CVE-2024-58057

In the Linux kernel, the following vulnerability has been resolved:

idpf: convert workqueues to unbound

When a workqueue is created with WQ_UNBOUND, its work items are served by special worker-pools, whose host workers are not bound to any specific CPU. In the default configuration (i.e. when queue_delayed_work and friends do not specify which CPU to run the work item on), WQ_UNBOUND allows the work item to be executed on any CPU in the same node of the CPU it was enqueued on. While this solution potentially sacrifices locality, it avoids contention with other processes that might dominate the CPU time of the processor the work item was scheduled on.

This is not just a theoretical problem: in a particular scenario misconfigured process was hogging most of the time from CPU0, leaving less than 0.5% of its CPU time to the kworker. The IDPF workqueues that were using the kworker on CPU0 suffered large completion delays as a result, causing performance degradation, timeouts and eventual system crash.

• I have also run a manual test to gauge the performance improvement. The test consists of an antagonist process (./stress --cpu 2) consuming as much of CPU 0 as possible. This process is run under taskset 01 to bind it to CPU0, and its priority is changed with chrt -pQ 9900 10000 ${pid} and renice -n -20 ${pid} after start.

  Then, the IDPF driver is forced to prefer CPU0 by editing all calls to queue_delayed_work, mod_delayed_work, etc... to use CPU 0.

  Finally, ktraces for the workqueue events are collected.

  Without the current patch, the antagonist process can force arbitrary delays between workqueue_queue_work and workqueue_execute_start, that in my tests were as high as 30ms. With the current patch applied, the workqueue can be migrated to another unloaded CPU in the same node, and, keeping everything else equal, the maximum delay I could see was 6us.

This vulnerability is rated as Moderate severity because exploitation requires local access, hardware utilizing the Intel IDPF network driver, and substantial CPU starvation to cause a denial of service. The flaw is confined to kernel thread starvation leading to potential system crashes, without permitting privilege escalation or compromising system confidentiality and integrity. Standard Red Hat Enterprise Linux systems without Intel IDPF network devices or where the module is not loaded are unaffected.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.