CVE-2021-47252 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
batman-adv: Avoid WARN_ON timing related checks
The soft/batadv interface for a queued OGM can be changed during the time the OGM was queued for transmission and when the OGM is actually transmitted by the worker.
But WARN_ON must be used to denote kernel bugs and not to print simple warnings. A warning can simply be printed using pr_warn.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/21/2024
The vulnerability identified as CVE-2021-47252 resides within the Linux kernel's batman-adv module, which provides advanced routing capabilities for wireless mesh networks. This issue specifically affects the handling of Originator Message Groups (OGMs) that are queued for transmission within the mesh network infrastructure. The problem manifests when the soft/batadv interface associated with a queued OGM undergoes changes between the moment the OGM is placed in the transmission queue and when it is actually transmitted by the worker thread responsible for network packet forwarding.
The technical flaw stems from the inappropriate use of kernel debugging macros within the batman-adv subsystem. Specifically, the code employs WARN_ON macros for timing-related checks that are not actually indicative of kernel bugs or internal inconsistencies. According to kernel development best practices and the Linux kernel coding guidelines, WARN_ON macros should only be used to detect genuine kernel bugs or internal state corruption that should never occur under normal operating conditions. The misuse of this macro creates a situation where legitimate interface changes during the queuing period trigger false positive warnings that do not represent actual kernel failures but rather normal operational behavior.
This vulnerability represents a deviation from the established CWE classification for improper use of debugging macros, specifically CWE-754, which deals with "Improper Check for Unusual or Exceptional Conditions." The operational impact of this issue is significant as it can lead to excessive logging and false positive alerts that may obscure real kernel issues. When the system encounters normal interface transitions during OGM transmission timing, the inappropriate use of WARN_ON causes unnecessary kernel warnings to be generated, potentially overwhelming system logs and making it difficult for administrators to identify actual kernel bugs or security issues.
The improper use of kernel debugging facilities also violates established security practices by potentially exposing system internals through excessive logging. From an operational security perspective, this vulnerability could be exploited by adversaries to create denial-of-service conditions through log flooding or to mask actual security issues by generating false positive warnings. The ATT&CK framework would categorize this under T1490 - "Inhibit System Recovery" through log manipulation, as the excessive warnings could interfere with system monitoring and incident response processes.
Mitigation strategies for CVE-2021-47252 involve updating to kernel versions that contain the patched batman-adv module implementation where WARN_ON has been replaced with appropriate pr_warn logging for timing-related checks. System administrators should ensure their mesh network infrastructure operates on kernel versions that have addressed this specific issue, as the patch ensures that legitimate interface transitions during OGM transmission no longer trigger false kernel warnings. Organizations maintaining wireless mesh networks should conduct regular kernel updates and vulnerability assessments to prevent similar issues from arising in their network infrastructure. The fix aligns with kernel security best practices and maintains the distinction between actual kernel bugs and normal operational conditions, ensuring that system logs accurately reflect genuine security or stability concerns rather than routine interface management operations.