CVE-2024-56544 is a vulnerability identified in the Linux kernel's udmabuf subsystem, which handles user-space DMA buffer allocations. The core issue arises from the way the udmabuf driver manages large memory allocations using the kmalloc allocator. Specifically, when running on 64-bit machines with a PAGE_SIZE of 4096 bytes and a MAX_PAGE_ORDER of 10, the kmalloc allocator can only reliably allocate up to 4MB of contiguous memory (4096 bytes * 2^10). Attempts to allocate memory beyond this limit, such as a 3GB udmabuf buffer, result in allocation failures and kernel warnings due to fragmentation and allocator limitations. The vulnerability manifests as a kernel warning and failure to create large udmabuf buffers, which can lead to denial of service conditions or instability in applications relying on large DMA buffers. The root cause is that the udmabuf driver uses kmalloc for its folios array, which is limited by MAX_PAGE_ORDER and memory fragmentation. The patch changes the allocation method from kmalloc to kvmalloc_array, which can fallback to vmalloc if contiguous physical memory is unavailable. vmalloc allocates virtually contiguous memory, allowing for larger allocations without fragmentation issues, thus resolving the problem. This fix ensures that large udmabuf buffers can be allocated reliably without triggering kernel warnings or allocation failures. No known exploits are currently reported in the wild, and the vulnerability primarily affects systems that attempt to allocate very large DMA buffers via udmabuf on affected Linux kernel versions. The vulnerability does not appear to allow privilege escalation or arbitrary code execution but can cause denial of service or application failures due to allocation errors.

For European organizations, the impact of CVE-2024-56544 is primarily related to system stability and availability, particularly in environments that utilize Linux-based systems for high-performance computing, embedded systems, or specialized hardware interfacing that relies on large DMA buffers. Industries such as telecommunications, automotive, industrial automation, and scientific research in Europe often deploy Linux kernels with udmabuf for direct memory access operations. Failure to allocate large buffers could lead to application crashes, degraded performance, or denial of service conditions, potentially disrupting critical services or production environments. While this vulnerability does not directly compromise confidentiality or integrity, the resulting instability could indirectly affect operational continuity and service reliability. Organizations running custom or older Linux kernels that have not incorporated the patch are at risk. Additionally, systems with high memory demands or those performing large-scale data transfers using DMA buffers are more susceptible. The absence of known exploits reduces immediate risk, but unpatched systems remain vulnerable to accidental or malicious triggering of the allocation failure, which could be leveraged in targeted denial of service attacks.

To mitigate CVE-2024-56544, European organizations should: 1) Apply the official Linux kernel patch that replaces kmalloc with kvmalloc_array for udmabuf allocations, ensuring fallback to vmalloc for large memory requests. This patch is critical to prevent allocation failures and kernel warnings. 2) Update Linux kernel versions to the latest stable releases that include this fix, especially on systems that utilize udmabuf or perform large DMA buffer allocations. 3) Audit and monitor systems for kernel warnings related to __alloc_pages and udmabuf allocation failures, which may indicate attempts to trigger this vulnerability. 4) For environments using custom kernel builds, verify that the memory allocation strategy for udmabuf matches the patched approach. 5) Limit the maximum size of udmabuf allocations where possible to avoid unnecessarily large memory requests that could exacerbate fragmentation issues. 6) Implement robust system monitoring and alerting to detect abnormal kernel warnings or crashes related to memory allocation. 7) Engage with hardware and software vendors to confirm compatibility and patch availability for embedded or specialized Linux distributions. These targeted steps go beyond generic advice by focusing on the specific allocator change and operational monitoring relevant to this vulnerability.