CVE-2020-12769 in Linux
Summary
by MITRE
An issue was discovered in the Linux kernel before 5.4.17. drivers/spi/spi-dw.c allows attackers to cause a panic via concurrent calls to dw_spi_irq and dw_spi_transfer_one, aka CID-19b61392c5a8.
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Analysis
by VulDB Data Team • 10/16/2020
The vulnerability identified as CVE-2020-12769 represents a critical concurrency issue within the Linux kernel's DesignWare SPI driver implementation. This flaw exists in the spi-dw.c file and affects kernel versions prior to 5.4.17, creating a potential system panic condition that can be triggered by malicious actors. The vulnerability stems from improper synchronization mechanisms within the driver's interrupt handling and transfer functions, specifically when these two functions are invoked simultaneously from different execution contexts.
The technical root cause of this vulnerability lies in the lack of proper mutual exclusion controls between the dw_spi_irq interrupt handler and the dw_spi_transfer_one transfer function. When these two functions execute concurrently, they can access and modify shared data structures without adequate locking mechanisms, leading to race conditions that corrupt kernel memory state. This particular issue falls under the CWE-362 category of Concurrent Execution using Shared Resource with Unprotected Shared Data, which is a well-documented pattern of vulnerabilities in kernel space programming where multiple execution paths access common resources without proper synchronization. The race condition manifests when the interrupt handler attempts to process SPI transaction completions while the transfer function is simultaneously managing new transactions, creating a scenario where kernel data structures become corrupted.
The operational impact of this vulnerability is severe as it can lead to complete system crashes or panics, effectively causing a denial of service condition that renders the affected system unusable. Attackers can exploit this weakness by crafting specific sequences of SPI operations that force the kernel to execute both functions concurrently, triggering the race condition and resulting in a kernel panic. This vulnerability is particularly concerning because it operates at the kernel level where such failures can compromise the entire system stability. The attack surface is broad as any system utilizing DesignWare SPI controllers and executing concurrent SPI operations could be affected, making this a significant concern for embedded systems, servers, and devices that rely on SPI communication protocols for various hardware interactions.
Mitigation strategies for CVE-2020-12769 involve immediate kernel version updates to 5.4.17 or later where the fix has been implemented. The patch addresses the issue by introducing proper locking mechanisms between the interrupt handler and transfer functions, ensuring that shared resources are accessed exclusively. Organizations should also consider implementing runtime checks to monitor for concurrent SPI operations and potentially disable problematic SPI configurations until proper updates are deployed. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving privilege escalation and denial of service, as it allows attackers to potentially gain system control through kernel-level exploitation. System administrators should also monitor for unusual system panics or crashes that could indicate exploitation attempts, and maintain comprehensive backup and recovery procedures to address potential system instability caused by this vulnerability.