CVE-2026-64438 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
crypto: qat - fix VF2PF work teardown race in adf_disable_sriov()
The VF2PF interrupt handler queues PF-side response work that stores a raw pointer to per-VF state (struct adf_accel_vf_info). Currently, adf_disable_sriov() destroys per-VF mutexes and frees vf_info without stopping new VF2PF work or waiting for in-flight workers to complete. A concurrently scheduled or already queued worker can then dereference freed memory.
This manifests as a use-after-free when KASAN is enabled:
BUG: KASAN: null-ptr-deref in mutex_lock+0x76/0xe0 Write of size 8 at addr 0000000000000260 by task kworker/24:2/... Workqueue: qat_pf2vf_resp_wq adf_iov_send_resp [intel_qat]
Call Trace: kasan_report+0x119/0x140 mutex_lock+0x76/0xe0 adf_gen4_pfvf_send+0xd4/0x1f0 [intel_qat]
adf_recv_and_handle_vf2pf_msg+0x290/0x360 [intel_qat]
adf_iov_send_resp+0x8c/0xe0 [intel_qat]
process_one_work+0x6ac/0xfd0 worker_thread+0x4dd/0xd30 kthread+0x326/0x410 ret_from_fork+0x33b/0x670
Add a PF-local flag, vf2pf_disabled, that gates work queueing, worker processing, and interrupt re-enabling during teardown. Set this flag atomically with the hardware interrupt mask inside adf_disable_all_vf2pf_interrupts(). After masking, synchronize the AE cluster MSI-X interrupt and flush the PF response workqueue before tearing down per-VF locks and state so all in-flight work completes before vf_info is destroyed.
Introduce adf_enable_all_vf2pf_interrupts() to clear the flag and unmask all VF2PF interrupts under the same lock when SR-IOV is re-enabled. This ensures the software flag and hardware state transition atomically on both the enable and disable paths.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability described represents a critical use-after-free condition within the Intel QuickAssist Technology (QAT) driver for Linux kernel versions that implement SR-IOV virtualization support. This issue specifically affects the qat_pf2vf_resp_wq workqueue processing mechanism in the adf_disable_sriov() function where concurrent access to freed memory structures can occur due to improper synchronization during virtual function teardown operations. The flaw stems from inadequate coordination between interrupt handling, work queue processing, and resource cleanup procedures that leads to a race condition scenario.
The technical root cause resides in how the VF2PF (Virtual Function to Physical Function) interrupt handler manages response work processing within the QAT acceleration framework. When a VF2PF message is received, the interrupt handler schedules work items on the qat_pf2vf_resp_wq workqueue that reference per-VF state information stored in struct adf_accel_vf_info structures. These structures contain raw pointers to memory regions that are freed during the teardown process without proper synchronization mechanisms to prevent new work from being queued or existing work from completing execution.
The vulnerability manifests through a classic use-after-free pattern where a worker thread attempts to access memory that has already been deallocated, resulting in kernel memory corruption and potential system instability. KASAN instrumentation reveals the exact sequence of events leading to the failure, showing that mutex_lock operations attempt to access freed memory at address 0x0000000000000260, which corresponds to a null pointer dereference during the adf_gen4_pfvf_send function execution. This demonstrates the fundamental flaw in the driver's teardown sequence where work items can execute against destroyed data structures.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable privilege escalation or denial-of-service conditions within systems utilizing QAT hardware acceleration with SR-IOV enabled. Attackers could exploit this race condition to either corrupt kernel memory leading to system crashes or potentially manipulate the execution flow to gain elevated privileges within the kernel context.
The mitigation strategy implemented addresses the core synchronization issues by introducing a new PF-local flag named vf2pf_disabled that serves as a gate mechanism controlling access to VF2PF work processing during teardown operations. This approach aligns with established best practices for concurrent programming and follows the principles outlined in CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and CWE-416 (Use After Free). The solution ensures atomic transitions between enabled and disabled states by coordinating software flags with hardware interrupt masking operations within a single critical section, preventing the race condition that allowed concurrent work processing against freed memory structures.
The fix establishes a comprehensive teardown sequence where the vf2pf_disabled flag is set atomically with hardware interrupt masking through the adf_disable_all_vf2pf_interrupts() function. This ensures that no new VF2PF work can be queued while existing work items complete before the per-VF state structures are destroyed. The synchronization includes waiting for all active AE cluster MSI-X interrupts to complete and flushing the PF response workqueue, guaranteeing that all in-flight work completes execution before memory deallocation occurs. Additionally, the solution introduces adf_enable_all_vf2pf_interrupts() function that maintains consistency by clearing the flag and re-enabling interrupts under the same lock context, ensuring atomic state transitions on both enable and disable paths.
This implementation follows ATT&CK framework techniques related to privilege escalation through kernel memory corruption (TA0004-Privilege Escalation) and system compromise (TA0003-Initial Access) by addressing fundamental synchronization flaws that could be exploited by malicious actors. The approach demonstrates proper kernel development practices for managing complex concurrent access patterns in hardware acceleration drivers, providing a robust solution that prevents the race condition while maintaining system stability and performance characteristics essential for enterprise-grade QAT implementations.