CVE-2016-2545 in Linux
Summary
by MITRE
The snd_timer_interrupt function in sound/core/timer.c in the Linux kernel before 4.4.1 does not properly maintain a certain linked list, which allows local users to cause a denial of service (race condition and system crash) via a crafted ioctl call.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-2545 resides within the Linux kernel's sound subsystem, specifically in the snd_timer_interrupt function located in sound/core/timer.c. This flaw represents a critical race condition that can be exploited by local attackers to trigger system crashes and denial of service conditions. The vulnerability affects Linux kernel versions prior to 4.4.1, making it a significant concern for systems running older kernel versions where patching may not have been implemented.
The technical root cause of this vulnerability stems from improper maintenance of a linked list data structure within the timer interrupt handling mechanism. When a crafted ioctl call is made to the sound subsystem, the snd_timer_interrupt function fails to properly synchronize access to the linked list structure, creating a race condition scenario. This race condition occurs during the manipulation of the linked list nodes that track timer events, allowing for potential memory corruption or invalid pointer dereferences. The improper list management can lead to situations where list nodes are freed while still being referenced or where new nodes are added to invalid memory locations.
The operational impact of this vulnerability is severe as it allows local users to cause system instability through deliberate exploitation. An attacker with local access can craft specific ioctl commands that trigger the race condition, potentially leading to kernel oops, system crashes, or complete system hangs. This denial of service condition can be particularly damaging in production environments where system availability is critical. The vulnerability does not require special privileges beyond local access, making it accessible to any user who can execute programs on the affected system. The exploitation typically results in a kernel panic or system reboot, effectively denying service to legitimate users and potentially causing data loss.
This vulnerability maps to CWE-367, which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and can be categorized under ATT&CK technique T1499.1 for Network Denial of Service. The attack surface is primarily through the Linux sound subsystem's timer functionality, which is accessed via standard ioctl system calls. The vulnerability demonstrates poor resource management practices in kernel code and highlights the importance of proper synchronization mechanisms when handling shared data structures. Security practitioners should prioritize patching affected systems to kernel version 4.4.1 or later, where the linked list management has been corrected to prevent the race condition. Additionally, system administrators should monitor for any signs of exploitation attempts and ensure proper access controls to limit local user privileges where possible. The fix implemented in kernel 4.4.1 involved proper locking mechanisms around the linked list operations to prevent concurrent access that could lead to the race condition described in CVE-2016-2545.