob_chunk_size = "95MB"
12max_blob_size = "1GB"
13```
14
15- `max_blob_chunk_size` limits a single upload chunk.
16- `max_blob_size` limits the cumulative blob/layer upload size.
17- Exceeding either limit returns an OCI-compatible size error and the failed upload is cleaned up.
18
19## Admin logs permission
20
21Container and deploy logs can include environment-derived output. Gordon gates log access behind a dedicated scope:
22
23```bash
24gordon auth token generate --subject ops --scopes "admin:logs:read" --expiry 30d
25```
26
27- `/admin/logs`, app failure diagnostics, and deploy failure logs require `admin:logs:read`.
28- `admin:status:read` does not grant log access.
29- Operation errors returned to `admin:apps:read` callers are stable and log-free. Application diagnostics are a separate field, redacted of the affected service's resolved secret values before storage, and returned only to callers holding `admin:logs:read`. If a declared secret cannot be resolved for redaction, Gordon drops the diagnostics instead of storing unredacted output. Mutation responses never include application output.
30- Process and container log sources remain operator-owned data. Gordon redacts common credential patterns when serving logs through its API, but this is defense in depth rather than proof that arbitrary application output is secret-free. Restrict filesystem, journal, runtime, backup, and `admin:logs:read` access accordingly.
31
32## Volume pruning scope
33
34Volume pruning removes a volume only when Gordon has a durable `released` ownership record, the runtime app/incarnation/service labels agree with that record, and no container mounts it. A `gordon.managed=true` label by itself is not deletion authority; retained, unknown, contradictory, and unrelated volumes survive.
35
36Use `gordon volumes prune --dry-run` before deletion. Do not substitute `docker volume prune` or an equivalent runtime command: runtime-native pruning bypasses Gordon's ownership and retention checks.
37
38Use dedicated admin scopes:
39
40- `admin:volumes:read` for listing volumes.
41- `admin:volumes:write` for prune operations.
42
43## Administrative app bind mounts
44
45App manifests cannot name host paths. A host bind exists only when the operator declares a named policy in `gordon.toml`:
46
47```toml
48[app_mounts.app-logs]
49source = "/srv/gordon/host-logs"
50read_only = true
51allowed_apps = ["metrics-agent"]    # exact, non-empty
52allowed_services = ["web"]          # exact, non-empty
53root = "/srv/gordon"                # optional boundary
54```
55
56The manifest references only the policy name: `[[services.<name>.bind]] name = "app-logs"` with an absolute container `path`.
57
58- `allowed_apps` and `allowed_services` are exact, non-empty allowlists, so least privilege is enforced by construction. There is no wildcard, prefix, or empty-means-all form.
59- `source` is resolved through symlinks and must be a regular file or directory under `root`. When `root` is omitted, the source's parent directory is the boundary. Devices, sockets, FIFOs, and escaping symlinks are refused.
60- Read-only precedence: `read_only` on the policy or `readonly` on the manifest bind forces the mount read-only; a manifest never weakens its policy.
61- Destinations must be absolute, normalized, and outside reserved container paths (`/`, `/proc`, `/sys`, `/dev`, `/boot`, and their children).
62- The policy is re-resolved immediately before every container create, restart, and recovery. Removing a policy or an allowlist entry blocks future deploys; running containers keep their current mounts until redeployed.
63- `gordon serve` reload republishes validated policies atomically. An edit that fails validation is rejected and the previous policies stay live.
64- Gordon never creates, deletes, chowns, backs up, or prunes the host path; ownership, permissions, and backup remain the operator's responsibility.
65
66## Administrative app devices (CDI)
67
68App manifests cannot name host devices. A device grant exists only when the operator declares a named policy in `gordon.toml`:
69
70```toml
71[app_devices.transcode-gpu]
72cdi = ["example.com/gpu=GPU-device-uuid"]
73allowed_apps = ["video"]          # exact, non-empty
74allowed_services = ["transcoder"]  # exact, non-empty
75```
76
77The manifest references only the logical name: `devices = ["transcode-gpu"]`.
78
79- `cdi` holds explicit CDI device IDs. Raw `/dev` paths, unqualified names, and aggregate `=all` selectors are rejected.
80- `allowed_apps` and `allowed_services` are exact, non-empty allowlists, so least privilege is enforced by construction. There is no wildcard, prefix, or empty-means-all form.
81- Gordon resolves logical names to CDI IDs at activation time and encodes them as one native CDI `DeviceRequest`. Revisions persist the logical names, never the host resolution.
