CVE-2024-46789 is a vulnerability identified in the Linux kernel's memory management subsystem, specifically within the slab allocator code under certain kernel configurations. The issue arises when the kernel is compiled with CONFIG_MEMCG (memory control groups), CONFIG_KFENCE (Kernel Electric Fence), and CONFIG_KMEMLEAK (kernel memory leak detector) enabled simultaneously. The vulnerability is related to improper handling of slab object extensions (obj_exts) during memory allocation and deallocation. In this scenario, when kfence allocation succeeds, the slab's obj_exts field is non-empty because it is initialized during kfence pool setup. However, due to a missing check in the alloc_tagging_slab_free_hook function, the reference count (ref->ct) remains NULL because the alloc_tag_add function is not called. Later, when mem_pool_free is invoked, the presence of obj_exts triggers the alloc_tag_sub function, which expects alloc_tag to be set. Since it is not, a kernel warning is generated, indicating a potential inconsistency in memory tagging and freeing logic. The kernel warning includes a stack trace pointing to kmem_cache_free and related functions, highlighting the problem during slab memory free operations. This flaw does not appear to be exploitable for privilege escalation or arbitrary code execution but can lead to kernel warnings and potential instability or denial of service due to unexpected kernel behavior. The patch involves adding appropriate checks in alloc_tagging_slab_free_hook to handle these conditions correctly. The vulnerability is specific to certain kernel configurations and versions, and no known exploits are reported in the wild as of the publication date.

For European organizations, the impact of CVE-2024-46789 is primarily related to system stability and reliability rather than direct compromise or data breach. Systems running Linux kernels compiled with the affected configurations (CONFIG_MEMCG, CONFIG_KFENCE, CONFIG_KMEMLEAK) may experience kernel warnings and potential crashes or hangs during memory deallocation in slab allocators. This can affect servers, virtual machines, and embedded devices relying on these kernel features for memory debugging and leak detection. Organizations using such kernels in production environments, especially those with high availability requirements, could face service interruptions or degraded performance. Although no direct exploitation for privilege escalation is known, the kernel warnings and potential instability could be leveraged by attackers to cause denial of service conditions. This is particularly relevant for cloud providers, data centers, and critical infrastructure operators in Europe that use Linux extensively. The vulnerability also affects development and testing environments where these kernel debugging features are enabled, potentially impacting software quality assurance processes.

European organizations should take the following specific mitigation steps: 1) Identify Linux systems running kernels with CONFIG_MEMCG, CONFIG_KFENCE, and CONFIG_KMEMLEAK enabled, especially those in production or critical environments. 2) Apply the official Linux kernel patches that address CVE-2024-46789 as soon as they become available from trusted sources or Linux distribution vendors. 3) If immediate patching is not feasible, consider disabling one or more of the involved kernel features (KFENCE or KMEMLEAK) temporarily to avoid triggering the vulnerability, balancing this against the loss of debugging capabilities. 4) Monitor kernel logs for the specific warning message "alloc_tag was not set" or related stack traces to detect if the issue is occurring in deployed systems. 5) For virtualized environments, ensure hypervisor and guest kernel versions are updated to avoid cascading instability. 6) Incorporate this vulnerability into vulnerability management and patching workflows, prioritizing systems where memory debugging features are enabled. 7) Engage with Linux distribution security advisories and subscribe to relevant mailing lists to receive timely updates on patches and mitigations.