CVE-2011-1082 in Linux
Summary
by MITRE
fs/eventpoll.c in the Linux kernel before 2.6.38 places epoll file descriptors within other epoll data structures without properly checking for (1) closed loops or (2) deep chains, which allows local users to cause a denial of service (deadlock or stack memory consumption) via a crafted application that makes epoll_create and epoll_ctl system calls.
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Analysis
by VulDB Data Team • 08/18/2024
The vulnerability described in CVE-2011-1082 resides within the Linux kernel's event polling mechanism, specifically in the fs/eventpoll.c file. This flaw represents a critical design oversight that affects how the kernel handles epoll file descriptors when they are nested within other epoll data structures. The vulnerability impacts Linux kernel versions prior to 2.6.38 and presents a significant risk to system stability and availability. From a cybersecurity perspective, this issue demonstrates the inherent dangers of insufficient input validation and recursive data structure management in kernel-level code, where improper boundary checking can lead to catastrophic system failures.
The technical flaw stems from the kernel's failure to implement proper loop detection and depth limitation mechanisms when processing epoll file descriptor nesting. When applications create epoll instances using epoll_create and subsequently manipulate these instances with epoll_ctl system calls, the kernel does not adequately verify whether the nesting creates closed loops or excessively deep chains. This lack of validation allows malicious or malformed applications to construct intricate epoll structures that either create circular references or exceed safe recursion depths. The vulnerability specifically targets the epoll subsystem's data structure traversal logic, which is responsible for managing file descriptor monitoring and event notification in high-performance I/O operations.
The operational impact of this vulnerability manifests as either deadlock conditions or excessive stack memory consumption, both of which constitute denial of service scenarios. When closed loops are created within epoll data structures, the kernel's event polling logic can enter infinite loops during traversal operations, leading to system hangs or complete deadlock states. Alternatively, when deep chains are established, the recursive processing consumes excessive stack memory, potentially causing stack overflow conditions that can crash the kernel or render the system unresponsive. These effects directly violate the fundamental availability principles of the information security triad and can be exploited by local users to disrupt system operations without requiring elevated privileges.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-674, which addresses the risk of uncontrolled recursion in software systems, and maps to ATT&CK technique T1499.001, which covers network denial of service attacks through resource exhaustion. The vulnerability also reflects broader concerns about kernel security boundaries and the importance of input validation at all levels of system operation. Organizations should implement immediate patch management protocols to upgrade to kernel versions 2.6.38 or later, where the fix addresses the recursive traversal logic and implements proper loop detection mechanisms. Additionally, system administrators should monitor for unusual epoll usage patterns and consider implementing resource limits on epoll operations as defensive measures against potential exploitation attempts.
The fix for this vulnerability involved implementing comprehensive validation checks within the epoll subsystem to detect and reject nested structures that would create closed loops or exceed predetermined depth limits. This solution demonstrates the importance of defensive programming practices in kernel development, where all recursive operations must include proper termination conditions and validation mechanisms. The vulnerability serves as a prime example of how seemingly minor design oversights in system-level code can have severe consequences for overall system stability and security posture.