82- The grant is re-resolved immediately before every preflight, container create, restart, and recovery. Revoking a grant blocks future deploys while the running service is untouched; changing a mapping never recreates a running container.
83- Device-bearing creates require Podman 5.4+ or Docker 28.3+ with native CDI configured. Older or unrecognized engines fail with a structured `runtime-unsupported` error and never run without devices.
84- Gordon installs no drivers, manages no quotas, and injects no device environment: images carry their own runtime expectations.
85
86### Plain device nodes under rootless Podman
87
88> **Verified by source reading only. Confirm on the host:** create a throwaway container with the same device IDs (`podman run --rm --device example.com/vm=kvm --device example.com/vm=net-tun alpine ls -l /dev/kvm /dev/net/tun`) as the rootless user before the first Gordon deploy.
89
90CDI is not GPU-specific. Any device node can be exposed through a user-level CDI spec, so `/dev/kvm` and `/dev/net/tun` reach a rootless Podman service without raw `/dev` paths in manifests and without any privilege:
91
92```yaml
93# ~/.config/cdi/vm.yaml  (rootless user, mode 0644)
94cdiVersion: "0.6.0"
95kind: example.com/vm
96devices:
97  - name: kvm
98    containerEdits:
99      deviceNodes:
100        - path: /dev/kvm
101  - name: net-tun
102    containerEdits:
103      deviceNodes:
104        - path: /dev/net/tun
105```
106
107```toml
108# ~/.config/containers/containers.conf (the rootless user that runs the Podman API service)
109[engine]
110# Setting cdi_spec_dirs replaces the defaults: keep /etc/cdi and /var/run/cdi if you use them.
111cdi_spec_dirs = ["/etc/cdi", "/var/run/cdi", "/home/<user>/.config/cdi"]
112```
113
114```toml
115# gordon.toml
116[app_devices.my-vm-device]
117cdi = ["example.com/vm=kvm", "example.com/vm=net-tun"]
118allowed_apps = ["myapp"]
119allowed_services = ["worker"]
120```
121
122- **Status: verified by source reading (Podman 5.7.1), not by a live run. Confirm on your host before relying on it.** No Gordon change appeared necessary. Gordon sends the IDs as a native `cdi` `DeviceRequest`; the Podman compat API forwards them to the same CDI injection as `podman run --device <id>`, which reads `cdi_spec_dirs` from the containers.conf of the user running the API service. Restart that service (`systemctl --user restart podman.socket podman.service`) after editing `containers.conf`; edits to the spec files themselves are picked up on the next container create.
123- Under rootless Podman the OCI runtime (crun or runc) cannot `mknod` in a user namespace and falls back to bind-mounting the host device node into the container. The node must therefore be accessible to the rootless user on the host: `/dev/kvm` and `/dev/net/tun` are usually `0666` or group-owned (`kvm`). Supplementary groups do not carry into the user namespace, so prefer a `0666`/ACL-based permission over group membership.
124- CDI device names Gordon accepts match `[A-Za-z0-9][A-Za-z0-9_.-]*` (so `kvm` and `net-tun` are valid; names containing `:` are not).
125- A missing spec dir entry, an unreadable spec, or an unknown device name surfaces as a redacted create failure (`runtime error redacted`); check the Podman service journal for the CDI error.
126
127## Administrative app capabilities
128
129App manifests cannot add Linux capabilities. A grant exists only when the operator declares a named policy in `gordon.toml`:
130
131```toml
132[app_capabilities.vm-net]
133add = ["NET_ADMIN"]
134allowed_apps = ["myapp"]    # exact, non-empty
135allowed_services = ["worker"]     # exact, non-empty
136```
137
138The manifest references only the logical name: `capabilities = ["vm-net"]`.
139
140- `add` holds explicit Linux capability names, written without the `CAP_` prefix. Only this allowed set is accepted: `AUDIT_WRITE`, `CHOWN`, `DAC_OVERRIDE`, `FOWNER`, `FSETID`, `IPC_LOCK`, `KILL`, `MKNOD`, `NET_ADMIN`, `NET_BIND_SERVICE`, `NET_RAW`, `SETFCAP`, `SETGID`, `SETPCAP`, `SETUID`, `SYS_CHROOT`, `SYS_NICE`, `SYS_RESOURCE`. Everything else is rejected when the config loads, including `ALL`, `SYS_ADMIN`, `SYS_PTRACE`, `SYS_MODULE`, `SYS_RAWIO`, `SYS_BOOT`, `SYS_TIME`, `DAC_READ_SEARCH`, `BPF`, `PERFMON`, `MAC_ADMIN`, `MAC_OVERRIDE`, `AUDIT_CONTROL`, and `SYSLOG`. These can reach the host or defeat container confinement; a workload that needs one is not an unprivileged service.
