CVE-2024-26999 serial/pmac_zilog: Remove flawed mitigation for rx irq flood
A flawed mitigation in the Linux kernel's pmac_zilog serial driver causes a crash or denial of service when handling RX IRQ floods, particularly with debug spinlocks enabled.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-26999?
CVE-2024-26999 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 1 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-667
Which versions are affected by CVE-2024-26999?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2024-26999?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2024-26999 being exploited?
There is no known exploitation of CVE-2024-26999 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as BELL-CVE-2024-26999, DEBIAN-CVE-2024-26999, GHSA-hwgv-6mjr-cw48, UBUNTU-CVE-2024-26999.