CVE-2026-46225: Linux RSPI Driver Denial of Service via Improper Resource Deregistration

Technical summary

CVE-2026-46225 addresses a resource management issue in the Linux kernel's SPI RSPI driver (drivers/spi/spi-rspi.c). The vulnerability stems from improper sequencing during driver unbind: the driver was releasing DMA resources before deregistering the SPI controller. This violates the correct tear-down sequence and can lead to use-after-free or NULL pointer dereference conditions when the controller attempts to access DMA handles or operations after they have been freed. The fix ensures the controller is deregistered first, allowing it to complete any pending operations and cleanly disconnect from the SPI framework before underlying DMA resources are released.

Business impact

Systems running affected Linux kernel versions that use RSPI controllers face potential availability risk. Driver unload or system shutdown scenarios could trigger kernel panics or hangs, disrupting service availability. In environments relying on SPI-based hardware devices (industrial controllers, embedded systems, specialized automotive or IoT deployments), this flaw increases downtime risk during maintenance windows or unexpected unload scenarios. The impact is primarily operational stability rather than data confidentiality or integrity.

Affected systems

The vulnerability affects the Linux kernel across all versions that contain the vulnerable RSPI driver code. Any system using an RSPI-compatible SPI controller—including certain Renesas microcontroller platforms and boards with RSPI hardware—running an unpatched kernel is at risk during driver unbind or module removal operations.

Exploitability

This vulnerability requires local access to trigger (CVSS attack vector: Local). An unprivileged local user with the ability to unload kernel modules or trigger driver unbind operations can cause a denial of service. The flaw is not remotely exploitable and does not enable privilege escalation or data theft. Exploitation is straightforward once local access is available, as it occurs during normal driver lifecycle operations.

Remediation

Apply a kernel update that includes the fix to ensure proper controller deregistration sequencing. The patch reorders the cleanup logic so that spi_unregister_controller() is called before DMA resources are released. Verify the specific kernel version or patch against the Linux kernel repository and your distribution's advisory. Systems should schedule maintenance windows to apply the patched kernel and reboot.

Patch guidance

Monitor your Linux distribution's security advisories for kernel updates that address this issue. Once available, install the patched kernel version and reboot the system to activate the fix. If you maintain custom kernels, pull the upstream fix from the Linux kernel repository and rebuild. Verify the patch commit references proper deregistration sequencing before DMA cleanup. Test driver unload/rebind operations in a non-production environment first if feasible.

Detection guidance

Monitor kernel logs (dmesg, journalctl) for SPI controller or DMA-related warnings, NULL pointer dereference messages, or kernel panics occurring during driver unload or module removal. If you see stack traces involving spi-rspi.c or DMA teardown routines, investigate whether you are running a vulnerable kernel version. Check your kernel version with `uname -r` and cross-reference against vendor advisories. Systems using RSPI hardware should be inventoried and prioritized for patching.

Why prioritize this

Although marked MEDIUM severity (CVSS 5.5), this vulnerability should be prioritized for patching in environments where RSPI hardware is active or where frequent driver management occurs. The local-only and high-availability impact make it lower priority than remote exploitable flaws, but the straightforward trigger mechanism during normal operations (driver unload) elevates practical risk. Systems with SPI-dependent hardware or those performing regular kernel module management should patch sooner; general-purpose servers with no RSPI hardware can defer slightly longer but should not ignore the fix.

Risk score, explained

CVSS 3.1 score of 5.5 (MEDIUM) reflects: local attack vector (cannot be exploited remotely), low attack complexity (normal driver operations), low privileges required (unprivileged user can unload modules), no user interaction needed, single user scope, and high availability impact (denial of service via crash). The score appropriately captures that while impact is real and easy to trigger locally, the restriction to local access and lack of confidentiality/integrity compromise limit the overall severity. The real-world risk depends on your reliance on RSPI hardware and frequency of driver lifecycle operations.

Frequently asked questions