CVE-2011-3638 in Linux
Summary
by MITRE
fs/ext4/extents.c in the Linux kernel before 3.0 does not mark a modified extent as dirty in certain cases of extent splitting, which allows local users to cause a denial of service (system crash) via vectors involving ext4 umount and mount operations.
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Analysis
by VulDB Data Team • 03/19/2021
The vulnerability described in CVE-2011-3638 resides within the ext4 filesystem implementation of the Linux kernel, specifically in the fs/ext4/extents.c file. This flaw represents a critical issue in how the kernel handles extent management during filesystem operations, particularly when dealing with extent splitting scenarios. The vulnerability affects Linux kernel versions prior to 3.0 and demonstrates a fundamental failure in the filesystem's dirty page tracking mechanism that can lead to system instability and potential denial of service conditions.
The technical root cause of this vulnerability stems from an insufficient dirty page marking mechanism during extent splitting operations. When the ext4 filesystem encounters situations where extents need to be split, the kernel fails to properly mark modified extents as dirty in certain conditional cases. This oversight creates a scenario where changes made to filesystem metadata during extent operations are not properly synchronized to persistent storage. The issue manifests specifically during ext4 unmount and mount operations, where the filesystem's internal state becomes inconsistent due to the failure to track modified extents properly. This condition creates a race between the filesystem's metadata management and its dirty page tracking system, leading to potential data corruption scenarios that ultimately result in system crashes.
The operational impact of this vulnerability extends beyond simple system crashes, as it represents a serious reliability issue that can compromise the integrity of ext4 filesystems. Local attackers can exploit this weakness to systematically cause denial of service conditions by performing operations that trigger the problematic extent splitting code paths. The vulnerability's exploitation requires local access but can result in complete system instability, making it particularly dangerous in multi-user environments where unprivileged users might have access to filesystem operations. The flaw essentially creates a condition where the filesystem's internal consistency checks fail during critical operations, leading to kernel panics and system reboots that can disrupt services and potentially cause data loss.
From a cybersecurity perspective, this vulnerability aligns with CWE-119, which addresses "Improper Access to Memory" and represents a failure in memory management during filesystem operations. The issue also relates to ATT&CK technique T1490, which covers "Inhibit System Recovery" through filesystem corruption or manipulation. The vulnerability demonstrates poor adherence to the principle of least privilege and proper resource management in kernel space operations. Organizations should implement immediate patching strategies to address this vulnerability, as it represents a known exploit vector that can be leveraged to disrupt system availability. The recommended mitigation involves upgrading to Linux kernel version 3.0 or later, where the extent dirty page tracking has been properly implemented to prevent the described condition. Additionally, system administrators should monitor filesystem operations that might trigger extent splitting scenarios and implement proper logging to detect potential exploitation attempts. The vulnerability underscores the critical importance of proper kernel memory management and the potential consequences of inadequate dirty page tracking in filesystem implementations, making it a prime example of how seemingly minor implementation flaws can result in significant system reliability issues.