CVE-2025-21820

MediumCVSS 5.5/10Last modified Jun 17, 2026

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.

Metrics

CVSS 3.1 5.5/10CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness enumeration

CWE-667

Affected software

VendorProductVersions
LinuxLinux>= 74ea66d4ca061a3cd4c0e924e51b60e924644852, < e22a97700901ba5e8bf8db68056a0d50f9440cae; >= 74ea66d4ca061a3cd4c0e924e51b60e924644852, < de5bd24197bd9ee37ec1e379a3d882bbd15c5065; >= 74ea66d4ca061a3cd4c0e924e51b60e924644852, < 8ea0e7b3d7b8f2f0fc9db491ff22a0abe120801c; >= 74ea66d4ca061a3cd4c0e924e51b60e924644852, < 9b88a7c4584ba67267a051069b8abe44fc9595b2; >= 74ea66d4ca061a3cd4c0e924e51b60e924644852, < 4410dba9807a17a93f649a9f5870ceaf30a675a3; >= 74ea66d4ca061a3cd4c0e924e51b60e924644852, < b06f388994500297bb91be60ffaf6825ecfd2afe
LinuxLinux4.6

References

Timeline

Published
Feb 27, 2025
Last modified
Jun 17, 2026
NVD status
Modified

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CVE-2025-21820: Medium severity, CVSS 5.5 | Vulnix