CVE-2021-47481 is a vulnerability identified in the Linux kernel's RDMA (Remote Direct Memory Access) subsystem, specifically within the mlx5 driver which supports Mellanox ConnectX-5 network adapters. The issue arises from improper initialization of the On-Demand Paging (ODP) xarray when creating an ODP Memory Region (MR). Normally, zero-filling memory would mask this missing initialization, but an erroneous assignment to the desc_size variable in the reg_create() function leads to a kernel crash due to an unhandled page fault. This fault occurs when the mlx5_ib_dereg_mr() function attempts to deregister a memory region, triggering a BUG and kernel oops, which results in a denial of service (system crash or hang). The vulnerability is rooted in a logic error in the mlx5_ib driver code, where the ODP xarray is not properly initialized before use, causing invalid memory access. The provided stack trace shows the crash occurs in kernel space during RDMA operations, specifically when user-space applications interact with the ib_uverbs interface to deregister memory regions. This vulnerability affects Linux kernel versions containing the specified commits prior to the fix, and it is relevant for systems using Mellanox hardware with RDMA capabilities. No known exploits are reported in the wild as of the publication date, and no CVSS score has been assigned. The fix involves adding the missing xarray initialization and removing the incorrect desc_size assignment to prevent the crash.

For European organizations, the impact of CVE-2021-47481 primarily concerns systems that utilize RDMA technology, especially those deploying Mellanox ConnectX-5 network adapters in high-performance computing (HPC), data centers, or cloud infrastructure. The vulnerability can cause kernel crashes leading to denial of service, which disrupts critical applications relying on low-latency, high-throughput networking. This can affect financial institutions, research centers, telecommunications providers, and cloud service operators that depend on stable RDMA-enabled Linux servers. While the vulnerability does not appear to allow privilege escalation or remote code execution, the resulting system instability can cause operational downtime, data processing delays, and potential loss of availability for services. Given the specialized nature of RDMA hardware, the scope is limited to environments using this technology, but the impact on availability in these contexts can be significant. Additionally, the lack of known exploits reduces immediate risk, but unpatched systems remain vulnerable to accidental crashes or potential future exploit development.

European organizations should take the following specific steps to mitigate CVE-2021-47481: 1) Identify Linux systems running kernels with the affected mlx5_ib driver versions, especially those using Mellanox ConnectX-5 or similar RDMA hardware. 2) Apply the official Linux kernel patches that initialize the ODP xarray correctly and remove the erroneous desc_size assignment as soon as they become available from trusted Linux distributions or kernel maintainers. 3) For environments where immediate patching is not feasible, consider disabling RDMA functionality or the mlx5_ib driver temporarily to prevent triggering the vulnerability, understanding this may impact performance. 4) Monitor kernel logs and system stability closely for signs of crashes related to ib_write_bw or ib_uverbs ioctl calls, which may indicate attempts to trigger the bug. 5) Incorporate this vulnerability into vulnerability management and incident response processes to ensure timely detection and remediation. 6) Engage with hardware vendors and Linux distribution providers for guidance and updates on patches and mitigations specific to their platforms.