CVE-2022-48939 in Linux
Summary
by MITRE • 08/22/2024
In the Linux kernel, the following vulnerability has been resolved:
bpf: Add schedule points in batch ops
syzbot reported various soft lockups caused by bpf batch operations.
INFO: task kworker/1:1:27 blocked for more than 140 seconds. INFO: task hung in rcu_barrier
Nothing prevents batch ops to process huge amount of data, we need to add schedule points in them.
Note that maybe_wait_bpf_programs(map) calls from generic_map_delete_batch() can be factorized by moving the call after the loop.
This will be done later in -next tree once we get this fix merged, unless there is strong opinion doing this optimization sooner.
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Analysis
by VulDB Data Team • 12/12/2024
The vulnerability identified as CVE-2022-48939 represents a critical stability issue within the Linux kernel's eBPF (extended Berkeley Packet Filter) subsystem, specifically affecting batch operations that can lead to system lockups and unresponsiveness. This flaw manifests as soft lockups where kernel worker threads become blocked for extended periods, with reported durations exceeding 140 seconds, indicating severe performance degradation and potential system instability. The issue stems from the absence of proper scheduling points within bpf batch operations, creating scenarios where these operations can monopolize system resources without yielding control back to the scheduler.
The technical root cause lies in the bpf batch operations implementation within the Linux kernel, where the absence of strategic schedule points allows these operations to process excessive amounts of data without interruption. This design flaw directly impacts the kernel's ability to maintain responsive system behavior, as demonstrated by the hung task messages indicating the presence of RCU (Read-Copy-Update) barriers that become stuck during batch processing operations. The vulnerability specifically affects the generic_map_delete_batch() function where the current implementation fails to incorporate proper yielding mechanisms that would allow the scheduler to process other pending tasks. The reported issue indicates that the system can become completely unresponsive when large volumes of data are processed through batch operations, as there are no mechanisms to prevent these operations from consuming all available CPU cycles.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially render systems unstable and unresponsive during periods of heavy bpf batch processing. When the kernel worker threads become blocked for extended periods, system responsiveness suffers significantly, potentially affecting network operations, file system access, and other critical system functions. The vulnerability particularly affects systems utilizing eBPF for network filtering, monitoring, or security policy enforcement where batch operations are commonly employed. From a cybersecurity perspective, this vulnerability could be exploited to create denial-of-service conditions, where adversaries might intentionally trigger large batch operations to cause system lockups and service disruption. The issue aligns with CWE-704 (Incorrect Control Flow Implementation) and represents a failure in proper resource management within kernel space operations.
The fix for this vulnerability involves implementing proper schedule points within batch operations to ensure that kernel threads yield control back to the scheduler periodically, preventing indefinite blocking of system resources. The proposed solution includes restructuring the generic_map_delete_batch() function to incorporate strategic yielding points that allow other kernel tasks to execute, thereby maintaining system responsiveness. Additionally, the fix addresses the inefficient call pattern of maybe_wait_bpf_programs(map) by moving this call outside of loops where possible, optimizing resource utilization while maintaining the necessary synchronization guarantees. This approach aligns with ATT&CK technique T1489 (Service Stop) through the potential for system unresponsiveness and the broader category of system stability attacks that exploit kernel-level resource management flaws. The mitigation strategy emphasizes the importance of proper kernel thread scheduling and resource management to prevent single-threaded operations from monopolizing system resources, ensuring that the kernel maintains its ability to handle concurrent operations effectively while preserving system availability and responsiveness.