FastSync/CHANGELOG.md

Changelog

All notable changes to FastSync are documented here. Versions match PROTOCOL_VERSION (printed by fastsync --version); the client and server must run the same version because the handshake is strict.

[2.20.0] - 2026-09-13

Security

• Cap cumulative DirTimeList growth and bound pre-auth config-string memory (remote memory-exhaustion DoS).
• Daemon host access control (hosts allow/hosts deny, IPv4/IPv6/CIDR), configurable global max connections, connection audit logging, and a bounded auth failure delay throttle. IPv4-mapped peers are normalized and invalid patterns are rejected at parse time (no silent fail-open).
• Honor --timeout for protocol I/O and bound idle/session time to defeat keepalive slowloris; child-safe signal handling in the forked daemon.
• Compiler/linker hardening (_FORTIFY_SOURCE, stack protector, PIE, RELRO) and pinned build dependencies.

Fixed

• Use-after-free in the basis-dir oversize preflight.
• Placeholder Data leaks, missing_args leak, scanner chunk leak.
• Thread-safe logging; single fd owner and cleanup epilogue in the server handler.

Performance

• Metadata now crosses the wire as one packed frame (protocol 2.20.0).
• Delete keep-set and --files-from lookups indexed (O(n*m) → O(n)).
• Reused per-thread zstd contexts; TCP_NODELAY by default.
• Byte-bounded sender queues; removed a redundant scanner stat().

[2.19.0] - 2026-09-12

Security

• Daemon authentication rewritten as SCRAM-SHA-256 challenge/response (STATUS_AUTH_CHALLENGE → STATUS_AUTH_RESPONSE → STATUS_AUTH_OK/STATUS_AUTH_FAILED), replacing the old replayable static SHA-256(password) bearer credential. Each proof is bound to a fresh per-connection server nonce plus a client nonce, so a captured response can never be reused.
• Salted verifier store. --password-file/--early-input now hold user:$fastsync$1$pbkdf2-sha256$<iters>$<salt>$<stored_key>$<server_key> (PBKDF2-HMAC-SHA256, default 600000 iterations, range 100000–10000000). The legacy user:SHA256HEX form is hard-rejected; there is no auto-upgrade. Generate stores offline with fastsync-server --hash-credentials FILE [--iterations N].
• Username-enumeration hardening. Unknown/off-list users are answered with a dummy verifier whose salt is a deterministic per-username value (HMAC-SHA256(dummy_key, username)), using the store-wide uniform iteration count and a constant-time full-length membership scan. The dummy key is persisted in an owner-only <store>.dummykey sidecar (atomic publish, exact mode 0600) so challenges are stable across restarts.
• Verified transport for auth-required modules. A module with auth users accepts credentials only over verified TLS whose client certificate matches --client-cn, or — when --allow-unauthenticated is explicitly set — plaintext from a loopback peer. Remote plaintext is refused before any challenge. Clients must use --tls to send --password-file credentials to a non-loopback daemon; --client-cn is mandatory with --tls.
• Secret hygiene. The plaintext password, derived keys, nonces/proofs and the dummy key are wiped from memory on every path and never logged.
• Carried-over hardening: -K TOCTOU-safe directory walk (openat(O_NOFOLLOW) per component), always shell-quoted SSH remote path, TLS compression/renegotiation disabled, race-free (open-then-fstat) --password-file/--early-input checks, log-injection escaping, and lazy protocol debug escaping.

Added

• fastsync-server --hash-credentials FILE [--iterations N] offline tool.
• <store>.dummykey sidecar (auto-created, owner-only, 0600).
• Integration tests for auth replay rejection, malformed frames, legacy-store refusal, and the loopback/TLS transport policy; fuzz targets for config receive and daemon-auth parsing.

Changed

• Protocol version 2.18.0 → 2.19.0 (breaking). The config-frame auth block is now [present][username] (digest removed) and the auth challenge/response frames are interleaved between the config frame and its STATUS_OK. A 2.19.0 client and a 2.18.0 server (or vice versa) fail cleanly at the handshake.
• Daemon modules declaring auth users require a configured credential store at startup (fail closed); operators regenerate stores from plaintext with --hash-credentials.

Notes

• First tagged release. FastSync implements rsync-compatible file synchronization over TCP and SSH with TLS (OpenSSL), streaming zstd compression, multithreaded transfers, and incremental sync. See RSYNC_COMPAT.md for the flag-parity matrix.