CVE-2026-64462: Linux Kernel Privilege Escalation Flaw

CVE-2026-64462 Overview

CVE-2026-64462 is a Linux kernel vulnerability in the Altera PCI Express (PCIe) host controller driver. The flaw involves resource leaks and a stale pointer condition triggered when pci_host_probe() fails during driver initialization. The chained interrupt request (IRQ) handler is registered during probe but only unregistered during driver remove(). If probe fails, the devm-managed host bridge storage containing the altera_pcie structure is released while the handler retains a reference to that memory, leaving a stale data pointer.

Critical Impact
A failed probe of the Altera PCIe controller leaves a chained IRQ handler pointing to freed memory, which can trigger use-after-free conditions when interrupts fire.

Affected Products

Linux kernel builds including the Altera PCIe host controller driver (pcie-altera)
Stable kernel branches referenced by fix commits 09c43b7, 0db9aa9, 6864c78, 7a94138, 99fc088, 9cf0cc4, a25bfa2, af7cf5d
Systems using Altera/Intel FPGA PCIe root complex configurations

Discovery Timeline

2026-07-25 - CVE-2026-64462 published to the National Vulnerability Database (NVD)
2026-07-25 - Last updated in NVD database

Technical Details for CVE-2026-64462

Vulnerability Analysis

The Altera PCIe host controller driver installs a chained IRQ handler during its probe() routine. The handler dispatches PCIe INTx legacy interrupts to child devices through an IRQ domain. The driver only tears down this handler in its remove() callback, assuming probe either succeeds fully or fails cleanly before installation.

The assumption breaks when pci_host_probe() fails. The struct altera_pcie is allocated using device-managed (devm) memory tied to the host bridge. When probe returns an error, the kernel releases the devm-managed allocations, but the chained handler installed earlier is never torn down. The handler retains a pointer to the now-freed altera_pcie structure.

Compounding this, the driver enables controller interrupts before calling pci_host_probe(). Any interrupt fired after probe failure but before full cleanup dereferences the stale pointer, producing a use-after-free [CWE-416] and potential memory corruption in kernel context.

Root Cause

The root cause is incorrect ordering of resource acquisition and error-path cleanup in the Altera PCIe driver probe() function. The chained IRQ handler and INTx IRQ domain are installed before pci_host_probe() runs, but the driver lacks corresponding rollback logic if pci_host_probe() returns an error. Device-managed memory is released automatically, while manually installed IRQ infrastructure is not.

Attack Vector

This is a local kernel reliability defect requiring probe-time failure of the Altera PCIe controller. Triggering the condition depends on hardware presence, PCIe enumeration errors, resource conflicts, or induced probe failures on affected FPGA-based platforms. An unprivileged remote attacker cannot reach the vulnerable code path directly. Exploitation as a memory-safety issue requires the ability to influence probe outcomes and interrupt delivery on the affected platform.

The upstream patch reorders operations so the chained handler is installed only after the INTx domain is created, disables controller interrupts during IRQ teardown, and adds explicit teardown when pci_host_probe() fails. See the Kernel Git Commit a25bfa2 for the fix.

Detection Methods for CVE-2026-64462

Indicators of Compromise

Kernel oops or panic messages referencing altera_pcie or the pcie-altera driver during boot or module load
Interrupt handler backtraces in dmesg pointing to freed memory addresses following a failed PCIe probe
Repeated PCIe host bridge probe failures on Altera or Intel FPGA hardware

Detection Strategies

Inventory running kernels against the fix commits and flag hosts using pcie-altera on unpatched builds
Parse dmesg and journalctl -k for altera PCIe probe failure sequences followed by IRQ warnings
Correlate kernel crash dumps with the affected driver path drivers/pci/controller/pcie-altera.c

Monitoring Recommendations

Forward kernel logs from FPGA-equipped systems to a centralized logging pipeline for probe-failure detection
Alert on unexpected kernel taints, WARN_ON events, or use-after-free reports from KASAN-instrumented kernels
Track host bridge enumeration status across fleet inventory to identify systems repeatedly failing PCIe probe

How to Mitigate CVE-2026-64462

Immediate Actions Required

Apply the upstream Linux kernel patches referenced in the stable tree commits for CVE-2026-64462
Rebuild and deploy kernels for systems using the Altera PCIe host controller driver
Restrict physical and administrative access to affected FPGA platforms until patched kernels are deployed

Patch Information

The fix was backported across multiple stable kernel branches. Reference commits: 09c43b7, 0db9aa9, 6864c78, 7a94138, 99fc088, 9cf0cc4, a25bfa2, and af7cf5d. The patches reorder handler installation, add interrupt disablement during teardown, and add error-path cleanup for pci_host_probe() failure.

Workarounds

Blacklist the pcie-altera module on systems that do not require Altera PCIe root complex functionality
Ensure PCIe hardware and firmware are healthy to reduce the probability of probe failures triggering the defect
Avoid repeated bind/unbind cycles of the driver on production systems until the patched kernel is installed

bash

# Blacklist the vulnerable driver on systems that do not need it
echo "blacklist pcie-altera" | sudo tee /etc/modprobe.d/blacklist-pcie-altera.conf
sudo update-initramfs -u