CVE-2010-2226 in Linux
Summary
by MITRE
The xfs_swapext function in fs/xfs/xfs_dfrag.c in the Linux kernel before 2.6.35 does not properly check the file descriptors passed to the SWAPEXT ioctl, which allows local users to leverage write access and obtain read access by swapping one file into another file.
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Analysis
by VulDB Data Team • 09/24/2021
The vulnerability described in CVE-2010-2226 represents a critical access control flaw within the Linux kernel's XFS filesystem implementation that existed prior to kernel version 2.6.35. This issue stems from improper validation of file descriptors during the execution of the SWAPEXT ioctl operation, which is designed to swap extents between files. The flaw allows local attackers with write permissions on a file to manipulate the filesystem in a manner that grants them unauthorized read access to other files within the same filesystem, effectively bypassing the normal file permission model. The vulnerability specifically affects the xfs_swapext function located in fs/xfs/xfs_dfrag.c, where the kernel fails to adequately verify the integrity and legitimacy of file descriptors passed to the ioctl command.
The technical exploitation of this vulnerability relies on the ability of a local user to execute the SWAPEXT ioctl with maliciously crafted file descriptor parameters. When the xfs_swapext function processes these parameters without proper validation, it creates a condition where the kernel can be tricked into reading data from one file and writing it into another file, effectively enabling read operations on files that the user normally lacks permission to access. This occurs because the kernel's validation mechanism fails to ensure that both file descriptors refer to legitimate files within the same filesystem or that the user possesses the appropriate permissions for both operations. The flaw essentially creates a privilege escalation path within the filesystem layer, allowing attackers to circumvent standard file access controls through manipulation of the underlying storage operations.
From an operational standpoint, this vulnerability poses significant risks to systems running affected kernel versions, as it enables local users to potentially access sensitive data that should be restricted to authorized personnel only. The impact extends beyond simple data theft, as it can potentially expose system configuration files, user credentials, or other confidential information stored within the same filesystem. The vulnerability is particularly concerning because it operates at the kernel level within the filesystem driver, making it difficult to detect through standard application-level security measures. Security researchers have categorized this issue as a privilege escalation vulnerability that aligns with CWE-284, which addresses improper access control in software systems, and it can be mapped to ATT&CK technique T1068, which covers local privilege escalation through kernel exploits.
The recommended mitigation strategy involves upgrading to Linux kernel version 2.6.35 or later, where the vulnerability has been patched through proper validation of file descriptors within the xfs_swapext function. System administrators should also implement additional monitoring and access control measures to detect unauthorized file system operations, particularly those involving ioctl commands. The patch addresses the root cause by ensuring that the kernel validates file descriptor integrity before proceeding with extent swapping operations, preventing malicious users from manipulating file access permissions through the SWAPEXT ioctl. Organizations should conduct thorough vulnerability assessments to identify systems running affected kernel versions and prioritize patch deployment to maintain system integrity and protect against potential exploitation of this access control flaw.