threat-modeling.md

Threat Model Analysis for crossbeam-rs/crossbeam

Threat: Unbounded Channel Overflow

• Description: An attacker could flood a producer thread with requests, causing it to send messages to an unbounded crossbeam::channel faster than the consumer can process them. The attacker doesn't need direct access to the channel; they just need to trigger the producer's behavior.
  • Impact: Leads to Out-of-Memory (OOM) condition, crashing the application and causing a Denial of Service (DoS).
  • Affected Component: crossbeam::channel (specifically unbounded channels: crossbeam::channel::unbounded()).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Use bounded channels (crossbeam::channel::bounded()) with a carefully chosen capacity.
    • Implement backpressure: The producer should monitor the channel's fill level and slow down or pause if it's approaching the limit. This might involve feedback from the consumer.
    • Rate-limit the producer's input or processing.
    • Implement monitoring and alerting to detect excessive channel growth.

Threat: Deadlock in Channel Communication

• Description: A poorly designed application using crossbeam::channel could be vulnerable to deadlock. A deadlock occurs when two or more threads are blocked indefinitely, waiting for each other to release resources (in this case, to send or receive on a channel). This can happen with complex channel interactions.
  • Impact: Complete application hang, requiring a restart. This is a Denial of Service (DoS).
  • Affected Component: crossbeam::channel (all channel types), potentially in combination with other synchronization primitives.
  • Risk Severity: High
  • Mitigation Strategies:
    • Carefully analyze channel communication patterns to avoid circular dependencies.
    • Use a deadlock detection tool during development (e.g., parking_lot's deadlock detection, though external to crossbeam).
    • Establish clear ownership and communication protocols between threads.
    • Minimize the complexity of channel interactions.
    • Consider using timeouts on send/receive operations to prevent indefinite blocking.

Threat: Deadlock with Parker and Unparker

• Description: Incorrect usage of crossbeam::sync::Parker and crossbeam::sync::Unparker can lead to deadlocks. For example, a thread might park() itself without a corresponding unpark() call from another thread, or the unpark() might happen before the park(), leading to a missed wakeup.
  • Impact: Application hang (DoS), potentially affecting only a subset of threads.
  • Affected Component: crossbeam::sync::Parker, crossbeam::sync::Unparker.
  • Risk Severity: High
  • Mitigation Strategies:
    • Ensure a one-to-one correspondence between park() and unpark() calls.
    • Carefully consider the order of operations and potential race conditions.
    • Use higher-level synchronization primitives (e.g., channels) if possible, as they are often easier to reason about.
    • Thoroughly test and review code that uses Parker and Unparker.

Threat: Data Race with Atomic Operations

• Description: Incorrect use of crossbeam::atomic can introduce a data race. If multiple threads access and modify a shared atomic variable without using the correct memory ordering, the result can be unpredictable, leading to data corruption or inconsistent state.
  • Impact: Data corruption, unpredictable application behavior, potential information disclosure (through corrupted data), potential for exploitation depending on the nature of the corrupted data.
  • Affected Component: crossbeam::atomic (all atomic types and operations).
  • Risk Severity: High
  • Mitigation Strategies:
    • Use the appropriate memory ordering (SeqCst, Acquire, Release, Relaxed, AcqRel) for each atomic operation. Understand the implications of each ordering.
    • Prefer higher-level abstractions (e.g., data structures built on top of atomics) when possible.
    • Use tools like ThreadSanitizer (part of LLVM) to detect data races during testing.

Threat: Use-After-Free with Epoch-Based Reclamation

• Description: Incorrect use of crossbeam::epoch can lead to use-after-free vulnerabilities. If a thread accesses a memory location that has been reclaimed by another thread (because it was no longer protected by a Guard), it can read invalid data or cause a crash.
  • Impact: Application crash (DoS), potential for arbitrary code execution (depending on the specifics of the use-after-free), data corruption.
  • Affected Component: crossbeam::epoch (and data structures that use it, such as lock-free queues).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Strictly adhere to the rules of epoch-based reclamation. Ensure proper synchronization between threads.
    • Use Guard objects correctly to protect access to shared data. Ensure Guards are dropped only when the data is no longer needed.
    • Thoroughly test and review code that uses crossbeam::epoch.
    • Consider using a memory safety checker (e.g., Miri, part of the Rust project) to detect use-after-free errors.

Threat: Panic-Induced Inconsistent State

• Description: A thread panics while interacting with a crossbeam component (e.g., while holding a lock implemented using crossbeam primitives, during a channel operation, or within an epoch-protected region). If not handled, this can leave shared data structures in an inconsistent state.
  • Impact: Data corruption, deadlock, or other unpredictable behavior in other threads that access the same shared resources. Potentially a DoS if other threads become blocked.
  • Affected Component: Potentially any crossbeam component, as panics can occur in any code interacting with shared resources managed by or used in conjunction with crossbeam.
  • Risk Severity: High
  • Mitigation Strategies:
    • Use std::panic::catch_unwind to catch panics within threads and attempt to recover gracefully.
    • Ensure that shared resources are properly cleaned up or reset in case of a panic (e.g., using RAII).
    • Log panics for debugging.
    • Minimize the amount of code that executes while holding shared resources.