CVE-2021-47504 is a vulnerability identified in the Linux kernel's io_uring subsystem, which is a high-performance asynchronous I/O interface introduced to improve efficiency and scalability of I/O operations. The vulnerability arises from improper handling of task_work during cancellation of work items. Specifically, when a work item is successfully canceled but still requires processing via task_work, the kernel can enter an uninterruptible sleep state within the io_uring_cancel_generic() function. This occurs because the task_work is not executed as part of the cancellation process, causing the system to hang indefinitely waiting for the work item to complete. This results in a lack of forward progress and triggers uninterruptible sleep warnings. The issue is rooted in the kernel's failure to ensure that task_work callbacks are run during cancellation, which is critical for cleaning up and completing asynchronous tasks properly. The vulnerability does not appear to have any known exploits in the wild as of the published date, and no CVSS score has been assigned. The fix involves ensuring that task_work is executed as part of the cancellation routine, preventing the kernel from entering an uninterruptible sleep state. This vulnerability affects Linux kernel versions identified by the commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, indicating a specific patch or code state. The vulnerability is technical in nature and primarily impacts system stability and availability rather than confidentiality or integrity directly. However, prolonged uninterruptible sleeps can lead to denial of service conditions on affected systems.

For European organizations, this vulnerability poses a risk primarily to system availability and reliability, especially for those relying on Linux servers running workloads that utilize io_uring for asynchronous I/O operations. Industries with high dependency on Linux infrastructure, such as telecommunications, finance, cloud service providers, and critical infrastructure operators, may experience service disruptions or degraded performance if affected systems enter uninterruptible sleep states. This can lead to denial of service conditions, impacting business continuity and operational efficiency. Although there is no evidence of exploitation in the wild, the vulnerability's presence in kernel-level code means that attackers with local access could potentially trigger system hangs, affecting multi-tenant environments or shared hosting services common in European data centers. The impact is more pronounced in environments where high availability is critical and where kernel-level stability issues can cascade into broader service outages. Confidentiality and integrity impacts are minimal or indirect, but availability degradation can have significant operational and reputational consequences.

European organizations should prioritize patching Linux kernels to versions that include the fix for CVE-2021-47504. This involves updating to the latest stable kernel releases provided by their Linux distribution vendors, ensuring that the io_uring subsystem handles task_work cancellations correctly. System administrators should audit their environments to identify systems using io_uring, particularly those running workloads with asynchronous I/O patterns. Monitoring for uninterruptible sleep warnings in system logs (e.g., kernel messages indicating 'D' state processes) can help detect potential issues related to this vulnerability. In environments where immediate patching is not feasible, organizations can consider temporarily disabling io_uring functionality if supported by their kernel configuration, though this may impact performance. Additionally, implementing strict access controls to limit local user access can reduce the risk of exploitation, as triggering the vulnerability requires local interaction with the kernel's io_uring interface. Regular kernel updates and proactive system health monitoring are essential to mitigate risks from this and similar kernel-level vulnerabilities.