CVE-2021-47033 in Linux
Summary
by MITRE • 02/28/2024
In the Linux kernel, the following vulnerability has been resolved:
mt76: mt7615: fix tx skb dma unmap
The first pointer in the txp needs to be unmapped as well, otherwise it will leak DMA mapping entries
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Analysis
by VulDB Data Team • 12/13/2024
The vulnerability identified as CVE-2021-47033 affects the Linux kernel's mt76 wireless driver module, specifically targeting the mt7615 chipset implementation. This issue resides within the transmit packet handling mechanism where DMA (Direct Memory Access) mapping entries are improperly managed during wireless frame transmission. The flaw represents a memory management oversight that occurs when processing transmitted packets through the MediaTek mt7615 wireless network adapter driver. The vulnerability demonstrates a classic resource leak pattern where DMA mapping entries remain allocated in the system's memory management tables even after the corresponding network packets have been processed and transmitted.
The technical root cause of this vulnerability stems from an incomplete DMA unmap operation within the transmit packet processing pipeline. When network frames are prepared for transmission through the mt7615 driver, the system allocates DMA mapping entries to facilitate direct memory access between the wireless hardware and system memory. However, the implementation fails to properly unmap the first pointer in the txp (transmit packet) structure, causing these DMA mappings to persist indefinitely in the kernel's DMA mapping table. This creates a gradual accumulation of unmapped DMA entries that consume system resources and can eventually lead to resource exhaustion.
The operational impact of this vulnerability manifests as a progressive memory leak within the kernel's DMA mapping subsystem, potentially leading to system instability and performance degradation. As the DMA mapping entries accumulate over time, they consume valuable kernel memory resources that could otherwise be utilized for legitimate network operations. In extreme scenarios, this resource exhaustion could cause the wireless adapter to become unresponsive or trigger system-wide memory allocation failures that affect other kernel components. The vulnerability is particularly concerning in environments where continuous wireless data transmission occurs, as the leak rate increases proportionally with network activity levels.
From a cybersecurity perspective, this vulnerability aligns with CWE-404, which addresses improper resource management, specifically the failure to release resources properly. The issue also relates to ATT&CK technique T1059, where adversaries might exploit resource exhaustion vulnerabilities to cause system instability or denial of service conditions. The vulnerability demonstrates how seemingly minor memory management oversights in kernel drivers can create persistent security risks that may be exploited to degrade system performance or availability. Mitigation strategies should focus on updating the affected Linux kernel to versions containing the fix, which properly implements the DMA unmap operation for all pointers within the txp structure. System administrators should prioritize patching affected systems and monitoring for unusual memory consumption patterns that might indicate the presence of this vulnerability in unpatched environments.