CVE-2016-2547 in Linux
Summary
by MITRE
sound/core/timer.c in the Linux kernel before 4.4.1 employs a locking approach that does not consider slave timer instances, which allows local users to cause a denial of service (race condition, use-after-free, 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-2016-2547 resides within the Linux kernel's sound subsystem, specifically in the sound/core/timer.c file. This issue affects kernel versions prior to 4.4.1 and represents a critical race condition flaw that can be exploited by local attackers to compromise system stability. The vulnerability stems from an inadequate locking mechanism that fails to account for slave timer instances within the audio subsystem's timer management architecture. This oversight creates a scenario where concurrent access to timer resources can lead to unpredictable behavior and system instability.
The technical flaw manifests when a local user executes a crafted ioctl call that manipulates timer instances within the sound subsystem. The kernel's locking implementation does not properly synchronize access to timer resources when slave timer instances are involved, creating a window where multiple threads or processes can simultaneously access the same timer object. This race condition can result in a use-after-free error when the kernel attempts to access memory that has already been released, leading to kernel memory corruption. The improper locking approach means that the system cannot guarantee atomic access to timer resources, allowing for concurrent modifications that can corrupt internal data structures.
The operational impact of this vulnerability is severe and can result in complete system compromise through denial of service conditions. When exploited, the vulnerability can cause system crashes, kernel oops messages, and potentially allow for privilege escalation or arbitrary code execution in certain scenarios. Local attackers with minimal privileges can leverage this flaw to destabilize the entire system, making it particularly dangerous in multi-user environments where untrusted users might have access to audio subsystem interfaces. The vulnerability affects systems running Linux kernel versions up to and including 4.4.0, impacting a wide range of devices including servers, desktops, and embedded systems that utilize the Linux audio subsystem.
This vulnerability maps to CWE-362, which describes a race condition in the context of concurrent access to shared resources without proper synchronization. The issue also aligns with ATT&CK technique T1068, which covers 'Local Privilege Escalation' through the exploitation of kernel vulnerabilities. The lack of proper locking in the timer subsystem creates a pathway for attackers to manipulate kernel memory structures, potentially leading to system compromise. The use-after-free aspect of this vulnerability can be particularly dangerous as it can allow for memory corruption that might be exploitable for privilege escalation. Mitigation strategies include updating to kernel version 4.4.1 or later, where the locking mechanism has been corrected to properly handle slave timer instances. System administrators should also consider implementing additional security measures such as restricting access to audio subsystem interfaces and monitoring for unusual ioctl activity. The fix implemented in the patched kernel version ensures proper synchronization of timer operations across all instances, including slave timers, eliminating the race condition that allowed for the exploitation of this vulnerability.