CVE-2026-89795
HighCVSS 8.4Summary
A vulnerability in the Linux kernel PCI subsystem affecting s390 systems using a machine-level hypervisor has been resolved. The shared pci_slot assignment for multifunction devices caused the hotplug driver to reset the wrong function and leak memory. A flag was added to allow per-function PCI slots for hypervisor-managed functions.
Risk Assessment
On s390 systems with multifunction PCI devices, a hotplug reset may target the wrong function, causing unpredictable device failures and a kernel memory leak. This can lead to system instability and require a reboot.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-89795. If s390 systems are not in use, the risk is negligible, but the update should still be included in the regular patching cycle.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: PCI: Allow per function PCI slots to fix slot reset on s390 On s390 systems, which use a machine level hypervisor, PCI devices are always accessed through a form of PCI pass-through which fundamentally operates on a per PCI function granularity. This is also reflected in the s390 PCI hotplug driver which creates hotplug slots for individual PCI functions. Its reset_slot() function, which is a wrapper for zpci_hot_reset_device(), thus also resets individual functions. Currently, the pci_create_slot() assigns the same pci_slot object to multifunction devices. This approach worked fine on s390 systems that only exposed virtual functions as individual PCI domains to the operating system. Since commit 44510d6fa0c0 ("s390/pci: Handling multifunctions") s390 supports exposing the topology of multifunction PCI devices by grouping them in a shared PCI domain. This creates a problem when resetting a function through the hotplug driver's slot_reset() interface. When attempting to reset a function through the hotplug driver, the shared slot assignment causes the wrong function to be reset instead of the intended one. It also leaks memory as we do create a pci_slot object for the function, but don't correctly free it in pci_slot_release(). Add a flag for struct pci_slot to allow per function PCI slots for functions managed through a hypervisor, which exposes individual PCI functions while retaining the topology. Since we can use all 8 bits for slot 'number' (for ARI devices), change slot 'number' u16 to account for special values PCI_SLOT_PLACEHOLDER and PCI_SLOT_ALL_DEVICES.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS