CVE-2021-47071 in Linux
Summary
by MITRE • 03/02/2024
In the Linux kernel, the following vulnerability has been resolved:
uio_hv_generic: Fix a memory leak in error handling paths
If 'vmbus_establish_gpadl()' fails, the (recv|send)_gpadl will not be updated and 'hv_uio_cleanup()' in the error handling path will not be able to free the corresponding buffer.
In such a case, we need to free the buffer explicitly.
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Analysis
by VulDB Data Team • 06/20/2025
The vulnerability CVE-2021-47071 represents a memory leak in the Linux kernel's hypervisor communication subsystem, specifically within the uio_hv_generic driver that facilitates user-space I/O operations for Hyper-V virtual machines. This flaw exists in the error handling pathways of the virtual machine bus (vmbus) implementation, which serves as the communication interface between the host and guest operating systems in virtualized environments. The vulnerability occurs when the vmbus_establish_gpadl() function fails during the establishment of generalized pass-through direct memory access (GPADL) connections, which are essential for efficient memory sharing between virtual machines and their hosts. The issue stems from improper resource management where the system fails to clean up allocated memory buffers when error conditions occur during the GPADL establishment process.
The technical flaw manifests when the vmbus_establish_gpadl() function returns an error status, indicating that the GPADL connection could not be properly established between the virtual machine and the host hypervisor. Under normal circumstances, the system would update the receive and send GPADL handles to reference the newly established connections. However, in error scenarios, these handles remain unupdated while the cleanup routine hv_uio_cleanup() attempts to free memory resources. This inconsistency creates a memory leak because the cleanup function cannot properly identify and release the allocated buffer space, leaving memory fragments that cannot be reclaimed by the system. The vulnerability specifically affects the uio_hv_generic driver's handling of error conditions, where the system's resource management logic fails to account for the possibility that GPADL establishment may fail after memory allocation has occurred. This memory leak represents a classic resource management issue that can lead to gradual system degradation over time.
The operational impact of this vulnerability extends beyond simple memory consumption, particularly in virtualized environments where multiple VMs may experience similar resource exhaustion. When the memory leak occurs repeatedly across different virtual machine instances or during high-frequency communication scenarios, it can result in progressive memory pressure that affects overall system performance and stability. The vulnerability is particularly concerning in cloud computing and containerized environments where virtual machines operate under strict resource constraints, as the memory leak could eventually lead to system crashes or performance degradation that impacts service availability. Attackers who can trigger this error condition repeatedly may be able to cause denial-of-service scenarios by exhausting available memory resources, making this vulnerability particularly dangerous in production environments. The issue also represents a failure in the kernel's resource management patterns, specifically in how error handling paths interact with memory allocation and deallocation routines.
Mitigation strategies for CVE-2021-47071 focus on ensuring proper error handling and resource cleanup in the kernel's virtual machine bus implementation. System administrators should prioritize applying the relevant kernel patches that implement explicit buffer cleanup in error paths, which addresses the root cause by ensuring that allocated memory is freed regardless of whether the GPADL establishment succeeds or fails. The fix typically involves modifying the error handling logic to explicitly free the allocated buffers before returning error codes, thereby preventing the memory leak condition. Organizations should also implement monitoring systems to detect memory usage patterns that might indicate the presence of similar resource management issues, particularly in virtualized environments where such vulnerabilities are more likely to manifest. The vulnerability aligns with CWE-401, which specifically addresses memory leaks in software systems, and represents a failure in proper resource management practices. From an ATT&CK framework perspective, this vulnerability could be leveraged as part of a resource exhaustion attack, potentially enabling adversaries to cause system instability or perform denial-of-service operations against virtualized infrastructure. Regular kernel updates and security audits of virtualization components remain essential practices for preventing exploitation of such memory management vulnerabilities.