CVE-2024-26977

What it actually does

A misplaced #ifdef ARCH_HAS_GENERIC_IOPORT_MAP guard in pci_iounmap() skips the iounmap() call for MMIO mappings, causing kernel memory mapping leaks.

Why it matters to the business

Long-running Linux systems performing repeated PCI device mapping operations may experience gradual kernel memory exhaustion, increasing the risk of instability or crashes during extended uptime.

How an attack unfolds

An attacker triggers repeated PCI device attach/detach or mapping operations that invoke the vulnerable pci_iounmap path; each missed unmap accumulates leaked kernel mappings until resource pressure leads to denial of service or facilitates further memory corruption attacks.

How to fix it

Upgrade the Linux kernel to a version containing commit 5e4b23e7a7b33a1e56bfa3e5598138a2234d55b6 or later; rebuild and deploy the updated kernel across all affected systems.

How to confirm the fix worked

Inspect the pci_iounmap() implementation to confirm the iounmap() call is no longer guarded by ARCH_HAS_GENERIC_IOPORT_MAP; run regression tests exercising PCI MMIO map/unmap paths and monitor for mapping leaks.

Typical attack path

1. Locate or create a user-space or driver context that exercises pci_iounmap() on MMIO regions
2. Repeatedly trigger mapping and attempted unmapping cycles
3. Accumulate leaked mappings until kernel memory pressure manifests
4. Leverage resulting instability or adjacent memory corruption for privilege escalation

How to detect it

Review kernel logs and dmesg output for repeated allocation warnings or OOM killer activity tied to PCI or MMIO operations; examine source trees for the original misplaced preprocessor guard around iounmap().

What your security team should do

• Prioritize kernel upgrades on all production Linux hosts within the next maintenance window
• Audit custom or third-party PCI drivers for direct calls to the affected mapping functions
• Enable kernel memory leak detectors and monitor for anomalous allocation growth
• Subscribe to stable kernel update channels to receive future fixes promptly