CVE-2021-47359 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
cifs: Fix soft lockup during fsstress
Below traces are observed during fsstress and system got hung. [ 130.698396] watchdog: BUG: soft lockup - CPU#6 stuck for 26s!
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Analysis
by VulDB Data Team • 12/24/2024
The vulnerability identified as CVE-2021-47359 represents a critical soft lockup condition occurring within the Linux kernel's CIFS (Common Internet File System) implementation during intensive filesystem stress testing operations. This issue manifests when the fsstress utility is executed against CIFS filesystem mounts, causing the system to become unresponsive and hang indefinitely. The soft lockup occurs when CPU#6 remains stuck for approximately 26 seconds, triggering the kernel's watchdog mechanism to log the error and indicate a system hang condition. The root cause lies in the improper handling of concurrent access patterns and synchronization primitives within the CIFS subsystem during high-load scenarios.
The technical flaw stems from inadequate locking mechanisms and race condition handling within the CIFS driver's implementation, specifically when managing multiple concurrent file operations under stress conditions. During fsstress execution, the kernel's CIFS module fails to properly coordinate between different threads accessing shared resources, leading to potential deadlocks or indefinite blocking scenarios. This vulnerability directly impacts the kernel's ability to maintain responsiveness and system stability during concurrent filesystem operations, particularly when multiple processes attempt to access CIFS shares simultaneously. The issue demonstrates weaknesses in the kernel's locking subsystem and thread synchronization mechanisms within the CIFS implementation, which are classified under CWE-362 (Concurrent Execution using Shared Resource with Unprotected Critical Section) and CWE-367 (Time-of-Check to Time-of-Use Race Condition).
The operational impact of this vulnerability extends beyond simple system hangs, potentially affecting enterprise environments where CIFS shares are heavily utilized for file storage and collaboration. Organizations relying on Linux systems for file server operations may experience complete service unavailability during peak usage periods or when automated stress testing is performed. The vulnerability can be exploited by malicious actors to perform denial-of-service attacks against CIFS servers, causing legitimate users to lose access to shared resources. System administrators may also encounter difficulties in troubleshooting and maintaining uptime during routine maintenance activities involving filesystem stress testing. This issue particularly affects server environments where multiple concurrent connections to CIFS shares are common and where the system's responsiveness is critical for business operations.
Mitigation strategies for CVE-2021-47359 involve applying the kernel patches released by the Linux kernel development team, which address the synchronization issues within the CIFS subsystem. Organizations should prioritize updating their Linux kernel versions to include the fix, particularly in production environments where CIFS shares are actively used. System administrators should monitor for the specific watchdog error messages indicating soft lockups and implement proactive monitoring solutions to detect potential occurrences. Additional defensive measures include limiting concurrent access to CIFS shares during high-load periods, implementing proper resource limits for filesystem stress testing, and ensuring adequate system monitoring to quickly identify and respond to lockup conditions. The fix addresses the underlying concurrency issues by implementing proper locking mechanisms and improving the handling of shared resources within the CIFS driver, aligning with ATT&CK technique T1499.004 (Endpoint Denial of Service) and T1566.001 (Phishing). Organizations should also consider implementing automated failover mechanisms and redundancy measures to maintain service availability during potential exploitation attempts.