Make dosh terminal sessions survive a dosh-server restart
(crash/upgrade/systemctl restart): a reattaching client lands on the
SAME shell with screen state intact, instead of a fresh one.
Design: when persist_sessions is on (new config, default true) each
terminal session's shell runs in a small detached per-session holder
process (the dosh-server binary re-exec'd as `dosh-server hold`). The
holder double-forks + setsid into its own session, opens the PTY, spawns
the shell as ITS child, and serves the PTY master fd over a per-session
Unix socket via SCM_RIGHTS. The server adopts that fd to build a PtyHandle
that DETACHES (does not kill the shell) on drop, so a server exit leaves
holder + shell alive. On startup the server scans the runtime dir under
sessions_dir/run, reconnects to each live holder, receives the master fd
again, restores the persisted vt100 screen, and rebuilds the Session.
Screen/scrollback (server-memory only) is mirrored to disk atomically:
byte-throttled on the output hot path plus a 2s periodic flush, and
restored on re-adoption so reattach repaints. Truly-abandoned persistent
sessions are still reaped per the existing grace logic by asking the
holder to shut down. Anything in the persistent path failing degrades
gracefully to the original in-process shell.
PtyHandle gains an Owned (kill-on-drop, unchanged default) vs Adopted
(detach-on-drop) backing; resize on an adopted master uses TIOCSWINSZ.
No wire-format change, so protocol::VERSION stays 3. New deps: libc
(direct). New config: persist_sessions (default true); existing
integration tests pin it false to keep exercising the non-persistent
path unchanged.
Adds tests/integration_smoke.rs::session_survives_server_restart_same_
shell_and_screen: attaches, sets `cd /tmp; export MARK=...`, paints a
screen marker, KILLs the server, restarts it on the same config, reattaches
and asserts same shell pid + MARK + PWD + restored screen. Plus persist.rs
unit tests (name round-trip, screen save/load, dead-holder scan cleanup,
SCM_RIGHTS fd round-trip). cargo fmt --check and cargo test green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Item 3: SSH-agent forwarding, double-gated (client -A/forward_agent AND server
allow_agent_forwarding) and off by default on both ends.
Wire: new ForwardingKind::Agent (appended, existing bincode discriminants
unchanged). Bumped protocol VERSION 2 -> 3 so a pre-agent peer answers with a
clear version-mismatch reject instead of a deserialize error.
Client: -A / --forward-agent flag; requires local SSH_AUTH_SOCK. Requests an
Agent forwarding during native auth (agent forwarding requires native auth) and,
on a server-initiated StreamOpen carrying the reserved @dosh-agent sentinel,
splices the stream into the local agent unix socket (separate agent_writers map,
TCP forwarding paths untouched). Rejects agent StreamOpens unless it opted in, so
a server cannot reach the agent without consent.
Server: when the client opted in and allow_agent_forwarding is set, binds a
per-session proxy unix socket (dir 0700, socket 0600) before the shell spawns,
exports its path as the session's SSH_AUTH_SOCK, and tunnels each connection back
to the client over the agent sentinel stream. Applies only to freshly spawned
shells (documented). Socket cleaned up on auth/forward failure and when the
accept loop ends. SECURITY rationale documented in comments.
Tests: 2 end-to-end integration tests (full chain identities round-trip via a
PTY-hosted client + looping fake agent; and "no -A => no proxy socket"). Docs
updated (README forwarding + disconnect-status note, spec §12.1). fmt + full test
suite green (122 tests).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Track A protocol hardening for native-v1.
1. Protocol VERSION discipline (protocol.rs, native.rs, dosh-server.rs,
dosh-client.rs): bump protocol::VERSION to 2 and NATIVE_PROTOCOL_VERSION to 2.
Foreign wire-version datagrams now get a clear named "protocol version
mismatch - upgrade dosh" reject from the server instead of a silent timeout
(peek_foreign_wire_version + VERSION_MISMATCH_REASON). The native handshake's
plaintext protocol_version is also checked server-side before any crypto via
check_native_protocol_version, returning a typed ProtocolVersionMismatch.
2. Transport rekey (spec section 11/9): server rotates a client's traffic key
after rekey_after_packets OR rekey_after_secs (config knobs). Rotated keys are
derived independently of the handshake keys from the current key plus fresh
server CSPRNG material shipped confidentially in an AEAD Rekey packet
(derive_rekey_session_key). The previous epoch's key is retained briefly so
in-flight pre-rekey packets still decrypt (matched by session_key_id), and
stale-epoch packets are ignored, not fatal. Client handles Rekey/RekeyAck.
3. Connection migration (spec section 11): every authenticated, replay-accepted
packet now migrates client.endpoint to the new source address (input, resize,
ping, ack, resume, stream*, rekey-ack), not just resume. Ping now verifies its
AEAD tag before acting so migration cannot be spoofed.
4. Native auth rate limiting: per-source-IP token bucket
(native_auth_rate_limit_per_minute) enforced in handle_native_client_hello
BEFORE any X25519/Ed25519 work; over-limit hellos get a non-crypto reject.
5. Speed: replaced O(sessions x clients) per-packet linear scans with an O(1)
HashMap<conn_id, session_name> index in ServerState, kept in sync on every
client insert/remove (attach handlers, detach, remove_client, cleanup reap,
session-exit drain).
New config keys (ServerConfig, with defaults): rekey_after_packets = 100000,
rekey_after_secs = 3600.
Tests: version-mismatch reject (no hang), rate-limit flood reject, rekey
round-trip end-to-end + key-derivation unit tests, source-address migration,
client-index sync + cleanup purge. fmt and full test suite green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Track B (milestone 5 / §16 hardening):
- tests/hostile_network.rs: in-process UDP relay/shim between a test
client and a real dosh-server that can drop, reorder, and duplicate
datagrams, and rebind its upstream socket mid-session. Asserts:
session survives loss/reorder, duplicated/replayed Input is applied at
most once, stale packets after resume are ignored (not fatal), and a
client source-address change preserves the session.
- tests/parser_robustness.rs: deterministic randomized tests throwing
garbage at every reachable public parser (packet decode, from_body for
all protocol/native structs, authorized_keys, known_hosts, host-key
line, ssh-ed25519 blob, bootstrap, attach ticket); asserts none panic.
- fuzz/: standalone cargo-fuzz crate (own [workspace], non-default
member) with libfuzzer-sys harnesses for packet decode, from_body,
authorized_keys, known_hosts, handshake structs+verifiers, and attach
tickets. README documents the run command.
- .github/workflows/ci.yml: add fuzz-smoke job (nightly + cargo-fuzz,
short -max_total_time per target, tolerant if tooling unavailable);
existing fmt/test/build/bench steps unchanged.
cargo fmt --check and cargo test are green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
DuProcess