CVE-2021-47367 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
virtio-net: fix pages leaking when building skb in big mode
We try to use build_skb() if we had sufficient tailroom. But we forget to release the unused pages chained via private in big mode which will leak pages. Fixing this by release the pages after building the skb in big mode.
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Analysis
by VulDB Data Team • 05/21/2024
The vulnerability identified as CVE-2021-47367 represents a memory management flaw within the Linux kernel's virtio-net driver implementation. This issue specifically affects systems utilizing virtualized network interfaces where the kernel attempts to optimize memory allocation by using the build_skb() function when sufficient tailroom is available. The flaw occurs in what is known as "big mode" operation, where the kernel's network stack processes packets with larger memory requirements. The vulnerability stems from an incomplete memory cleanup process that fails to properly release unused memory pages that are chained through the private data structure when building socket buffer objects.
The technical root cause of this vulnerability lies in the improper handling of memory pages during the packet processing lifecycle within the virtio-net subsystem. When the kernel's network driver operates in big mode, it allocates memory pages to accommodate larger packet sizes and chains these pages through the private data structure of the socket buffer. However, the implementation fails to release these unused pages after the socket buffer construction is complete, resulting in a memory leak that accumulates over time. This memory leak directly violates the principle of proper resource management and can lead to progressive system degradation. The flaw is classified under CWE-401 as a weakness related to improper release of memory after transfer of ownership, and it aligns with ATT&CK technique T1490 which covers resource exhaustion through memory leaks.
The operational impact of this vulnerability extends beyond simple memory consumption issues, potentially leading to system instability and performance degradation in virtualized environments. As memory pages leak continuously, the available system memory decreases progressively, which can trigger memory pressure conditions and affect overall system responsiveness. In high-throughput virtualized environments where virtio-net interfaces are heavily utilized, this memory leak can accumulate rapidly and may eventually contribute to system crashes or forced reboots. The vulnerability particularly affects cloud computing environments and virtual machine deployments where multiple network interfaces are active simultaneously, making it a significant concern for infrastructure providers and enterprise users.
Mitigation strategies for CVE-2021-47367 primarily involve applying the kernel patch that properly releases the unused memory pages after socket buffer construction in big mode. System administrators should prioritize updating their Linux kernel versions to include the fix, which is typically available in kernel versions 5.13 and later. Organizations should also implement monitoring solutions to track memory usage patterns and detect potential memory leaks before they cause system instability. Additionally, regular system maintenance procedures should include kernel updates and security patches to prevent exploitation of similar vulnerabilities. The fix addresses the root cause by ensuring proper memory cleanup through explicit page release operations after the build_skb() function completes its execution, thereby maintaining the integrity of the kernel's memory management subsystem and preventing unauthorized resource consumption that could be exploited by malicious actors.