linux-cve-announce - CVE-2025-21820: tty: xilinx

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Message-ID: <2025022710-CVE-2025-21820-f4ab@gregkh>
Date: Thu, 27 Feb 2025 12:03:17 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21820: tty: xilinx_uartps: split sysrq handling

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.

The Linux kernel CVE team has assigned CVE-2025-21820 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.6 with commit 74ea66d4ca061a3cd4c0e924e51b60e924644852 and fixed in 6.1.129 with commit de5bd24197bd9ee37ec1e379a3d882bbd15c5065
	Issue introduced in 4.6 with commit 74ea66d4ca061a3cd4c0e924e51b60e924644852 and fixed in 6.6.78 with commit 8ea0e7b3d7b8f2f0fc9db491ff22a0abe120801c
	Issue introduced in 4.6 with commit 74ea66d4ca061a3cd4c0e924e51b60e924644852 and fixed in 6.12.14 with commit 9b88a7c4584ba67267a051069b8abe44fc9595b2
	Issue introduced in 4.6 with commit 74ea66d4ca061a3cd4c0e924e51b60e924644852 and fixed in 6.13.3 with commit 4410dba9807a17a93f649a9f5870ceaf30a675a3
	Issue introduced in 4.6 with commit 74ea66d4ca061a3cd4c0e924e51b60e924644852 and fixed in 6.14-rc1 with commit b06f388994500297bb91be60ffaf6825ecfd2afe

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-21820
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/tty/serial/xilinx_uartps.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/de5bd24197bd9ee37ec1e379a3d882bbd15c5065
	https://git.kernel.org/stable/c/8ea0e7b3d7b8f2f0fc9db491ff22a0abe120801c
	https://git.kernel.org/stable/c/9b88a7c4584ba67267a051069b8abe44fc9595b2
	https://git.kernel.org/stable/c/4410dba9807a17a93f649a9f5870ceaf30a675a3
	https://git.kernel.org/stable/c/b06f388994500297bb91be60ffaf6825ecfd2afe