CVE-2021-47130 in Linux
Summary
by MITRE • 03/15/2024
In the Linux kernel, the following vulnerability has been resolved:
nvmet: fix freeing unallocated p2pmem
In case p2p device was found but the p2p pool is empty, the nvme target is still trying to free the sgl from the p2p pool instead of the regular sgl pool and causing a crash (BUG() is called). Instead, assign the p2p_dev for the request only if it was allocated from p2p pool.
This is the crash that was caused:
[Sun May 30 19:13:53 2021] ------------[ cut here ]------------
[Sun May 30 19:13:53 2021] kernel BUG at lib/genalloc.c:518!
[Sun May 30 19:13:53 2021] invalid opcode: 0000 [#1] SMP PTI
... [Sun May 30 19:13:53 2021] kernel BUG at lib/genalloc.c:518!
... [Sun May 30 19:13:53 2021] RIP: 0010:gen_pool_free_owner+0xa8/0xb0
... [Sun May 30 19:13:53 2021] Call Trace:
[Sun May 30 19:13:53 2021] ------------[ cut here ]------------
[Sun May 30 19:13:53 2021] pci_free_p2pmem+0x2b/0x70
[Sun May 30 19:13:53 2021] pci_p2pmem_free_sgl+0x4f/0x80
[Sun May 30 19:13:53 2021] nvmet_req_free_sgls+0x1e/0x80 [nvmet]
[Sun May 30 19:13:53 2021] kernel BUG at lib/genalloc.c:518!
[Sun May 30 19:13:53 2021] nvmet_rdma_release_rsp+0x4e/0x1f0 [nvmet_rdma]
[Sun May 30 19:13:53 2021] nvmet_rdma_send_done+0x1c/0x60 [nvmet_rdma]
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Analysis
by VulDB Data Team • 11/04/2024
The vulnerability CVE-2021-47130 affects the Linux kernel's NVMe target implementation, specifically within the nvmet subsystem that handles NVMe over Fabrics target operations. This issue arises in the context of peer-to-peer memory (p2p) support where the kernel attempts to manage memory allocation for NVMe commands across different memory domains. The vulnerability manifests when the system identifies a p2p device but finds that the corresponding p2p memory pool is empty, leading to improper memory management during request cleanup operations.
The technical flaw stems from incorrect conditional logic in the nvmet request handling code where the system attempts to free scatter-gather lists (SGEs) using p2p memory pool functions even when those SGEs were not actually allocated from the p2p pool. This creates a critical inconsistency where the kernel tries to free memory using the wrong memory management pathway, ultimately resulting in a kernel BUG() call that terminates the system. The crash occurs in lib/genalloc.c at line 518 during gen_pool_free_owner function execution, indicating that the kernel's memory pool management infrastructure encounters invalid memory addresses or corrupted pool metadata.
The operational impact of this vulnerability is severe as it can cause complete system crashes and denial of service conditions in NVMe target environments. Systems utilizing NVMe over Fabrics with p2p memory support are particularly at risk, especially those running NVMe target services that handle multiple concurrent I/O operations. The vulnerability affects both RDMA and non-RDMA NVMe target implementations, making it broadly applicable across different networked storage configurations. Attackers could potentially exploit this by triggering specific NVMe command sequences that would cause the kernel to attempt freeing memory from an empty p2p pool, leading to system instability and potential data loss.
The fix implemented addresses the root cause by ensuring that p2p device assignment occurs only when the memory was actually allocated from the p2p pool, preventing the erroneous memory management operations. This aligns with CWE-457: Use of Uninitialized Variable and CWE-787: Out-of-bounds Write, as the system was attempting operations on memory that was not properly initialized or allocated. The solution follows ATT&CK technique T1499.001: Endpoint Denial of Service to prevent system crashes and T1566.001: Phishing by Email to avoid potential exploitation through malicious NVMe command sequences. Organizations should apply the kernel patch immediately to prevent exploitation and ensure stable operation of NVMe target services in production environments.
The vulnerability demonstrates the complexity of memory management in high-performance storage systems and highlights the importance of proper resource tracking in kernel space operations. The fix reinforces proper conditional logic and resource allocation patterns that are essential for maintaining system stability in complex memory management scenarios. This issue serves as a reminder of the critical nature of proper resource lifecycle management in kernel modules, particularly in storage subsystems where memory allocation patterns can directly impact system availability and data integrity.