CVE-2025-21820: tty: xilinx_uartps: split sysrq handling

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: 2025-02-27 · updated 2026-06-17
Weakness: CWE-667

Description

In the Linux kernel, the following vulnerability has been resolved: tty: xilinx_uartps: split sysrq handling lockdep detects the following circular locking dependency: CPU 0 CPU 1 ========================== ============================ cdns_uart_isr() printk() uart_port_lock(port) console_lock() cdns_uart_console_write() if (!port->sysrq) uart_port_lock(port) uart_handle_break() port->sysrq = ... uart_handle_sysrq_char() printk() console_lock() The fixed commit attempts to avoid this situation by only taking the port lock in cdns_uart_console_write if port->sysrq unset. However, if (as shown above) cdns_uart_console_write runs before port->sysrq is set, then it will try to take the port lock anyway. This may result in a deadlock. Fix this by splitting sysrq handling into two parts. We use the prepare helper under the port lock and defer handling until we release the lock.

Affected products

Linux kernel: from 4.6 before 6.1.129; from 6.2 before 6.6.78; from 6.7 before 6.12.14; from 6.13 before 6.13.3 — fixed in 6.1.129, 6.12.14, 6.13.3, 6.6.78

How to fix

Upgrade to a fixed version: Linux kernel 6.1.129, 6.12.14, 6.13.3, 6.6.78. Check the vendor advisory for mitigations.

References

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