CVE-2021-46919 in Linux
Summary
by MITRE • 02/27/2024
In the Linux kernel, the following vulnerability has been resolved:
dmaengine: idxd: fix wq size store permission state
WQ size can only be changed when the device is disabled. Current code allows change when device is enabled but wq is disabled. Change the check to detect device state.
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Analysis
by VulDB Data Team • 02/27/2024
The vulnerability identified as CVE-2021-46919 resides within the Linux kernel's dmaengine subsystem, specifically affecting the Intel In-Driver DMA (idxd) driver implementation. This flaw represents a privilege escalation opportunity through improper state validation during device configuration operations. The issue manifests when attempting to modify the work queue (wq) size parameter, which is a critical configuration element for DMA device operation. The vulnerability stems from inadequate device state checking that permits modifications to wq size even when the device remains in an enabled state, despite the underlying requirement that such changes should only be permissible when the device is fully disabled. This misconfiguration creates a potential attack surface where malicious actors could manipulate DMA device parameters during active operation, potentially leading to system instability or unauthorized access to hardware resources.
The technical root cause of this vulnerability aligns with CWE-691, which addresses insufficient control of a resource through a mechanism that allows access to a resource that should be restricted. The flaw occurs within the idxd driver's permission handling logic where the code fails to properly validate the device's operational state before allowing wq size modifications. The current implementation incorrectly permits wq size changes when the device is enabled but the work queue itself is disabled, violating the fundamental principle that device configuration parameters requiring hardware-level changes should only be modifiable during specific operational states. This improper state validation creates a condition where the driver's internal state management becomes inconsistent with the actual hardware configuration, potentially leading to race conditions or memory corruption issues during concurrent access scenarios.
From an operational impact perspective, this vulnerability could enable attackers to manipulate DMA device behavior in ways that compromise system integrity and security. The ability to modify wq size parameters while the device remains operational could potentially disrupt legitimate DMA operations, cause data corruption, or provide a foothold for further exploitation. Attackers might leverage this flaw to gain elevated privileges by manipulating the device's operational parameters, particularly in environments where DMA operations are used for high-performance data transfer or system-level operations. The vulnerability is particularly concerning in server environments where DMA devices are frequently utilized for network and storage I/O operations, as it could potentially be exploited to disrupt critical system services or establish persistent access to hardware resources.
The mitigation strategy for CVE-2021-46919 involves implementing proper device state validation within the idxd driver's configuration handling code. System administrators should ensure that all Linux kernel updates containing the fix are applied promptly, as the vulnerability requires a kernel-level patch to resolve the improper state checking logic. The fix enforces that wq size modifications can only occur when the device is completely disabled, preventing the scenario where device state and configuration parameters become misaligned. Organizations should also consider implementing monitoring for unusual DMA device configuration changes and establish baseline operational states for DMA devices to detect potential exploitation attempts. This vulnerability demonstrates the importance of proper resource state management in kernel drivers and aligns with ATT&CK technique T1068, which covers the exploitation of legitimate credentials and system access for privilege escalation, particularly in the context of kernel-level privilege escalation through device driver manipulation.