attack-surface.md

Attack Surface Analysis for crossbeam-rs/crossbeam

Attack Surface: Data Races (Unsafe Code Interaction)

• Description: Incorrect interaction with crossbeam data structures from unsafe blocks within the application code, bypassing crossbeam's safety mechanisms.
  • How Crossbeam Contributes: crossbeam uses unsafe internally for performance. Application code that also uses unsafe and interacts incorrectly with crossbeam's internal data structures can introduce data races. This is a direct interaction with crossbeam's implementation.
  • Example: Directly manipulating the underlying memory of a crossbeam::queue::ArrayQueue from an unsafe block without adhering to the queue's internal synchronization mechanisms.
  • Impact: Memory corruption, undefined behavior, program crashes, potential security vulnerabilities (if the corrupted data is used in security-critical contexts).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Minimize unsafe: Avoid using unsafe code in the application if at all possible. This is the most effective mitigation.
    • Isolate unsafe: If unsafe is absolutely necessary, keep it highly localized, well-documented, and thoroughly reviewed.
    • Strictly Adhere to Invariants: If interacting with crossbeam internals from unsafe code, absolutely ensure that all internal invariants of the crossbeam data structures are maintained. This requires a deep understanding of crossbeam's implementation details.
    • Extensive Testing: Rigorous testing, including fuzzing, stress testing, and potentially formal verification, is essential for any unsafe code interacting with crossbeam.

Attack Surface: Deadlocks (Locking)

• Description: Two or more threads are blocked indefinitely, waiting for each other to release crossbeam synchronization primitives (locks).
  • How Crossbeam Contributes: crossbeam provides locking primitives like Mutex and ShardedLock. Incorrect usage of these primitives, such as acquiring locks in inconsistent orders across threads, directly leads to deadlocks.
  • Example: Thread 1 acquires a crossbeam::sync::Mutex for resource A, then tries to acquire another crossbeam::sync::Mutex for resource B. Thread 2 acquires the crossbeam::sync::Mutex for B, then tries to acquire the crossbeam::sync::Mutex for A.
  • Impact: Application hangs completely, resulting in a denial of service.
  • Risk Severity: High
  • Mitigation Strategies:
    • Lock Ordering: Establish a strict, consistent global order for acquiring all locks (including crossbeam locks) throughout the application. Always acquire locks in the same predetermined order.
    • Lock Hierarchy: Design a lock hierarchy to prevent circular dependencies between locks.
    • Deadlock Detection Tools: Utilize tools that can detect potential deadlocks during development and testing.
    • Timeouts: Consider using lock acquisition with timeouts (if supported by the specific crossbeam primitive) to prevent indefinite blocking.

Attack Surface: Deadlocks (Channels)

• Description: Senders and receivers on crossbeam::channel are blocked indefinitely, waiting for each other.
  • How Crossbeam Contributes: This is a direct consequence of misusing crossbeam::channel. Incorrect channel usage patterns, such as mismatched senders and receivers, or using synchronous channels without a corresponding receiver, lead directly to deadlocks.
  • Example: A sender attempts to send on a synchronous crossbeam::channel::bounded(0) channel, but there is no receiver currently ready to receive, causing the sender to block indefinitely.
  • Impact: Application hangs, leading to a denial of service.
  • Risk Severity: High
  • Mitigation Strategies:
    • Careful Channel Design: Thoroughly analyze channel usage patterns to ensure that senders and receivers are correctly paired and that the channel type (bounded, unbounded, synchronous) is appropriate for the use case.
    • Sufficient Capacity: Use bounded channels with sufficient capacity to avoid unnecessarily blocking senders.
    • Timeouts: Utilize send_timeout and recv_timeout methods (where available) to prevent indefinite blocking on channel operations.
    • Avoid Synchronous Channels When Possible: Synchronous channels (bounded(0)) are particularly prone to deadlocks; prefer asynchronous channels with a small buffer unless synchronous behavior is strictly required.

Attack Surface: Denial of Service (Resource Exhaustion - Unbounded Queues)

• Description: An attacker can cause the application to consume excessive memory by exploiting unbounded queues provided by crossbeam.
  • How Crossbeam Contributes: crossbeam provides unbounded queues (e.g., SegQueue). Using these without limits or backpressure mechanisms directly exposes the application to this vulnerability.
  • Example: A server uses a crossbeam::queue::SegQueue to queue incoming network requests. An attacker floods the server with requests, causing the queue to grow without bound until the server exhausts available memory and crashes.
  • Impact: Application crash, denial of service.
  • Risk Severity: High
  • Mitigation Strategies:
    • Bounded Queues: Use bounded queues (e.g., crossbeam::queue::ArrayQueue) whenever possible. This is the most direct and effective mitigation.
    • Backpressure: Implement mechanisms to slow down or reject new inputs when queues are approaching their capacity. This might involve sending error responses to clients or delaying processing.
    • Monitoring: Continuously monitor queue sizes and set alerts for excessive growth, allowing for proactive intervention.