CVE-2024-26786 in Linux
Summary
by MITRE • 04/04/2024
In the Linux kernel, the following vulnerability has been resolved:
iommufd: Fix iopt_access_list_id overwrite bug
Syzkaller reported the following WARN_ON: WARNING: CPU: 1 PID: 4738 at drivers/iommu/iommufd/io_pagetable.c:1360
Call Trace: iommufd_access_change_ioas+0x2fe/0x4e0 iommufd_access_destroy_object+0x50/0xb0 iommufd_object_remove+0x2a3/0x490 iommufd_object_destroy_user iommufd_access_destroy+0x71/0xb0 iommufd_test_staccess_release+0x89/0xd0 __fput+0x272/0xb50 __fput_sync+0x4b/0x60 __do_sys_close __se_sys_close __x64_sys_close+0x8b/0x110 do_syscall_x64
The mismatch between the access pointer in the list and the passed-in pointer is resulting from an overwrite of access->iopt_access_list_id, in iopt_add_access(). Called from iommufd_access_change_ioas() when xa_alloc() succeeds but iopt_calculate_iova_alignment() fails.
Add a new_id in iopt_add_access() and only update iopt_access_list_id when returning successfully.
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Analysis
by VulDB Data Team • 08/04/2025
The vulnerability CVE-2024-26786 affects the Linux kernel's iommufd subsystem, specifically within the iommu framework's device memory access management functionality. This issue manifests as a critical data corruption bug that occurs during the management of IOMMU access lists, where the iopt_access_list_id field becomes overwritten during the access list management process. The vulnerability was identified through systematic kernel testing using syzkaller, a powerful fuzzer that has historically uncovered numerous kernel-level security issues. The warning trace indicates the problem originates from a critical path involving iommufd_access_change_ioas function which handles access list modifications. The call stack shows the execution flow leading to the kernel's internal warning mechanism, demonstrating how the bug propagates through multiple layers of the iommufd subsystem before triggering the WARN_ON condition. This represents a fundamental flaw in the kernel's memory management and object reference handling within the IOMMU subsystem.
The technical root cause of this vulnerability lies in the improper handling of the iopt_access_list_id field during the iopt_add_access() function execution. When xa_alloc() successfully allocates memory for a new access entry but iopt_calculate_iova_alignment() subsequently fails, the system enters an inconsistent state where the access pointer in the list becomes mismatched with the pointer being passed in. This mismatch occurs because the iopt_access_list_id field gets overwritten without proper validation, creating a scenario where the kernel maintains incorrect references to access objects. The vulnerability specifically targets the synchronization mechanism between the access list management and the actual memory allocation process, where error handling fails to properly rollback state changes. This type of bug falls under CWE-129 Input Validation and the broader category of improper handling of memory references, directly impacting the kernel's memory safety guarantees.
The operational impact of this vulnerability is significant as it can lead to kernel crashes, memory corruption, and potential privilege escalation scenarios within the IOMMU subsystem. When the iopt_access_list_id field becomes corrupted, it can cause the kernel to reference invalid memory locations or manipulate objects in unintended ways, potentially leading to system instability or denial of service conditions. The vulnerability affects systems that utilize IOMMU virtualization features, particularly those implementing iommufd for device memory access management. Attackers could potentially exploit this condition to cause system panics, leading to service disruption, or in more sophisticated scenarios, leverage the memory corruption for privilege escalation attacks. The vulnerability is particularly concerning in virtualized environments where IOMMU functionality is heavily utilized for device passthrough and memory isolation.
Mitigation strategies for this vulnerability should focus on immediate kernel updates to address the specific bug in iopt_add_access() function. The fix involves introducing a new_id variable in the iopt_add_access() function and only updating the iopt_access_list_id field when the function returns successfully, thereby preventing premature overwrites during error conditions. System administrators should prioritize applying the latest kernel patches that contain this fix, particularly for systems running Linux kernel versions that include the affected iommufd subsystem. Additional monitoring should be implemented to detect kernel warnings related to IOMMU access management, as these may indicate exploitation attempts or system instability. Organizations should also consider implementing runtime protections such as kernel lockdown modes and ensuring proper access controls are in place for IOMMU-related operations. The fix aligns with ATT&CK technique T1068, which involves exploiting local privilege escalation opportunities, and addresses the underlying memory management weaknesses that enable such attacks. Regular kernel security auditing and continuous monitoring of kernel subsystems for similar race condition vulnerabilities should be implemented as part of comprehensive security hardening practices.