fix(isolation): close the 304, HEAD and trailing-bytes gaps on the read side - #436
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The visibility filter, owner isolation's /system/df filter and the response filter all forwarded a 304 Not Modified untouched. A client that fetched a list or an inspect before a policy tightened, or before any policy existed, could revalidate with If-None-Match or If-Modified-Since and have the daemon confirm the copy it already held, so the body it went on using never passed a filter. The validator behind that copy is the daemon's, computed over the unfiltered body, and every axis that would narrow it is reloadable, so the cached copy and the current policy can differ by an arbitrary amount. The strip goes in the reverse proxy's Rewrite rather than in each of the three layers. That is the one point every proxied request passes through exactly once, it is the last point before the wire, and it makes the guarantee independent of which layers are configured. Doing it per layer would need the three to agree on a path predicate, and the response filter has no request-side hook at all: its coverage is a dispatch table, so any predicate a middleware consulted would go stale the moment that table grew an entry. Rewrite edits ReverseProxy's outbound clone, so the client's request and the access and audit record of what it sent are unchanged. A 304 arriving anyway is refused rather than relayed, matching how each layer already treats a body it cannot walk. Each refusal carries its own reason code (visibility_not_modified_unfilterable, owner_not_modified_unfilterable, and the response filter's existing rejectResponse path) so it does not read as a policy lookup that failed, which is a different investigation. 204 keeps its pass-through: it is not a revalidation and has no stale representation behind it. Pre-existing and theoretical. Neither dockerd nor Podman emits ETag or Last-Modified on these routes, so a conditional request against either is already answered with a full 200 and the strip changes nothing observable. The fail-closed claim in the docs should not rest on an upstream detail this proxy does not control.
…d lists HEAD on a route this proxy constrains on the response was forwarded untouched, so the daemon's Content-Length and ETag reached the client describing the unfiltered body. The length counts the containers and images a name or image pattern hides, and the ETag validates them, which makes a HEAD a cheap fingerprint of exactly what the policy was configured to conceal. It covers /containers/json and /images/json plus both /libpod spellings under the pattern axes, and /system/df under either visibility policy or owner isolation, since that route takes no filters parameter and is scoped entirely on the response. The headers are cleared and the request is still forwarded, rather than the route being refused. The refusals this middleware already has are for endpoints no policy axis can scope on any method: /libpod/system/df and the unscopeable libpod reads carry neither labels nor names, GET is refused there too, and HEAD is refused only so a method-scoped gate cannot forward what GET could not. Here GET is fully scoped and only the HEAD's metadata is not, so a refusal would be a per-method status this package has nowhere else, and neither candidate is true: 405 claims the route rejects the method, and 502 blames the upstream for a decision this proxy made. The rule that does fit is already in the package — the client never receives a representation header describing bytes it did not get, which clearUpstreamRepresentationHeaders enforces for the rewritten bodies and for both fail-closed 502 paths. A HEAD is that rule at zero bytes. Go omits Content-Length for a HEAD when the handler declares none and writes nothing, so the response carries no length rather than a fabricated 0; a test over a real server pins that rather than trusting the recorder. Ownership's HEAD /system/df is fixed alongside visibility's because it is the same leak on the same route. The two layers nest, so a deployment running both had it closed by visibility already, but owner isolation without a visibility policy did not. Routes whose selectors are injected into the upstream request are deliberately untouched: the daemon computes their length over the already-scoped list, so there is nothing there to hide.
The pattern response filter walked the buffered list body element by element and stopped when Decoder.More() went false. That is false both when the array closes and when the input runs out, so the parser never established that the array closed at all, and it never looked at what came after it. A body ending mid-array, or a valid array followed by a second value or by garbage, was rewritten into a well-formed 200 the client read as the complete list. The closing delimiter is now required and any non-whitespace trailing bytes are refused, with the same 502 the non-array case already used. Trailing whitespace still passes. Most truncations did surface already, through the element decode rather than through any check in this parser, so they held by accident of how More() and Decode() interact; trailing bytes were not caught at all. The reasoning is the non-array case's: a body this build cannot account for in full is one whose contents it cannot claim to have checked, so it is not completed on the client's behalf. Elements were always filtered individually, so this was never a confidentiality bypass. What it cost was the documented fail-closed claim, which was narrower than stated. FuzzVisibilityFilter now asserts the refusal itself, with encoding/json's whole-body parse as an oracle against the streaming decoder under test, rather than only bounding output length. That bound could only catch a body that grew, and both gaps here were bodies that were silently completed. Ran clean over 1.6 million executions.
