CVE-2025-21820

/// Technical 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 w

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References