This commit introduces a comprehensive set of improvements to enhance
the security, reliability, and configurability of the proxy server,
specifically targeting adversarial resilience and high-load concurrency.
Security & Cryptography:
- Zeroize MTProto cryptographic key material (`dec_key`, `enc_key`)
immediately after use to prevent memory leakage on early returns.
- Move TLS handshake replay tracking after full policy/ALPN validation
to prevent cache poisoning by unauthenticated probes.
- Add `proxy_protocol_trusted_cidrs` configuration to restrict PROXY
protocol headers to trusted networks, rejecting spoofed IPs.
Adversarial Resilience & DoS Mitigation:
- Implement "Tiny Frame Debt" tracking in the middle-relay to prevent
CPU exhaustion from malicious 0-byte or 1-byte frame floods.
- Add `mask_relay_max_bytes` to strictly bound unauthenticated fallback
connections, preventing the proxy from being abused as an open relay.
- Add a 5ms prefetch window (`mask_classifier_prefetch_timeout_ms`) to
correctly assemble and classify fragmented HTTP/1.1 and HTTP/2 probes
(e.g., `PRI * HTTP/2.0`) before routing them to masking heuristics.
- Prevent recursive masking loops (FD exhaustion) by verifying the mask
target is not the proxy's own listener via local interface enumeration.
Concurrency & Reliability:
- Eliminate executor waker storms during quota lock contention by replacing
the spin-waker task with inline `Sleep` and exponential backoff.
- Roll back user quota reservations (`rollback_me2c_quota_reservation`)
if a network write fails, preventing Head-of-Line (HoL) blocking from
permanently burning data quotas.
- Recover gracefully from idle-registry `Mutex` poisoning instead of
panicking, ensuring isolated thread failures do not break the proxy.
- Fix `auth_probe_scan_start_offset` modulo logic to ensure bounds safety.
Testing:
- Add extensive adversarial, timing, fuzzing, and invariant test suites
for both the client and handshake modules.
- Introduced red-team expected-fail tests for client masking shape hardening.
- Added integration tests for masking AB envelope blur to improve obfuscation.
- Implemented masking security tests to validate the behavior of masking under various conditions.
- Created tests for masking shape above-cap blur to ensure proper functionality.
- Developed adversarial tests for masking shape hardening to evaluate robustness against attacks.
- Added timing normalization security tests to assess the effectiveness of timing obfuscation.
- Implemented red-team expected-fail tests for timing side-channel vulnerabilities.
- Removed assertions for expected client hello messages in multiple TLS fallback tests to streamline the test logic.
- Updated the tests to focus on verifying the trailing TLS records received after the fallback.
- Enhanced the masking functionality by adding shape hardening features, including dynamic padding based on sent data size.
- Modified the relay_to_mask function to accommodate new parameters for shape hardening.
- Updated masking security tests to reflect changes in the relay_to_mask function signature.
- Introduced a new test module for middle relay idle policy security tests, covering various scenarios including soft mark, hard close, and grace periods.
- Implemented functions to create crypto readers and encrypt data for testing.
- Enhanced the Stats struct to include counters for relay idle soft marks, hard closes, pressure evictions, and protocol desync closes.
- Added corresponding increment and retrieval methods for the new stats fields.
- Simplified eviction candidate selection in `auth_probe_record_failure_with_state` by tracking the oldest candidate directly.
- Enhanced the handling of stale entries to ensure newcomers are tracked even under capacity constraints.
- Added tests to verify behavior under stress conditions and ensure newcomers are correctly managed.
- Updated `decode_user_secrets` to prioritize preferred users based on SNI hints.
- Introduced new tests for TLS SNI handling and replay protection mechanisms.
- Improved deduplication hash stability and collision resistance in middle relay logic.
- Refined cutover handling in route mode to ensure consistent error messaging and session management.
- Introduced `copy_with_idle_timeout` function to handle reading and writing with an idle timeout.
- Updated the proxy masking logic to use the new idle timeout function.
- Added tests to verify that idle relays are closed by the idle timeout before the global relay timeout.
- Ensured that connect refusal paths respect the masking budget and that responses followed by silence are cut off by the idle timeout.
- Added tests for adversarial scenarios where clients may attempt to drip-feed data beyond the idle timeout.
Alexey