CVE-2021-46919 is a vulnerability identified in the Linux kernel's dmaengine subsystem, specifically related to the Intel Data Streaming Accelerator (idxd) driver. The issue concerns improper permission checks when modifying the work queue (WQ) size. The Linux kernel code allowed changes to the WQ size even when the device was enabled but the work queue itself was disabled. According to the intended design, the WQ size should only be modifiable when the device is fully disabled to prevent inconsistent or unsafe state changes. This vulnerability arises because the existing check did not correctly verify the device's enabled state, allowing a potential attacker with sufficient privileges to alter the WQ size in an unintended state. Although the vulnerability does not appear to have known exploits in the wild, it could lead to system instability or unexpected behavior in the DMA engine, which is critical for high-performance data transfers. The fix involves changing the permission check to correctly detect the device's state before allowing modifications to the WQ size, ensuring that changes are only permitted when the device is disabled. This vulnerability affects Linux kernel versions identified by the commit hash c52ca478233c172b2d322b5241d6279a8661cbba and possibly other versions containing the same flawed logic. Since the vulnerability is in a kernel subsystem, exploitation would require local access with privileges to interact with the dmaengine driver, limiting remote exploitation possibilities. However, improper handling of device states in kernel drivers can lead to privilege escalation or denial of service if exploited.

For European organizations, the impact of CVE-2021-46919 primarily concerns systems running Linux kernels with the vulnerable dmaengine idxd driver enabled, particularly in environments utilizing Intel Data Streaming Accelerator hardware for high-speed data processing. Potential impacts include system instability, crashes, or denial of service conditions caused by improper WQ size changes. In critical infrastructure sectors such as telecommunications, finance, and manufacturing, where Linux servers and embedded systems are prevalent, such instability could disrupt operations or degrade service availability. Although exploitation requires local privileged access, attackers who have already compromised a system could leverage this vulnerability to further destabilize or manipulate kernel behavior, potentially aiding in privilege escalation or evasion of security controls. European organizations relying on Linux-based servers, especially those using Intel accelerator hardware, should consider this vulnerability significant due to the kernel-level nature of the flaw and its potential to affect system reliability and security posture.

To mitigate CVE-2021-46919, European organizations should: 1) Apply the official Linux kernel patches that correct the device state check in the dmaengine idxd driver as soon as they become available from their Linux distribution vendors or upstream kernel sources. 2) Audit systems to identify those running vulnerable kernel versions with the idxd driver enabled, especially in environments utilizing Intel Data Streaming Accelerator hardware. 3) Restrict local access to trusted users only, as exploitation requires local privileges. 4) Implement strict access controls and monitoring on systems with the dmaengine subsystem to detect unusual activity or attempts to modify device states. 5) Consider disabling the idxd driver or related hardware acceleration features if not required, reducing the attack surface. 6) Maintain up-to-date system inventories and patch management processes to ensure timely deployment of kernel updates. 7) Conduct thorough testing of kernel updates in staging environments to prevent operational disruptions.