CVE-2005-3857 in Linux
Summary
by MITRE
The time_out_leases function in locks.c for Linux kernel before 2.6.15-rc3 allows local users to cause a denial of service (kernel log message consumption) by causing a large number of broken leases, which is recorded to the log using the printk function.
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Analysis
by VulDB Data Team • 12/21/2024
The vulnerability identified as CVE-2005-3857 represents a significant denial of service weakness within the Linux kernel's locking subsystem that affects versions prior to 2.6.15-rc3. This flaw exists in the time_out_leases function located within the locks.c source file, which governs how the kernel handles file leasing mechanisms. File leasing is a mechanism that allows multiple processes to coordinate access to files, where one process can obtain a lease on a file and other processes must respect that lease. When a lease expires or becomes invalid, the system should properly clean up these lease entries without causing system instability or resource exhaustion.
The technical implementation of this vulnerability stems from how the kernel handles broken lease notifications during the lease timeout process. When multiple broken leases occur simultaneously, the system repeatedly invokes the printk function to log these events to the kernel log buffer. The printk function is responsible for writing messages to the kernel log, which is typically accessible via the /proc/kmsg interface or syslog facilities. This logging mechanism operates with a finite buffer size, and when numerous broken lease events occur in rapid succession, the logging system becomes overwhelmed with messages that consume all available buffer space. The continuous flood of log entries effectively consumes kernel resources and can lead to system instability or complete denial of service conditions.
This vulnerability operates under the principle of resource exhaustion, specifically targeting the kernel's logging subsystem which is essential for system monitoring and debugging operations. The flaw allows local users to exploit the system by creating numerous broken leases that trigger the logging mechanism, effectively consuming all available kernel log buffer space and preventing legitimate system messages from being recorded. The operational impact extends beyond simple resource exhaustion, as it can render the system effectively unusable for administrators who rely on kernel logs for monitoring and troubleshooting activities. This type of denial of service attack can be particularly damaging in production environments where system stability and availability are critical requirements.
The vulnerability demonstrates characteristics consistent with CWE-400, which addresses "Uncontrolled Resource Consumption," and aligns with ATT&CK technique T1499.001 for "Network Denial of Service" and T1565.001 for "Data Manipulation" when considering the broader impact on system operations. The flaw exists in the kernel's handling of lease timeouts where proper resource management and bounds checking are insufficient to prevent excessive logging. The issue represents a classic example of insufficient input validation and resource management in kernel space, where user-controlled conditions can lead to system-wide resource exhaustion. The exploitability is relatively straightforward as it requires only local access to create multiple broken leases, making it a particularly concerning vulnerability for systems where local users have access to the kernel's locking mechanisms.
Mitigation strategies for this vulnerability include upgrading to Linux kernel version 2.6.15-rc3 or later, where the problematic code has been modified to prevent excessive logging during lease timeout operations. Additionally, system administrators should implement proper monitoring of kernel log buffer usage and consider implementing log rotation policies to prevent buffer exhaustion. The kernel patch addresses the issue by modifying the logging behavior to limit the number of messages generated during lease timeout processing, ensuring that the system can continue normal operations even when multiple leases become broken. Organizations should also consider implementing access controls and privilege restrictions to limit local user access to file operations that might trigger this condition, reducing the attack surface for potential exploitation.