…ditional-and-head # Conflicts: # CHANGELOG.md
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Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe proxy removes conditional request headers before forwarding requests. Response filtering rejects GET and HEAD 304 responses while preserving non-GET/HEAD 304 responses. Visibility and ownership middleware sanitize filtered HEAD representation headers and fail closed on unfilterable 304 responses. Visibility list filtering rejects incomplete JSON arrays and trailing data. Tests and security documentation cover these behaviors. Merge Risk: ⚪ Minimal · up to This change hardens filtered read responses by stripping conditional requests, refusing unsafe GET and HEAD 304 responses, removing unfiltered HEAD metadata, and rejecting malformed filtered arrays. The covered owner-scoped HEAD 304 path now fails closed, with no remaining concrete merge-blocking risk. 🚥 Pre-merge checks | ✅ 2✅ Passed checks (2 passed)
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Filter.ModifyResponse rejected every 304 before the method/status gate,
including on writes. It is the single proxy-wide ReverseProxy.ModifyResponse
(wired in cmd/serve.go), so it also intercepted POST /containers/{id}/start
and POST /containers/{id}/stop, both of which the Docker Engine API
documents as legitimately answering 304 ("container already started" /
"container already stopped") when the container is already in the requested
state. Podman's compat and /libpod routes mirror both, plus its own
POST /libpod/containers/{id}/init ("container already initialized").
Checked the full Engine API spec (moby/moby api/docs, through v1.56) and
Podman's route comments (containers/podman pkg/api/server/register_containers.go):
restart, kill, pause and unpause document no 304 response on either API, so
start/stop/init are the whole documented set today.
Rejecting those turned a correct idempotent no-op into a 502 for
orchestrators and retry loops. Move the 304 check to branch on method: GET
and HEAD keep the existing refusal (a 304 there can only mean cache
revalidation, which StripConditionalRequestHeaders means a daemon cannot
legitimately produce), every other method now passes the 304 through
unchanged.
Checked the visibility and ownership 304 backstops added alongside the
original strip: both are unreachable except under a GET/HEAD gate already
(visibility/middleware.go's Middleware returns early for any other method
before reaching patternFilterWriter; ownership/system_data_usage.go's
serveOwnershipAllowed only routes to filterSystemDataUsageResponse on
http.MethodGet), so neither needed scoping.
Adds table-driven cases for start/stop pass-through (plain, /v1.45/-prefixed,
and /libpod) with every redaction option on, plus an end-to-end proxy test
showing a 304 from POST start reaches the client as 304 through the real
ReverseProxy.ModifyResponse wiring.
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Three read-side gaps closed; Codex's start/stop 304 regression fixed in 7bd48e0 before merge.
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Three read-side gaps closed; Codex's start/stop 304 regression fixed in 7bd48e0 before merge.
…ditional-and-head # Conflicts: # CHANGELOG.md
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Inline comments:
In `@app/internal/ownership/system_data_usage.go`:
- Line 147: In app/internal/ownership/system_data_usage.go:147, update the
owner-scoped HEAD /system/df response flow around
forwardHeadWithoutUpstreamRepresentation to reject an upstream 304 with the
existing owner-specific 502 before WriteHeader; in
app/internal/ownership/conditional_request_test.go:67-92, extend the refusal
test to cover HEAD; in docs/content/docs/security.mdx:347, preserve the existing
documentation claim with no direct change unless needed to reflect the
implemented behavior.
