CVE-2024-26999: serial/pmac_zilog: Remove flawed mitigation for rx irq flood

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-05-01 · updated 2026-06-17
Weakness: CWE-667

Description

In the Linux kernel, the following vulnerability has been resolved: serial/pmac_zilog: Remove flawed mitigation for rx irq flood The mitigation was intended to stop the irq completely. That may be better than a hard lock-up but it turns out that you get a crash anyway if you're using pmac_zilog as a serial console: ttyPZ0: pmz: rx irq flood ! BUG: spinlock recursion on CPU#0, swapper/0 That's because the pr_err() call in pmz_receive_chars() results in pmz_console_write() attempting to lock a spinlock already locked in pmz_interrupt(). With CONFIG_DEBUG_SPINLOCK=y, this produces a fatal BUG splat. The spinlock in question is the one in struct uart_port. Even when it's not fatal, the serial port rx function ceases to work. Also, the iteration limit doesn't play nicely with QEMU, as can be seen in the bug report linked below. A web search for other reports of the error message "pmz: rx irq flood" didn't produce anything. So I don't think this code is needed any more. Remove it.

Affected products

Debian Linux: 10.0
Linux kernel: from 2.6.12 before 5.15.157; from 5.16 before 6.1.88; from 6.2 before 6.6.29; from 6.7 before 6.8.8; 6.9-rc1, 6.9-rc2, 6.9-rc3, 6.9-rc4 — fixed in 5.15.157, 6.1.88, 6.6.29, 6.8.8

How to fix

Upgrade to a fixed version: Linux kernel 5.15.157, 6.1.88, 6.6.29, 6.8.8. Check the vendor advisory for mitigations.

References

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