mitigations.md

Mitigation Strategies Analysis for tokio-rs/tokio

Mitigation Strategy: Task Budgeting/Limiting (using tokio::sync::Semaphore)

Mitigation Strategy: Task Budgeting/Limiting using tokio::sync::Semaphore.

• Description:

  1. Identify Critical Resources: Determine which resources (e.g., concurrent database connections, external API calls, CPU-intensive tasks managed by Tokio) need to be limited.
  2. Create a Semaphore: Instantiate a tokio::sync::Semaphore with a specific number of permits, representing the maximum allowed concurrent access to the resource. Example: let db_semaphore = Arc::new(Semaphore::new(10)); (allows 10 concurrent database connections).
  3. Acquire Permits Before Resource Access: Before any code that accesses the limited resource within a Tokio task, asynchronously acquire a permit from the semaphore using db_semaphore.clone().acquire().await?;. This will block (asynchronously, within the Tokio runtime) if all permits are currently in use.
  4. Release Permits After Resource Access: Crucially, ensure that the permit is released after the resource is no longer needed, even if an error occurs. Use a defer or finally block (if available) or a Drop implementation (as shown in the previous response) to guarantee release.
  5. Handle Permit Acquisition Errors: The acquire().await? call can return an error. Handle this error appropriately.
  6. Consider try_acquire(): For non-critical operations, use try_acquire() to attempt to acquire a permit without blocking within the Tokio runtime.

• Threats Mitigated:

  • Resource Exhaustion (DoS): (Severity: High) - Prevents an attacker from overwhelming the system by spawning excessive Tokio tasks that consume a specific resource.
  • Uncontrolled Task Spawning: (Severity: Medium) - Limits the overall number of concurrent Tokio tasks.

• Impact:

  • Resource Exhaustion (DoS): Risk significantly reduced.
  • Uncontrolled Task Spawning: Risk reduced.

• Currently Implemented:

  • Example: Database connection pooling (in src/db/mod.rs).
  • Example: External API rate limiting (in src/external_api.rs).

• Missing Implementation:

  • CPU-intensive task limiting (missing in src/image_processing.rs).
  • Global task limit (missing).

Mitigation Strategy: Timeout Handling (using tokio::time::timeout)

Mitigation Strategy: Universal Timeout Application with tokio::time::timeout.

• Description:

  1. Identify Asynchronous Operations: Identify all asynchronous operations managed by Tokio, including network I/O, database queries, external API calls, and custom futures.
  2. Wrap with tokio::time::timeout: Wrap each asynchronous operation with tokio::time::timeout. See the previous response for a detailed code example.
  3. Choose Appropriate Timeout Values: Carefully select timeout durations.
  4. Handle Timeout Errors: Handle both timeout errors (Err(Elapsed)) and inner operation errors (Ok(Err(e))) appropriately.
  5. Apply to All Futures: This is critical. Apply timeouts universally to all Tokio-managed futures.

• Threats Mitigated:

  • Resource Exhaustion (DoS): (Severity: High) - Prevents slow or stalled Tokio-managed operations from indefinitely consuming resources.
  • Hanging Operations: (Severity: Medium)

• Impact:

  • Resource Exhaustion (DoS): Risk dramatically reduced.
  • Hanging Operations: Risk significantly reduced.

• Currently Implemented:

  • Network I/O timeouts (in src/network/client.rs and src/network/server.rs).
  • Database query timeouts (in src/db/mod.rs).

• Missing Implementation:

  • External API call timeouts (partially missing in src/external_api.rs).
  • Long-running computations spawned with spawn_blocking (missing in src/long_running_task.rs).

Mitigation Strategy: Backpressure Handling (using tokio::sync::mpsc)

Mitigation Strategy: Backpressure with Bounded Channels (tokio::sync::mpsc).

• Description:

  1. Identify Data Streams: Identify parts of the application that process streams of data within the Tokio runtime.
  2. Use Bounded Channels: Use tokio::sync::mpsc::channel(capacity) to create bounded channels for communication between different Tokio tasks.
  3. Sender-Side Handling: When sending data to the channel, use send().await. If the channel is full, this will block (asynchronously, within the Tokio runtime) until space becomes available.
  4. Receiver-Side Handling: The receiver processes messages from the channel.
  5. Monitor Channel Capacity: Optionally, monitor the channel's capacity.
  6. Consider try_send(): In some cases, use try_send() to attempt to send a message without blocking within the Tokio runtime.