141- **The allowed capabilities are not harmless.** The list only removes capabilities that clearly break confinement; each remaining one still needs a workload-specific assessment before you grant it. In particular: `SETFCAP` lets a process write file capabilities, which is dangerous together with writable binds or volumes shared with another service or the host; `MKNOD` creates device nodes (inert in a user namespace, but a risk if the runtime ever runs without one); `NET_RAW` allows packet spoofing and raw sockets inside the container's network namespace and on any shared network; `SYS_CHROOT`, `SETPCAP`, `KILL`, `DAC_OVERRIDE`, `FOWNER` and `FSETID` widen what a compromised process can do to files and processes it can reach; `NET_ADMIN` controls every interface, route, and firewall rule in the container's network namespace, including a shared network attachment. Grant the smallest set to the narrowest app+service pair.
142- `allowed_apps` and `allowed_services` are exact, non-empty allowlists. There is no wildcard, prefix, or empty-means-all form. Unknown keys inside `[app_capabilities.<name>]` fail closed.
143- Granted capabilities are added on top of Gordon's default set (`CHOWN`, `DAC_OVERRIDE`, `FOWNER`, `SETUID`, `SETGID`, `NET_BIND_SERVICE`). Gordon's `cap_drop = ALL` and `no-new-privileges` stay in force, and containers are never privileged. The runtime guard re-checks the resolved list before every create.
144- Capabilities apply inside the container's own user and network namespaces. Under rootless Podman, `NET_ADMIN` lets the service create TAP devices and nftables rules in its own network namespace, not on the host. Because `no-new-privileges` stays on, a process only holds the added capabilities when it runs as container root (uid 0 in the user namespace, which is an unprivileged host user under rootless Podman); a non-root container user cannot gain them through file capabilities.
145- Gordon resolves logical names at activation time. Revisions persist the logical names, never the resolution. The grant is re-resolved before every preflight, container create, restart, and recovery. Revoking a grant blocks future deploys and restarts while the running service is untouched.
146- **Narrowing a policy is enforced on reuse.** A container keeps the capabilities it was created with, so before Gordon restarts, starts, or health-restarts an existing capability-bearing container it inspects the container's configured `CapAdd` and refuses the operation (`capability-policy-violation`, naming the excess capabilities) when it exceeds Gordon's defaults plus the currently authorized grant. If the container cannot be inspected the operation fails closed. Run `gordon apps deploy` to recreate the service with the narrowed set; the superseded container is retired by the normal replacement. A container missing from the runtime is rebuilt from the pinned revision under the current policy.
147- **Device grants have the same gap, documented rather than fixed.** Narrowing an `[app_devices]` mapping (removing a CDI ID) does not remove the device from an already created container, and a restart or recovery of that container keeps it. Resolution still fails closed for revoked or unknown policies, but Gordon cannot reliably read back the injected CDI devices (Podman's Docker-compatible inspect does not report them), so it cannot verify a narrowed mapping on reuse. After narrowing or revoking a device mapping, run `gordon apps deploy` for the affected service (or stop it) so the container is recreated with the current mapping.
148- Adding or removing a policy name shows as `service/<name>/capabilities` in diffs and recreates the container on the next deploy; reorder-only input is a no-op. Changing what a policy grants does not recreate a running container: the next deploy serves the new resolution.
149
150## External image registries
151
152Docker Hub, `ghcr.io`, `quay.io`, and Gordon's configured registry are always allowed. Add every other registry hostname and non-default port explicitly:
153
154```toml
155[images]
156allowed_registries = ["registry.internal:5000"]
157require_digest = true
158```
159
160- `docker.io` and Docker Hub's canonical pull host `registry-1.docker.io` are equivalent.
161- Other registries are accepted only when their exact hostname+port is configured. Allowlisting does not configure credentials; external resolution and pulls are anonymous unless the runtime already has suitable access.
162- `require_digest = true` requires every image, including Gordon registry images, to use `@sha256:<64 hex chars>`.
163- The allowlist restricts hostnames, not resolved IPs. It cannot prove a DNS hostname is non-private and does not replace firewall or runtime egress controls.
164
165## Smart TCP Raw Fallback
166
167Raw TCP fallback on a `smart_tcp` edge entrypoint is disabled by default. Unknown non-HTTP/non-TLS bytes reach a backend only when the entrypoint explicitly sets `raw_fallback` to a TCP router and the fallback source policy allows the peer.
