CVE-2026-74568 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
KVM: arm64: vgic: Fix race between LPI release and re-registration
Fix a potential race between decrementing an LPI's reference count and evicting that structure from the LPI xarray.
LPI structures are maintained in the VGIC LPI xarray (dist->lpi_xa). When the reference count of an LPI structure drops to zero, vgic_release_lpi_locked() removes the structure from the xarray and frees it under the xarray lock.
However, the release of an LPI can race with a concurrent LPI re-registration with the same INTID via vgic_add_lpi() on another CPU, since the reference count drop and the xarray eviction are not performed in a single atomic step. This can happen e.g. if the guest issues a DISCARD while the LPI is still referenced from a vCPU's active-pending list (ap_list), and the same INTID is re-mapped via MAPTI.
Particularly, vgic_release_lpi_locked() is called from two distinct paths: direct release via vgic_put_irq(), and deferred release via vgic_release_deleted_lpis(). During direct release, the issue can result in deleting a newly registered LPI from the xarray:
CPU0 (Releasing LPI) CPU1 (Adding new LPI) ==================== ===================== vgic_put_irq() __vgic_put_irq() refcount_dec_and_test() vgic_add_lpi() xa_lock_irqsave() old_irq = xa_load(.., intid) vgic_try_get_irq_ref(old_irq) == false new IRQ inserted --> __xa_store(.., intid, ..) xa_unlock_irqrestore() xa_lock_irqsave(); vgic_release_lpi_locked() __xa_erase(.., irq->intid) <-- BUG: new IRQ is erased kfree_rcu(old_irq)
During the deferred release path, the old IRQ can be leaked:
CPU0 (Releasing LPI) CPU1 (Adding new LPI) ==================== ===================== vgic_put_irq_norelease() __vgic_put_irq() refcount_dec_and_test() irq->pending_release = true vgic_add_lpi() xa_lock_irqsave() old_irq = xa_load(.., intid) vgic_try_get_irq_ref(oldirq) == false BUG: old IRQ overwritten --> __xa_store(.., intid, ..) xa_unlock_irqrestore()
vgic_release_deleted_lpis() xa_lock_irqsave() xa_for_each() { .. } <-- old IRQ with pending_release = true
is gone, so it cannot be released
To fix the direct release path, move the reference count drop inside the xarray lock, making sure that vgic_add_lpi() never encounters the to-be-released LPI.
In the deferred release path, the refcount drop must happen under a raw spinlock, so the xarray lock cannot be grabbed, and the same solution does not work. Instead, update vgic_add_lpi(), so that if it evicts an LPI from the xarray, it takes on the responsibility of freeing it. Consequently, an LPI may now be freed concurrently after a deferred release drops the refcount, so accessing the pending_release field is no longer safe from use-after-free. Delete all uses of the flag, and update vgic_release_deleted_lpis() to identify orphaned LPIs purely based on their refcount.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability described affects the Linux kernel's KVM implementation specifically on arm64 architecture within the Virtual Generic Interrupt Controller (VGIC) subsystem. This issue manifests as a race condition between the release and re-registration of Low Priority Interrupt (LPI) structures, which are managed in an xarray data structure known as dist->lpi_xa. The core problem arises when multiple CPU cores attempt concurrent operations on the same LPI identifier, leading to potential memory corruption or resource leaks.
The technical flaw stems from the lack of atomicity between reference count decrementing and xarray eviction operations for LPI structures. When an LPI's reference count reaches zero, the vgic_release_lpi_locked() function is invoked to remove and free the structure under the xarray lock protection. However, this process does not prevent a concurrent re-registration via vgic_add_lpi() from occurring between these two steps, creating a window where the newly registered LPI might be incorrectly removed from the xarray by the release operation or where an old LPI reference gets overwritten.
This vulnerability directly relates to CWE-362, which describes a race condition where multiple threads or processes access shared resources concurrently without proper synchronization. The issue can be exploited through malicious guest operating system behavior that triggers DISCARD operations while LPIs remain in active-pending lists, followed by re-mapping operations using MAPTI commands. The operational impact includes potential kernel crashes, memory corruption, and denial of service conditions that could affect the stability of virtualized environments.
The fix implements two distinct approaches to address different code paths. For direct release scenarios, the reference count decrement is moved inside the xarray lock, ensuring atomicity between reference management and structure eviction. This prevents the race condition where a newly registered LPI could be inadvertently deleted during the release process. In the deferred release path, which operates under different locking constraints, the solution modifies vgic_add_lpi() to assume responsibility for freeing evicted LPI structures rather than relying on the traditional reference counting approach. This change eliminates the use-after-free scenario that previously occurred when accessing the pending_release flag after concurrent operations.
The mitigation strategy aligns with ATT&CK technique T1499.001, which involves operating system binary proxies and kernel-level privilege escalation through exploitation of race conditions in memory management. By implementing proper atomic operations and restructuring the reference counting mechanism, the fix prevents unauthorized access patterns that could lead to privilege escalation or system compromise. The solution also addresses potential issues with memory management consistency as defined by the Linux kernel's memory management subsystem design principles, ensuring that virtual interrupt structures maintain their integrity during concurrent access scenarios.
The vulnerability demonstrates how complex synchronization mechanisms in hypervisor environments can create subtle race conditions that are difficult to detect through conventional testing methods. The fix requires careful consideration of both immediate and deferred execution paths while maintaining compatibility with existing kernel interfaces. This represents a common challenge in virtualization security where the abstraction layer between physical and virtual resources creates additional complexity for memory management and synchronization protocols.