CVE-2021-47392 is a vulnerability identified in the Linux kernel's RDMA (Remote Direct Memory Access) subsystem, specifically within the RDMA Connection Manager (rdma_cm) component. The issue arises in the function cma_listen_on_all(), which is responsible for setting up listeners on all devices for RDMA connections. When cma_listen_on_all() fails, it leaves per-device IDs on the listen_list without updating their state to RDMA_CM_ADDR_BOUND. This incorrect state prevents the proper invocation of cma_cancel_listens() during the destruction of the connection manager ID (cmid). As a result, the per-device IDs retain their reference counts and are not destroyed, leading to a deadlock scenario. The deadlock manifests as a blocked task waiting indefinitely, as shown in the provided kernel stack trace, which includes scheduling and destruction functions related to RDMA connection management. The root cause is a lack of atomic rollback or cleanup under the lock when cma_listen_on_all() encounters an error. This flaw can cause resource leaks and kernel deadlocks, potentially impacting system stability and availability. The vulnerability affects specific Linux kernel versions identified by commit hashes, and although no known exploits are reported in the wild, the issue is critical for environments utilizing RDMA for high-performance networking. The fix involves ensuring that cma_listen_on_all() properly unwinds its actions atomically under the lock during failure to prevent stale references and deadlocks.

For European organizations, especially those operating data centers, HPC clusters, or financial trading platforms that rely on RDMA for low-latency, high-throughput networking, this vulnerability poses a significant risk to system availability and reliability. A deadlock in the kernel can cause service interruptions, requiring system reboots or manual intervention, which could lead to downtime and operational disruption. Organizations in sectors such as finance, research, telecommunications, and cloud service providers that deploy Linux servers with RDMA-enabled hardware are particularly vulnerable. The impact extends to any critical infrastructure relying on Linux kernels with affected versions, potentially affecting service-level agreements and causing financial and reputational damage. While the vulnerability does not directly expose confidentiality or integrity risks, the availability impact alone is substantial in environments where uptime and performance are critical.

European organizations should prioritize updating their Linux kernels to versions where this vulnerability is patched. Since the issue is related to specific commit versions, applying the latest stable kernel updates from trusted Linux distributions is essential. For environments where immediate patching is not feasible, administrators should consider disabling RDMA services or the rdma_cm module temporarily to mitigate the risk of deadlocks. Monitoring kernel logs for symptoms of deadlocks or resource leaks related to RDMA can help detect exploitation attempts or manifestation of the issue. Additionally, implementing robust kernel crash recovery and automated reboot mechanisms can reduce downtime impact. Organizations should also audit their RDMA usage and configurations to ensure minimal exposure. Engaging with hardware vendors for firmware and driver updates that complement kernel patches is advisable. Finally, thorough testing in staging environments before deploying patches in production will help avoid unintended disruptions.