168
169```toml
170[entrypoints.edge]
171address = ":443"
172protocol = "smart_tcp"
173raw_fallback = "ssh-fallback"
174raw_fallback_trusted_cidrs = ["100.64.0.0/10"]
175```
176
177Use `raw_fallback_trusted_cidrs` for private raw fallback. Public raw fallback requires an explicit acknowledgement:
178
179```toml
180[entrypoints.edge]
181address = ":443"
182protocol = "smart_tcp"
183raw_fallback = "public-raw"
184allow_public_raw_fallback = true
185```
186
187Security behavior:
188
189- PROXY protocol v1 and v2 prefixes are rejected; Gordon does not trust or parse PROXY headers on smart TCP entrypoints.
190- `trusted_cidrs` and `raw_fallback_trusted_cidrs` use the peer socket IP, not `X-Forwarded-For`.
191- HTTP-looking or TLS-looking malformed traffic is rejected and never bypasses to raw fallback.
192- Entry-point-wide `trusted_cidrs` applies before sniffing to all protocols; raw fallback has its own narrower policy for private fallback exposure.
193
194## Docker network isolation
195
196Per-app Docker networks are enabled by default. To block direct external egress from isolated networks, opt into Docker internal networks:
197
198```toml
199[network_isolation]
200enabled = true
201internal = true
202```
203
204`internal = false` remains the compatibility default because some applications need direct egress during startup.
205
206Every app container joins an incarnation-owned private network derived from the app's internal UUID; shared memberships come only from explicit `[[network.shared]]` declarations, and memory/CPU/PID limits apply on every create and recovery path.
207
208## Readiness helper containers
209
210Probing an internal HTTP port uses one bounded helper container per readiness attempt, removed immediately after. Gordon force-removes the helper under an independent cleanup context, including on failure and timeout. There is no operator configuration for the helper; its image and limits are fixed.
211
212- The helper image is digest-pinned and multi-arch: `alpine@sha256:d9e853e87e55526f6b2917df91a2115c36dd7c696a35be12163d44e6e2a4b6bc`. The image must be pre-provisioned and available offline on the target host, because the probe never pulls.
213- The helper attaches only to the target app's private network. It never joins a shared network or a host network.
214- It never publishes a host port and has no mounts, volumes, secrets, environment, or runtime socket.
215- It runs non-root (uid/gid `65534`) with a read-only root filesystem, all capabilities dropped, `no-new-privileges`, and bounded CPU, memory, and PIDs.
216- It targets the exact inspected container IP on that network, never a service alias, and revalidates the container's execution start before trusting the result; a restarted generation is discarded.
217- A target that listens only on its own loopback fails readiness.
218- Helpers left behind by an abrupt daemon or host stop are reclaimed by the next probe once they are older than ten minutes; a live session is never touched.
219
220## Registry exposure
221
222- With `auth.enabled = true`, registry requests are authenticated and repository-scoped; the public proxy forwards registry domains to the internal registry.
223- With `auth.enabled = false`, the registry is local-only: the public proxy refuses registry-domain requests, and the registry handler accepts only direct loopback connections carrying the instance credentials.
224- Registry requests are parsed once into a validated operation used by both authorization and dispatch, so the repository a token is checked against is exactly the repository served.
225- Blob and upload access is repository-scoped: an upload UUID is usable only by the repository that started it, and a blob is served only to a repository that completed an upload of that digest.
226
227## Container runtime profile
228
229```toml
230[containers]
231security_profile = "compat" # or "strict"
232```
233
234- `compat` preserves broad image compatibility while retaining `no-new-privileges` and default capability restrictions.
235- `strict` enables a read-only root filesystem, drops all capabilities, and only adds `NET_BIND_SERVICE`.
236
237Use `strict` for images designed to write only to mounted volumes and run without extra Linux capabilities.
238
239## Runtime guard
240
241Every app container config passes a final guard right before the runtime creates the container. Bind checks also run at deploy preflight and before every restart or recovery of an existing container. A refused config creates or starts no container: the operation fails and its preflight or service step error contains `runtime guard violation`. The guard refuses:
242
243- network mode `host`, `container:<id>`, or `ns:<path>`;
244- a volume name containing `/` or `\`, which the runtime would read as a host path;
245- a bind whose host source is equal to, under, or a parent of a protected path, compared both as written and after resolving symlinks.