• Threats Mitigated:

  • Resource Exhaustion (DoS): (Severity: Medium)
  • Memory Leaks: (Severity: Medium)

• Impact:

  • Resource Exhaustion (DoS): Risk reduced.
  • Memory Leaks: Risk reduced.

• Currently Implemented:

  • Message queue processing (in src/message_queue.rs).

• Missing Implementation:

  • Incoming network request handling (missing in src/network/server.rs).

Mitigation Strategy: Safe Shared State Management (using tokio::sync)

Mitigation Strategy: Using tokio::sync::Mutex (and other tokio::sync primitives) for Shared Mutable State.

• Description:

  1. Identify Shared Mutable State: Identify data accessed and modified by multiple Tokio tasks.
  2. Wrap with Arc<tokio::sync::Mutex<T>>: Wrap the shared data.
  3. Acquire Lock Asynchronously: Before accessing, use mutex.lock().await.
  4. Release Lock After Access: The lock guard automatically releases the lock when it goes out of scope.
  5. Minimize Lock Contention: Keep the critical section short.
  6. Avoid Holding Locks Across await Points (Generally): Avoid this pattern to prevent deadlocks within the Tokio runtime.
  7. Use other tokio::sync primitives when appropriate: Use tokio::sync::RwLock, tokio::sync::watch, tokio::sync::broadcast, tokio::sync::oneshot as needed.

• Threats Mitigated:

  • Data Races: (Severity: High)
  • Race Conditions: (Severity: High)

• Impact:

  • Data Races: Risk eliminated.
  • Race Conditions: Risk significantly reduced.

• Currently Implemented:

  • Shared application configuration (in src/config.rs).
  • Shared counter for tracking active connections (in src/network/server.rs).

• Missing Implementation:

  • Shared cache (partially missing in src/cache.rs).

Mitigation Strategy: Panic Handling in Tasks (using tokio::task::JoinHandle)

Mitigation Strategy: Using tokio::task::JoinHandle for Panic Propagation.

• Description:

  1. Spawn Tasks with tokio::task::spawn: Use tokio::task::spawn to create new asynchronous tasks.
  2. Retain the JoinHandle: Store the JoinHandle.
  3. await the JoinHandle: await the JoinHandle to wait for the task to complete.
  4. Handle the Result: Handle the Ok(_) and Err(JoinError) cases, checking for panics using JoinError::is_panic().
  5. Log and/or Recover: Log panics and potentially attempt recovery.

• Threats Mitigated:

  • Unhandled Panics: (Severity: Medium)
  • Resource Leaks: (Severity: Medium)

• Impact:

  • Unhandled Panics: Risk significantly reduced.
  • Resource Leaks: Risk reduced.

• Currently Implemented:

  • All major task spawning points.

• Missing Implementation:

  • No missing implementation.

Mitigation Strategy: Controlled spawn_blocking Usage (with tokio::task::spawn_blocking and potentially tokio::sync::Semaphore)

Mitigation Strategy: Limiting and Monitoring spawn_blocking.

• Description:

  1. Identify Blocking Operations: Identify truly blocking operations.
  2. Use tokio::task::spawn_blocking: Use spawn_blocking to offload these to a separate thread pool.
  3. Configure Thread Pool Size: Configure the Tokio runtime's blocking thread pool size appropriately.
  4. Consider a Semaphore: Use a tokio::sync::Semaphore to limit concurrently running spawn_blocking tasks.
  5. Short-Lived Tasks: Design blocking tasks to be short-lived.
  6. Timeouts (using tokio::time::timeout): Apply timeouts to the futures returned by spawn_blocking.

• Threats Mitigated:

  • Tokio Runtime Starvation: (Severity: Medium)
  • Resource Exhaustion (Threads): (Severity: Medium)

• Impact:

  • Tokio Runtime Starvation: Risk significantly reduced.
  • Resource Exhaustion (Threads): Risk reduced.

• Currently Implemented:

  • File I/O operations (in src/file_io.rs).
  • CPU-bound cryptographic operations (in src/crypto.rs).

• Missing Implementation:

  • Long-running computations (partially missing in src/long_running_task.rs).