resource_load_scheduler.md

Resource Load Scheduler Security

Component Focus: Chromium's resource load scheduler in Blink, specifically the ResourceLoadScheduler class in third_party/blink/renderer/platform/loader/fetch/resource_load_scheduler.cc. This component prioritizes and schedules resource loading.

Potential Logic Flaws:

• Resource Starvation: Vulnerabilities could cause critical resources to be delayed or blocked, potentially disrupting page rendering. A malicious website could exploit the scheduler to prioritize its own resources, as the scheduling logic relies on request priorities and throttling policies, which could be manipulated. The Request and SetPriority functions, which handle incoming resource requests and priority changes, are critical for analysis.
• Race Conditions: The asynchronous nature of resource loading and the scheduler's interaction with other components, such as the network stack and the frame/worker scheduler, could introduce race conditions. The Request, Release, and OnLifecycleStateChanged functions, which handle asynchronous requests, resource releases, and lifecycle state changes, respectively, are potential sources of race conditions if not properly synchronized.
• Denial of Service (DoS): The scheduler could be targeted by DoS attacks, such as flooding with requests or manipulating priorities to exhaust resources. The Request function, which handles incoming requests, and the IsRunningThrottleableRequestsLessThanOutStandingLimit function, which checks resource limits, are crucial for DoS mitigation. The lack of robust input validation and rate limiting in these functions could be exploited.
• Inefficient Scheduling: Inefficient scheduling algorithms could negatively impact performance, indirectly affecting security by making the browser more susceptible to other attacks. The GetNextPendingRequest and MaybeRun functions, which handle the scheduling logic, should be reviewed for performance and efficiency.

Further Analysis and Potential Issues:

The resource_load_scheduler.cc file ($7,866 VRP payout) implements the ResourceLoadScheduler class. Key areas and functions to investigate include:

• Request Handling and Prioritization (Request, SetPriority, IsClientDelayable): These functions handle incoming resource requests, manage their priorities, and determine whether requests can be delayed. They should be reviewed for potential resource starvation vulnerabilities, race conditions, and DoS mitigation. The handling of different throttle options (ThrottleOption) and resource load priorities (ResourceLoadPriority) is crucial for security and performance. The interaction with the ResourceFetcherProperties is also important for understanding how resource requests are classified and prioritized.

• Resource Release and Scheduling (Release, GetNextPendingRequest, MaybeRun): These functions manage the release of completed resource requests and schedule pending requests. They should be reviewed for proper resource cleanup, race conditions, and efficient scheduling algorithms. The handling of different release options (ReleaseOption) and the interaction with the pending request queues are important for security and performance.

• Throttling and Limits (LoosenThrottlingPolicy, IsRunningThrottleableRequestsLessThanOutStandingLimit, GetOutstandingLimit, SetOutstandingLimitForTesting): These functions manage the throttling policy and resource limits. They should be reviewed for potential DoS vulnerabilities and their effectiveness in preventing resource exhaustion. The handling of different throttling policies (ThrottlingPolicy) and the interaction with the frame/worker scheduler are crucial for security.

• Interaction with Frame/Worker Scheduler (OnLifecycleStateChanged, Shutdown): These functions handle changes in the lifecycle state of the frame/worker scheduler. They should be reviewed for proper handling of state transitions, resource cleanup, and potential race conditions. The interaction with the FrameOrWorkerScheduler and the handling of throttled states are important for security and performance.

• Console Logging and Diagnostics (ShowConsoleMessageIfNeeded): This function displays console messages about throttled requests. While not directly related to security, it can provide valuable diagnostic information for identifying potential issues or misconfigurations.

• Other Considerations:

  • Input Validation: The Request and SetPriority functions should be reviewed for robust input validation to prevent manipulation of request parameters or priorities by malicious actors.
  • Error Handling: The ResourceLoadScheduler should handle errors during resource loading and scheduling gracefully and securely, preventing information leakage or unexpected behavior.
  • Timing and Synchronization: The timing and synchronization of resource requests and their interaction with the network stack and other components should be carefully analyzed for potential race conditions or vulnerabilities.

Areas Requiring Further Investigation:

• Analyze request handling and prioritization for resource starvation, race conditions, and DoS.
• Review resource release and scheduling for proper cleanup, race conditions, and efficiency.
• Analyze throttling and limits for DoS vulnerabilities and resource exhaustion prevention.
• Investigate the interaction with the frame/worker scheduler for proper state handling and race conditions.
• Review input validation in Request and SetPriority.
• Analyze error handling during resource loading and scheduling.
• Investigate timing and synchronization of resource requests for potential race conditions.
• Test the scheduler with various resource load scenarios and edge cases.

Secure Contexts and Resource Load Scheduler:

The resource load scheduler should operate securely regardless of context.

Privacy Implications:

The scheduler's behavior could reveal information about browsing activity or resource usage. The implementation should minimize leakage of potentially sensitive information.

Additional Notes:

Files reviewed: third_party/blink/renderer/platform/loader/fetch/resource_load_scheduler.cc.