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fix(minimald): name the userns restriction in session attach spawn errors - #2119
norrietaylor merged 8 commits into
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On a userns-restricted host (stock Ubuntu 24.04+, ApparmorUnconfined or userns Disabled), the session sandbox child dies writing its uid map and the client's attach fails with a bare 'session host exited before its channel could attach'. The daemon's startup probe already diagnosed the restriction and its fix, but only logged them. Thread that diagnosis from the probe into the config the session actors build on, and fold it into the spawn-failed error, so the error a client sees names the restriction and the fix instead of a symptom that explains nothing. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Merge Risk: 🔵 Low · up to On a restricted host, an unrelated launch failure may also display user-namespace remediation. The original error remains visible, so the risk is bounded to troubleshooting confusion. Pre-merge checks |
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| Check name | Status | Explanation |
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| Title check |  |
The title clearly identifies the minimald change and the user-namespace restriction diagnosis added to session attach spawn errors. |
| Description check | |
The description provides a detailed summary and testing results, including known pre-existing test failures and targeted test coverage. It does not use the template headings or include the checklist, … |
| Docstring Coverage | |
Docstring coverage is 84.21% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 7 files. |
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A rabbit checks the launch-time clue
A remedy points to the daemon too
The error keeps its kind and name
A hint joins in when checks explain
Then hops away, its work complete.final
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Actionable comments posted: 1
- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @crates/minimald/src/session.rs:
- Around line 4680-4684: Update the error mapping after HostHandle::attach so
HostAttachError::Timeout becomes AttachError::SessionBusy, preserving the
retryable busy outcome; use the spawn diagnostic only for
HostAttachError::Closed.
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📒 Files selected for processing (6)
crates/minimald/src/main.rscrates/minimald/src/server.rscrates/minimald/src/session.rscrates/minimald/src/session/tests.rscrates/minimald/src/sessions.rscrates/minimald/src/test_harness.rs
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The startup probe's verdict went stale once a sysctl changed under a running daemon (the host-setup doc's sysctl -w fix needs no restart), so the attach error could name a lifted restriction or miss a new one. Re-probe at failure time instead, share the fix text with the startup warning through userns_restriction_fix, and drop the Config -> Manager -> Session plumbing the cached hint needed.
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/review |
Append the userns diagnosis to a launch_host failure as well as a failed first attach, keeping the launch error's kind, and give the attach hint only to a host whose loop closed, never to a timed-out live one.
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# Conflicts: # crates/minimald/src/session.rs
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2 similar comments
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This PR has merge conflicts with its base branch ( Conflicted files:
Reason it's not trivial: the conflict is in Rust source — both sides rewrote the same userns startup-warning block differently (the PR's Recommended action: rebase or merge manually, then remove the
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# Conflicts: # crates/minimald/src/main.rs
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Routing-Key: inbox-route/I_kwDOSUhdos8AAAABWKn5sQ
On a host that restricts unprivileged user namespaces (stock Ubuntu 24.04+ with
kernel.apparmor_restrict_unprivileged_userns=1, oruser.max_user_namespaces=0), the session sandbox child dies writing its uid map and the client's attach fails with a baresession host exited before its channel could attach— a symptom that names neither the restriction nor the fix. The daemon's startup probe (sandbox2::user_namespaces_restriction()) already computed both, but only logged them.This folds that diagnosis into the spawn-failed attach error via a new
spawn_failed_errorhelper. The restriction is re-probed when the attach fails (userns_spawn_hint), not cached from startup: the sysctls take effect live (the host-setup doc'ssysctl -wfix needs no daemon restart), so a startup verdict could name a lifted restriction or miss a new one. The fix text has one source: sandbox2'sUsernsRestriction::remedy(min finalize-install, thenmin stop), which the create gate (NET-141) also prints.minimald::userns_restriction_fixrenders it for the startup warning and the attach error. The create gate refuses a new session up front on a restricted host; this hint covers every later host launch, which still fails at attach when the restriction arrives after the session was created or the gate is switched off (MINIMALD_USERNS_GATE=off). A launch that fails outright carries the same hint, labelled as the likely cause, and a host that is alive but did not accept its channel in time reports busy with no hint. On a restricted host the client now sees the restriction and the one-time fix inline in the attach error; on unrestricted, root, or off-Linux hosts the message is byte-unchanged. The client crate is untouched: the SSH channel relays daemon error text verbatim, so enriching the daemon-side error is the complete client-visible fix. Root daemons are naturally exempt — the probe returns no restriction for euid 0.Precedent: the restriction diagnosis (informed by #610) and the attach-error plumbing path (informed by #383).
Verification
cargo fmt --all --check— cleancargo clippy --workspace --all-targets --locked -- -D warnings— cleancargo test --locked -p minimald— 915 passed; 12 failures innet::switch/connection/rpcnetns-flavored tests are pre-existing in this sandbox (verified identical on pristinemainviagit stash; they pass in isolation — the runner itself is userns-restricted). The changed code's targeted run — the newspawn_failed_errorunit tests (both arms: bare symptom preserved without a hint; restriction + fix carried with one) plus the fullsession::module — passes 119/119.Summary by CodeRabbit