CVE-2023-31084 in Linux
Summary
by MITRE • 04/24/2023
An issue was discovered in drivers/media/dvb-core/dvb_frontend.c in the Linux kernel 6.2. There is a blocking operation when a task is in !TASK_RUNNING. In dvb_frontend_get_event, wait_event_interruptible is called; the condition is dvb_frontend_test_event(fepriv,events). In dvb_frontend_test_event, down(&fepriv->sem) is called. However, wait_event_interruptible would put the process to sleep, and down(&fepriv->sem) may block the process.
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Analysis
by VulDB Data Team • 02/12/2025
The vulnerability described in CVE-2023-31084 represents a critical race condition and blocking operation issue within the Linux kernel's Digital Video Broadcasting subsystem, specifically in the dvb_frontend.c driver component. This flaw exists in kernel versions up to and including 6.2, making it a widespread concern for systems utilizing DVB hardware interfaces. The vulnerability stems from improper handling of synchronization primitives within the frontend event processing mechanism, creating a scenario where kernel threads can become indefinitely blocked due to conflicting state conditions.
The technical root cause involves a complex interplay between kernel synchronization mechanisms and task state management. When dvb_frontend_get_event is invoked, the system calls wait_event_interruptible with a condition that depends on dvb_frontend_test_event function. This test function attempts to acquire a semaphore using down(&fepriv->sem) while the calling task may already be in a non-running state. The fundamental issue occurs because wait_event_interruptible places the process in a sleeping state, but the semaphore acquisition operation can subsequently block the same process, creating a deadlock scenario where a task that should be responsive becomes permanently suspended.
This vulnerability directly relates to CWE-362, which addresses concurrent execution using lock and unlock operations, and CWE-121, concerning stack-based buffer overflow conditions. The flaw manifests as a potential system hang or deadlock condition that can severely impact multimedia and broadcasting applications relying on DVB hardware. The blocking operation occurs when a task transitions to a non-TASK_RUNNING state while simultaneously attempting to acquire a semaphore, violating fundamental kernel threading principles and creating a condition where the system becomes unresponsive to further frontend events.
The operational impact of this vulnerability extends beyond simple system hangs to potentially compromise the entire multimedia subsystem of affected devices. Systems utilizing DVB receivers, satellite tuners, or digital television hardware could experience complete service disruption, with applications unable to process incoming broadcast events or respond to user interactions. This affects a wide range of devices including set-top boxes, digital television receivers, and embedded systems with DVB capabilities. The vulnerability is particularly concerning in embedded environments where system stability and real-time processing requirements are critical for proper operation.
Mitigation strategies for CVE-2023-31084 require immediate kernel updates to versions containing the patched dvb_frontend.c implementation. System administrators should prioritize patching affected systems, especially those running kernel versions 6.2 or earlier, as the vulnerability can be exploited by malicious actors to create persistent system hangs or denial-of-service conditions. Additionally, monitoring for abnormal task states and implementing proper timeout mechanisms for frontend operations can provide temporary workarounds while awaiting official patches. Organizations should also consider implementing redundant monitoring systems to detect when DVB subsystems become unresponsive, as the vulnerability can silently cause system degradation without obvious error indicators. The fix typically involves restructuring the semaphore acquisition logic to prevent blocking operations during task state transitions, ensuring proper synchronization between event processing and resource access operations.