CVE-2021-47070 in Linux
Summary
by MITRE • 03/02/2024
In the Linux kernel, the following vulnerability has been resolved:
uio_hv_generic: Fix another memory leak in error handling paths
Memory allocated by 'vmbus_alloc_ring()' at the beginning of the probe function is never freed in the error handling path.
Add the missing 'vmbus_free_ring()' call.
Note that it is already freed in the .remove function.
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Analysis
by VulDB Data Team • 11/23/2025
The vulnerability identified as CVE-2021-47070 represents a memory leak condition within the Linux kernel's Hyper-V user input/output (UIO) subsystem, specifically affecting the uio_hv_generic driver component. This issue manifests in the context of virtualization environments where Hyper-V guests communicate with host systems through the vmbus interface. The flaw occurs during the device probe phase when memory allocation operations are performed but not properly cleaned up under error conditions. The vulnerability directly impacts the stability and resource management capabilities of virtualized systems, particularly those relying on Hyper-V integration services for device communication.
The technical root cause of this memory leak stems from improper error handling within the uio_hv_generic driver's probe function implementation. When the vmbus_alloc_ring() function successfully allocates memory for the Hyper-V ring buffer structure, this allocated memory resource is not released during error pathways that occur before the normal device initialization completes. The memory allocation occurs at the beginning of the probe function execution, but the corresponding cleanup mechanism through vmbus_free_ring() is omitted in the error handling code paths. This creates a situation where allocated kernel memory remains in use indefinitely, leading to progressive memory consumption that can eventually impact system performance and stability.
The operational impact of this vulnerability extends beyond simple memory consumption issues, as it represents a classic resource management flaw that can be exploited to cause denial of service conditions in virtualized environments. Systems running multiple virtual machines or heavily utilizing Hyper-V integration services may experience progressive memory degradation, potentially leading to system instability or complete resource exhaustion. The vulnerability affects any Linux kernel version that includes the uio_hv_generic driver component and is particularly concerning in production environments where virtualization resources are heavily utilized. The memory leak compounds over time, making it difficult to detect and diagnose as a gradual performance degradation rather than an immediate system failure.
The fix for CVE-2021-47070 involves adding the missing vmbus_free_ring() function call within the error handling paths of the uio_hv_generic driver's probe function. This remediation ensures that all memory allocated by vmbus_alloc_ring() is properly released regardless of whether the device initialization succeeds or fails. The solution follows established kernel programming practices for resource management and aligns with the principle of defensive programming where all allocated resources must be freed in all code paths. This vulnerability demonstrates the importance of proper error handling in kernel modules and highlights the critical nature of memory management in virtualization contexts. The fix also reinforces the principle that resource cleanup should occur in the same function where resources are allocated, following the common pattern of allocation followed by deallocation in error handling scenarios. The issue relates to CWE-404, which addresses improper resource release or cleanup, and aligns with ATT&CK technique T1490, which covers resource hijacking through memory exhaustion attacks.