CVE-2021-47177 in Linux
Summary
by MITRE • 03/25/2024
In the Linux kernel, the following vulnerability has been resolved:
iommu/vt-d: Fix sysfs leak in alloc_iommu()
iommu_device_sysfs_add() is called before, so is has to be cleaned on subsequent errors.
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Analysis
by VulDB Data Team • 11/23/2025
The vulnerability identified as CVE-2021-47177 represents a critical resource management flaw within the Linux kernel's IOMMU (Input-Output Memory Management Unit) subsystem, specifically affecting the Intel Virtualization Technology for Directed I/O (VT-d) implementation. This issue manifests as a sysfs leak occurring during the allocation process of IOMMU devices, where the kernel fails to properly clean up previously initialized sysfs entries when subsequent errors occur during device allocation. The problem stems from the improper handling of system filesystem entries within the kernel's device management framework, creating a potential avenue for resource exhaustion and system instability.
The technical root cause of this vulnerability lies in the improper error handling sequence within the alloc_iommu() function, which is responsible for allocating IOMMU device resources in virtualized environments. When iommu_device_sysfs_add() is invoked to register a device within the sysfs filesystem, it creates the necessary filesystem entries to expose device information to user space. However, if subsequent operations within the allocation process fail, the cleanup mechanism fails to properly remove these sysfs entries, resulting in leaked filesystem objects that persist in memory and can accumulate over time. This represents a classic resource leak pattern that can degrade system performance and potentially lead to denial of service conditions. The vulnerability directly maps to CWE-404, which describes improper resource release or recovery, and aligns with ATT&CK technique T1490, specifically targeting resource exhaustion through improper resource management.
The operational impact of CVE-2021-47177 extends beyond simple memory consumption, as it can significantly affect virtualized environments where IOMMU functionality is heavily utilized. Systems running virtual machines, containerized applications, or any workload requiring hardware virtualization through VT-d are particularly vulnerable to this flaw. The leak can occur repeatedly during device allocation failures, potentially leading to system instability, reduced performance, or complete system hangs when system resources become exhausted. In cloud computing environments or server deployments where IOMMU allocation occurs frequently, this vulnerability can compound over time, creating a persistent degradation in system reliability and potentially enabling attackers to perform resource exhaustion attacks against virtualized workloads. The vulnerability affects kernel versions prior to the fix, particularly impacting enterprise systems running virtualization platforms that rely on Intel VT-d technology for hardware isolation and security.
Mitigation strategies for CVE-2021-47177 focus on implementing proper error handling and resource cleanup mechanisms within the kernel's IOMMU subsystem. The primary fix involves ensuring that iommu_device_sysfs_remove() is called whenever iommu_device_sysfs_add() has been invoked, regardless of subsequent allocation success or failure conditions. System administrators should prioritize kernel updates to versions containing the patched implementation, which typically includes the specific fix for the alloc_iommu() function. Organizations running virtualized environments should implement monitoring for resource consumption patterns and establish alerting mechanisms for unusual sysfs entry accumulation. Additionally, security teams should consider implementing runtime protections that can detect and prevent repeated allocation failures that may indicate exploitation attempts. The fix aligns with security best practices outlined in the Linux kernel security documentation and represents a standard defensive programming approach to ensure proper resource management and error recovery in kernel space operations.