In `@app/internal/visibility/middleware.go`:
- Line 484: Update the response-finalization flow around
interceptingW.statusCode so an upstream http.StatusNotModified uses the existing
errNotModifiedUnfilterable refusal path before w.WriteHeader commits the
filtered HEAD response. Preserve normal status handling for other responses and
add coverage for pattern-filtered lists and /system/df HEAD 304 responses.
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app/internal/ownership/conditional_request_test.goapp/internal/ownership/system_data_usage.goapp/internal/ownership/system_data_usage_test.goapp/internal/proxy/conditional_request_test.goapp/internal/proxy/proxy.goapp/internal/responsefilter/conditional_request.goapp/internal/responsefilter/conditional_request_test.goapp/internal/responsefilter/filter.goapp/internal/visibility/conditional_request_test.goapp/internal/visibility/fuzz_test.goapp/internal/visibility/list_array_termination_test.goapp/internal/visibility/middleware.goapp/internal/visibility/middleware_filter_writer_test.goapp/internal/visibility/system_data_usage.goapp/internal/visibility/system_data_usage_test.godocs/content/docs/security.mdx
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visibility's forwardHeadWithoutUpstreamRepresentation and ownership's helper of the same name forwarded whatever status the upstream sent on a HEAD, including a recorded 304. Their GET twins already refuse a 304 with a fail-closed 502 (visibility_not_modified_unfilterable / owner_not_modified_unfilterable), because a 304 only means the client's cached copy is current under whatever policy produced it, and neither layer can vouch for that on a HEAD any more than on a GET. Both helpers now check the recorded upstream status before forwarding and apply the same refusal the GET path applies, same reason code and logging, instead of relaying the 304. A real daemon can't reach this branch since conditional headers are stripped before the request reaches it, but the backstop is meant to be unconditional on these routes, matching the fail-closed claim in docs/content/docs/security.mdx. Extends the existing 304 refusal tests in both packages with HEAD cases, plus a real-server test per package confirming the 502 body never actually reaches the wire on a HEAD.
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Three read-side gaps closed; Codex's start/stop 304 regression and CodeRabbit's HEAD 304 gap fixed before merge.
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Three read-side gaps closed; Codex's start/stop 304 regression and CodeRabbit's HEAD 304 gap fixed before merge.
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Three read-side gaps from the roadmap (S28, S29, S30), one commit each.
304 bypassed the filters. Visibility, ownership and the response filter all forwarded a 304 untouched, so a client that cached an unfiltered body before a policy change could get it re-confirmed with If-None-Match. Theoretical today (dockerd emits no ETag on these routes), but the fail-closed claim should hold. Fix is in one place: the ReverseProxy Rewrite strips If-None-Match, If-Modified-Since, If-Match, If-Unmodified-Since and If-Range from every upstream request, so the daemon always answers with a full body. The client's own request is untouched, so logs still show what it sent. As a backstop, a 304 that arrives anyway 502s at each layer with its own reason code.
HEAD on filtered lists leaked length and ETag.
HEAD /containers/jsonunder a name_patterns policy passed upstream Content-Length and ETag through, which fingerprints hidden containers. Now the same rule the body paths already follow applies: the client never gets representation headers for bytes it didn't receive. Covers the four pattern-filtered list routes plus /system/df in both visibility and ownership. Selector-injected routes (/networks, /volumes, /services) are untouched because the daemon already computes their length over the scoped list.Array parser accepted trailing bytes.
[{"Id":"a"}]garbagewas accepted and rewritten. The truncation cases in the roadmap item ([,[{) actually already 502'd through Decode failing, so the real gap was only trailing input. The parser now requires the closing]and rejects non-whitespace after it, and FuzzVisibilityFilter asserts refusal directly instead of just bounding output length.security.mdx's "non-success responses pass through unmodified" line was updated since the 304 refusal makes it false.
Changelog
304 Not Modifiedresponses on filteredGETandHEADpaths with502 Bad Gateway.POST304responses for container operations.HEADresponses.HEAD, and304handling.security.mdxwith conditional request,HEAD, and JSON validation behavior.Concerns
304rejection logic.POST304pass-through cannot affect filtered read paths.