CVE-2022-48802 is a vulnerability in the Linux kernel related to the handling of memory management information exposed via the /proc filesystem, specifically in the task_mmu.c component. The issue arises from a race condition triggered when reading the /proc/$PID/smaps file concurrently with a MADV_FREE system call that may split Transparent Huge Pages (THPs). The vulnerability manifests as a kernel BUG due to an invalid opcode triggered by an inconsistent state in page reference counting. The root cause is that during the smaps walk, the kernel reads the mapcount of a page, but if MADV_FREE concurrently splits a THP, the page is no longer a tail page, causing the PageDoubleMap() check to fail and triggering a kernel crash. The problem is exacerbated by the fact that the mapcount function does not properly handle migration entries, leading to incorrect reference counting and a race condition. The fix involves modifying smaps_account() to recognize migration entries and skip calling page_mapcount() for them, while still correctly handling device private entries. Additionally, a similar issue in pagemap was fixed preemptively. This vulnerability was discovered and reported by syzbot, an automated kernel fuzzer, and affects Linux kernel versions around 5.16.0-rc6. The vulnerability does not have a CVSS score yet and is not known to be exploited in the wild. The technical details indicate that the flaw can cause kernel panics or crashes when user-space processes read memory mapping information concurrently with memory advice calls that manipulate huge pages.

For European organizations, this vulnerability poses a risk primarily to systems running vulnerable Linux kernel versions, especially those using Transparent Huge Pages and exposing /proc/$PID/smaps information. The impact includes potential denial of service (DoS) due to kernel crashes, which can disrupt critical services, especially in environments relying on Linux servers for infrastructure, cloud services, and container orchestration. While the vulnerability does not directly lead to privilege escalation or data leakage, the induced kernel panic can cause service outages and potential data loss if systems are not properly protected or if critical processes are affected. Organizations with high availability requirements, such as financial institutions, healthcare providers, and critical infrastructure operators in Europe, could face operational disruptions. Additionally, the vulnerability could be leveraged as part of a multi-stage attack to degrade system reliability or to cause targeted disruptions in cloud environments. Since the vulnerability is triggered by specific concurrent operations, exploitation requires local access and specific conditions, limiting remote exploitation but still posing a risk in multi-tenant or shared environments common in European data centers.

European organizations should prioritize updating their Linux kernels to versions where this vulnerability is patched, ideally applying the fix that modifies smaps_account() to handle migration entries correctly. System administrators should audit their Linux kernel versions and plan immediate upgrades or backport patches from trusted sources. For environments where immediate patching is not feasible, mitigating the risk involves restricting unprivileged users from accessing /proc/$PID/smaps or limiting the use of MADV_FREE calls, especially in multi-tenant or containerized environments. Monitoring kernel logs for BUG reports related to page flags or invalid opcode errors can help detect attempts to trigger this vulnerability. Additionally, organizations should review their use of Transparent Huge Pages and consider disabling or tuning THP behavior if it aligns with their performance requirements and security posture. Since the vulnerability requires concurrent operations, implementing strict process isolation and limiting user privileges can reduce the attack surface. Finally, integrating kernel crash monitoring and automated recovery mechanisms will help minimize downtime in case of exploitation.