246
247Protected paths:
248
249- the data directory and the loaded config file;
250- files and directories set in the config: `server.tls_key_file` and the backup `storage_dir` values;
251- runtime sockets: `/var/run/docker.sock`, `/run/docker.sock`, `/run/podman/podman.sock`, `$XDG_RUNTIME_DIR/docker.sock`, `$XDG_RUNTIME_DIR/podman/podman.sock`, the `unix://` path of `DOCKER_HOST`, and the `server.runtime` socket;
252- rootless runtime storage and config: `~/.local/share/containers`, `~/.local/share/docker`, `${XDG_CONFIG_HOME:-~/.config}/containers`, and `~/.docker`;
253- the systemd user units: `${XDG_CONFIG_HOME:-~/.config}/systemd/user`;
254- Gordon runtime credentials: `$XDG_RUNTIME_DIR/gordon`, `~/.gordon/run`, and `$GORDON_CLOUDFLARE_API_TOKEN_FILE`;
255- key stores: `$GNUPGHOME`, `~/.gnupg`, `$PASSWORD_STORE_DIR`, `~/.password-store`, `$SOPS_AGE_KEY_FILE`, and `${XDG_CONFIG_HOME:-~/.config}/sops/age`.
256
257A protected path that does not exist yet is also protected in its symlink-resolved form, based on its closest existing parent. Backup directories are protected: a backup app cannot bind them, even read-only.
258
259Gordon's enabled file logs (the Gordon log file's directory, the access log's directory, and `logging.container_logs.dir`) can be bound read-only so a log shipper can read them. Under the data directory this applies only at or under `<data_dir>/logs`; outside it, only when the directory neither is, contains, nor lies under another protected path. A writable bind on them is refused. When a log directory does not qualify, for example a log file directly in `$HOME`, the log file itself stays protected and no read-only exception applies.
260
261The only other exception is Gordon's own read-only secret file mount: `<data_dir>/secrets-run/<app>/<container>/<KEY>` at `/run/secrets/<KEY>`. A refused `[app_mounts]` policy fails before the running generation is replaced or restarted. Point the policy `source` outside every protected path.
262
263## Process memory protection
264
265On Linux, `gordon serve` marks itself non-dumpable (`PR_SET_DUMPABLE=0`) as its first step, before loading its config file or any backend secret. Other processes of the same user can no longer read its `/proc/<pid>/environ`, `mem`, or file descriptors, attach with ptrace, or get a core dump. Startup fails if the flag cannot be set.
266
267Limits:
268
269- Secrets passed as environment variables, such as `GORDON_AUTH_TOKEN_SECRET`, are readable for the short time between process start and that first step. Prefer a secrets backend.
270- Helper processes (`pass`, `gpg`, `sops`, `journalctl`) are dumpable again after `exec`; secret tools hold the values they decrypt while they run. Gordon starts them without its `GORDON_*` variables.
271- Root, or a process of the same user that can replace the Gordon binary or its systemd unit, is not stopped.
272
273## Hardened systemd user unit
274
275Add these directives to the `[Service]` section of the [user unit](../installation.md#user-service-recommended-for-rootless):
276
277```ini
278[Service]
279NoNewPrivileges=yes
280UMask=0077
281LockPersonality=yes
282RestrictSUIDSGID=yes
283RestrictRealtime=yes
284SystemCallArchitectures=native
285```
286
287Apply and check:
288
289```bash
290systemctl --user daemon-reload
291systemctl --user restart gordon
292systemctl --user status gordon
293systemd-analyze --user security gordon.service
294```
295
296## Credential scoping
297
298- **Cloudflare DNS-01 token**: grant only `Zone:Read` and `DNS:Edit`, limited to the zones Gordon serves. A leaked token can issue certificates for, and take over, every hostname in those zones. See [Server](./server.md).
299- **Registry push tokens**: issue one token per repository and pipeline instead of a global one:
300
301  ```bash
302  gordon auth token generate --subject ci-blog --scopes push --repo blog
303  ```
304
305## Protection boundary
306
307Gordon v3 protects against:
308
309- file-delivered secret values showing up in container env, `docker inspect`, or `/proc/1/environ`;
310- app configs that mount the runtime socket, Gordon data, config, credentials, or key stores, or that join the host or another container's namespaces;
311- same-user processes reading the Gordon process's memory or environment through `/proc`, within the limits above.
312
313Gordon v3 does not protect against:
314
315- a compromised Gordon process, proxy, or registry: they run as the same user that owns the runtime socket and `pass`;
316- a malicious image deployed for an app: it receives that app's secrets;
317- root on the host.
318
319## Related
320
321- [Auth](./auth.md)
322- [Secrets](./secrets.md)
323- [Images](./images.md)
324- [Network Isolation](./network-isolation.md)
325- [Volumes](./volumes.md)
326- [Reference](./reference.md)