CVE-2024-26999

What it actually does

Flawed rx irq flood mitigation in the pmac_zilog serial driver triggers spinlock recursion in uart_port when pmz_receive_chars calls pr_err leading to pmz_console_write, resulting in kernel crashes or non-functional serial rx.

Why it matters to the business

Affected Linux systems using pmac_zilog hardware as serial console may suffer unexpected crashes or loss of serial access, causing operational disruption on embedded or legacy hardware deployments.

How an attack unfolds

The issue is triggered internally by irq flood conditions rather than direct attacker input; the removed mitigation code itself introduced the recursion, with no evidence of active exploitation by external threat actors.

How to fix it

Update the Linux kernel to a version containing commit 69a02273e288011b521ee7c1f3ab2c23fda633ce or later stable releases that remove the flawed mitigation code entirely.

How to confirm the fix worked

Verify the presence of commit 69a02273e288011b521ee7c1f3ab2c23fda633ce in the kernel source tree or confirm the error message "pmz: rx irq flood" no longer appears in serial console logs under load.

Typical attack path

1. Trigger high volume of rx interrupts on pmac_zilog port
2. Mitigation code path executes pr_err during already-held spinlock
3. Recursion detected causing BUG splat or port disablement

How to detect it

Search kernel logs and serial console output for strings indicating rx irq flood or spinlock recursion; correlate with pmac_zilog driver activity on systems using the affected serial hardware.

• ttyPZ0: pmz: rx irq flood !
• BUG: spinlock recursion on CPU
• pmz_receive_chars
• pmz_console_write

What your security team should do

• Apply the referenced kernel commit or newer stable branch immediately on systems using pmac_zilog hardware
• Monitor serial console logs for spinlock BUG reports or rx irq flood messages as interim detection
• Test serial console functionality after upgrade to confirm no regression in irq handling