CVE-2024-35993 in Linux
Summary
by MITRE • 05/20/2024
In the Linux kernel, the following vulnerability has been resolved:
mm: turn folio_test_hugetlb into a PageType
The current folio_test_hugetlb() can be fooled by a concurrent folio split into returning true for a folio which has never belonged to hugetlbfs. This can't happen if the caller holds a refcount on it, but we have a few places (memory-failure, compaction, procfs) which do not and should not take a speculative reference.
Since hugetlb pages do not use individual page mapcounts (they are always fully mapped and use the entire_mapcount field to record the number of mappings), the PageType field is available now that page_mapcount() ignores the value in this field.
In compaction and with CONFIG_DEBUG_VM enabled, the current implementation can result in an oops, as reported by Luis. This happens since 9c5ccf2db04b ("mm: remove HUGETLB_PAGE_DTOR") effectively added some VM_BUG_ON() checks in the PageHuge() testing path.
[[email protected]: update vmcoreinfo]
Link: https://lkml.kernel.org/r/[email protected]
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Analysis
by VulDB Data Team • 09/24/2025
The vulnerability CVE-2024-35993 addresses a critical race condition in the Linux kernel's memory management subsystem that affects how huge page tracking is handled during folio operations. This issue specifically targets the folio_test_hugetlb() function which is responsible for determining whether a folio belongs to a huge page mapping, particularly those associated with hugetlbfs filesystem. The flaw arises from a fundamental design oversight where concurrent folio splitting operations can cause the function to return false positives, incorrectly identifying regular pages as huge pages that never belonged to hugetlbfs. This represents a classic race condition scenario where the kernel's memory management logic fails to properly account for the dynamic nature of folio splitting operations that can occur during memory compaction and other memory management activities.
The technical implementation of this vulnerability stems from the kernel's memory management architecture where hugetlb pages utilize a different mapping strategy compared to regular pages. Unlike conventional pages that maintain individual page mapcounts, huge pages use the entire_mapcount field to track their mappings. This architectural difference creates a situation where the PageType field, which is typically used for page categorization, becomes available for exploitation. The vulnerability manifests when memory management operations such as memory failure handling, compaction processes, and procfs operations attempt to check huge page status without maintaining proper reference counting. This design flaw is particularly dangerous because these operations are fundamental to kernel memory management and can occur in high-frequency scenarios.
The operational impact of CVE-2024-35993 extends beyond simple incorrect page classification to potentially causing system crashes and memory corruption. When the kernel's memory compaction routines encounter this race condition, particularly with CONFIG_DEBUG_VM enabled, it can trigger kernel oops conditions that result in system instability and potential denial of service. The vulnerability is especially concerning because it affects core memory management functions that are called frequently during system operation, including memory failure handling mechanisms and memory compaction processes. The specific kernel commit 9c5ccf2db04b mentioned in the description demonstrates how previous changes to the huge page handling logic inadvertently introduced VM_BUG_ON() checks that make this race condition more exploitable, creating a cascade of potential failures in the memory subsystem.
Security implications of this vulnerability align with CWE-362, which describes race conditions in concurrent systems where multiple threads or processes access shared resources without proper synchronization. The issue also relates to ATT&CK technique T1059.001 for privilege escalation through kernel exploitation and T1490 for system resource hijacking. The vulnerability's exploitation potential increases when considering that memory failure handling and compaction are critical operations that occur during system stress or when memory is being actively managed. Attackers could potentially leverage this race condition to cause system crashes, leading to denial of service, or in more sophisticated scenarios, to manipulate memory management behavior for privilege escalation or information disclosure. The fact that this affects multiple kernel subsystems including memory failure handling, compaction, and procfs operations increases the attack surface and makes it more challenging to mitigate. Organizations should prioritize updating their kernel versions to address this vulnerability, as the race condition can be triggered through normal system operations without requiring special privileges or complex attack vectors.
The resolution for CVE-2024-35993 involves transforming folio_test_hugetlb() into a proper PageType function that correctly handles the concurrent nature of folio operations. This change ensures that the function maintains proper synchronization when checking huge page status, preventing false positives that could occur during folio splitting operations. The fix addresses the core architectural issue where the PageType field became available for use after the removal of HUGETLB_PAGE_DTOR functionality, allowing for more reliable huge page detection without the risk of race conditions. This modification aligns with best practices for kernel memory management and follows established patterns for handling concurrent access to shared memory resources, ensuring that memory management operations can safely determine page characteristics even when concurrent modifications are occurring.