linux-kernel - [PATCH] serial: 8250: always disable IRQ during THRE test

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20251014114727.1186-1-zhangpeng.00@bytedance.com>
Date: Tue, 14 Oct 2025 19:47:27 +0800
From: Peng Zhang <zhangpeng.00@...edance.com>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	songmuchun@...edance.com,
	Peng Zhang <zhangpeng.00@...edance.com>
Subject: [PATCH] serial: 8250: always disable IRQ during THRE test

commit 039d4926379b ("serial: 8250: Toggle IER bits on only after irq
has been set up") moved IRQ setup before the THRE test, so the interrupt
handler can run during the test and race with its IIR reads. This can
produce wrong THRE test results and cause spurious registration of the
serial8250_backup_timeout timer. Unconditionally disable the IRQ for the
short duration of the test and re-enable it afterwards to avoid the race.

Fixes: 039d4926379b ("serial: 8250: Toggle IER bits on only after irq has been set up")
Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
---
 drivers/tty/serial/8250/8250_port.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 719faf92aa8a..addeef7a0d59 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2147,8 +2147,7 @@ static void serial8250_THRE_test(struct uart_port *port)
 	if (up->port.flags & UPF_NO_THRE_TEST)
 		return;
 
-	if (port->irqflags & IRQF_SHARED)
-		disable_irq_nosync(port->irq);
+	disable_irq_nosync(port->irq);
 
 	/*
 	 * Test for UARTs that do not reassert THRE when the transmitter is idle and the interrupt
@@ -2170,8 +2169,7 @@ static void serial8250_THRE_test(struct uart_port *port)
 		serial_port_out(port, UART_IER, 0);
 	}
 
-	if (port->irqflags & IRQF_SHARED)
-		enable_irq(port->irq);
+	enable_irq(port->irq);
 
 	/*
 	 * If the interrupt is not reasserted, or we otherwise don't trust the iir, setup a timer to
-- 
2.20.1