CVE-2024-53096: Vulnerability in Linux Linux

Severity: mediumType: vulnerabilityCVE-2024-53096

In the Linux kernel, the following vulnerability has been resolved: mm: resolve faulty mmap_region() error path behaviour The mmap_region() function is somewhat terrifying, with spaghetti-like control flow and numerous means by which issues can arise and incomplete state, memory leaks and other unpleasantness can occur. A large amount of the complexity arises from trying to handle errors late in the process of mapping a VMA, which forms the basis of recently observed issues with resource leaks and observable inconsistent state. Taking advantage of previous patches in this series we move a number of checks earlier in the code, simplifying things by moving the core of the logic into a static internal function __mmap_region(). Doing this allows us to perform a number of checks up front before we do any real work, and allows us to unwind the writable unmap check unconditionally as required and to perform a CONFIG_DEBUG_VM_MAPLE_TREE validation unconditionally also. We move a number of things here: 1. We preallocate memory for the iterator before we call the file-backed memory hook, allowing us to exit early and avoid having to perform complicated and error-prone close/free logic. We carefully free iterator state on both success and error paths. 2. The enclosing mmap_region() function handles the mapping_map_writable() logic early. Previously the logic had the mapping_map_writable() at the point of mapping a newly allocated file-backed VMA, and a matching mapping_unmap_writable() on success and error paths. We now do this unconditionally if this is a file-backed, shared writable mapping. If a driver changes the flags to eliminate VM_MAYWRITE, however doing so does not invalidate the seal check we just performed, and we in any case always decrement the counter in the wrapper. We perform a debug assert to ensure a driver does not attempt to do the opposite. 3. We also move arch_validate_flags() up into the mmap_region() function. This is only relevant on arm64 and sparc64, and the check is only meaningful for SPARC with ADI enabled. We explicitly add a warning for this arch if a driver invalidates this check, though the code ought eventually to be fixed to eliminate the need for this. With all of these measures in place, we no longer need to explicitly close the VMA on error paths, as we place all checks which might fail prior to a call to any driver mmap hook. This eliminates an entire class of errors, makes the code easier to reason about and more robust.

AI Analysis

Technical Summary

CVE-2024-53096 addresses a vulnerability in the Linux kernel's memory management subsystem, specifically within the mmap_region() function. This function is responsible for managing virtual memory area (VMA) mappings, which are critical for processes to access files and memory regions. The vulnerability stems from complex and error-prone control flow in mmap_region(), which previously allowed inconsistent states, resource leaks, and incomplete error handling during memory mapping operations. The patch restructures the code by moving key checks earlier in the execution path and consolidating core logic into a static internal function __mmap_region(). This redesign enables preallocation of memory for iterators before invoking file-backed memory hooks, allowing early exits on errors without complicated cleanup. Additionally, the handling of writable mappings has been unified to perform mapping_map_writable() and mapping_unmap_writable() operations unconditionally for file-backed shared writable mappings, preventing mismatches and potential resource mismanagement. Architecture-specific validations, such as arch_validate_flags() for arm64 and sparc64, have been moved up to ensure early detection of invalid flags, with warnings added for SPARC with ADI enabled. Overall, these changes eliminate a class of errors related to resource leaks and inconsistent VMA states, improving robustness and maintainability of the Linux kernel's memory management. No known exploits are reported in the wild, and the vulnerability does not have an assigned CVSS score yet.

Potential Impact

For European organizations, this vulnerability could lead to resource leaks and inconsistent memory states in Linux systems, potentially causing system instability, degraded performance, or denial of service conditions. Since Linux is widely used in servers, cloud infrastructure, and embedded devices across Europe, exploitation could disrupt critical services, especially in sectors relying on high availability such as finance, telecommunications, healthcare, and government. Although no active exploits are known, the complexity of the mmap_region() function and the nature of the bug could allow attackers with local access to trigger resource exhaustion or kernel crashes, impacting confidentiality and availability. Systems running customized or older Linux kernel versions without the patch are at higher risk. The vulnerability's impact is primarily on system stability and reliability rather than direct privilege escalation or remote code execution, but it could be leveraged as part of a multi-stage attack chain.

Mitigation Recommendations

European organizations should prioritize updating Linux kernels to versions containing the fix for CVE-2024-53096 as soon as patches are available from their distributions or vendors. Kernel updates should be tested in staging environments to ensure compatibility with existing workloads. Organizations should audit their infrastructure to identify all Linux systems, including embedded devices and containers, to ensure comprehensive patch deployment. For systems where immediate patching is not feasible, monitoring kernel logs and system resource usage for signs of memory leaks or abnormal behavior is recommended. Additionally, restricting local user access and enforcing strict privilege separation can reduce the risk of exploitation. Developers and maintainers of custom kernel modules or drivers should review their code for compliance with the new mmap_region() logic, especially regarding writable shared mappings and architecture-specific flag validations, to avoid introducing regressions or incompatibilities. Employing runtime security tools that monitor kernel integrity and memory management anomalies can provide early detection of exploitation attempts.