CVE-2021-47048 in Linux
Summary
by MITRE • 02/28/2024
In the Linux kernel, the following vulnerability has been resolved:
spi: spi-zynqmp-gqspi: fix use-after-free in zynqmp_qspi_exec_op
When handling op->addr, it is using the buffer "tmpbuf" which has been freed. This will trigger a use-after-free KASAN warning. Let's use temporary variables to store op->addr.val and op->cmd.opcode to fix this issue.
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Analysis
by VulDB Data Team • 08/18/2025
The vulnerability identified as CVE-2021-47048 represents a critical use-after-free condition within the Linux kernel's SPI subsystem, specifically affecting the zynqmp-gqspi driver implementation. This flaw exists in the spi-zynqmp-gqspi module responsible for managing SPI operations on Xilinx Zynq UltraScale+ MPSoC devices, where the driver fails to properly manage memory references during command execution operations. The vulnerability manifests when processing address operations through the zynqmp_qspi_exec_op function, creating a scenario where memory that has already been freed is subsequently accessed, leading to potential system instability and security implications.
The technical root cause of this vulnerability stems from improper memory management within the driver's command execution flow. When the driver processes spi_op structures containing address information, it attempts to reference the op->addr.val field and op->cmd.opcode fields using a temporary buffer named tmpbuf. However, this tmpbuf buffer gets freed during the execution sequence before the referenced values are properly utilized, creating a classic use-after-free scenario. This memory access pattern violates fundamental safe programming practices and creates opportunities for malicious actors to exploit the kernel's memory management. The vulnerability directly maps to CWE-416, which defines use-after-free conditions as a critical memory safety issue, and aligns with ATT&CK technique T1068 which targets local privilege escalation through kernel vulnerabilities.
The operational impact of this vulnerability extends beyond simple memory corruption, as it creates potential attack vectors for privilege escalation and system compromise. When a malicious user or process triggers the affected code path, the use-after-free condition can result in kernel memory corruption that may be exploited to execute arbitrary code with kernel privileges. This represents a significant security risk for embedded systems and devices running Linux kernels with the affected zynqmp-gqspi driver, particularly those used in industrial control systems, networking equipment, and automotive applications where such devices are common. The vulnerability affects systems that utilize Xilinx Zynq UltraScale+ MPSoC platforms and any software that depends on the SPI communication interfaces managed by this driver.
Mitigation strategies for CVE-2021-47048 focus on immediate kernel updates and patches provided by the Linux kernel maintainers. System administrators should prioritize applying the official kernel patches that address the specific memory management issue in the zynqmp_qspi_exec_op function, ensuring that temporary variables are used to store op->addr.val and op->cmd.opcode values before any buffer deallocation occurs. Additionally, organizations should implement comprehensive monitoring for KASAN warnings and memory corruption indicators within their kernel environments. The fix implemented in the patch involves restructuring the code to store the required field values in temporary variables before the buffer cleanup operation, preventing the access to freed memory. This approach aligns with secure coding practices recommended by the Linux kernel security team and follows established guidelines for preventing use-after-free vulnerabilities in kernel space drivers. Organizations should also consider implementing runtime protections such as kernel address space layout randomization and stack canaries to provide additional defense-in-depth against potential exploitation attempts.