linux-kernel - [PATCH v4 5/5] serial/8250: Only use fifo after the port is initialized in console

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Date:   Wed, 16 Mar 2022 11:36:44 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        Wander Lairson Costa <wander@...hat.com>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Serge Semin <fancer.lancer@...il.com>,
        Lukas Wunner <lukas@...ner.de>,
        Pali Rohár <pali@...nel.org>,
        linux-serial@...r.kernel.org (open list:SERIAL DRIVERS),
        linux-kernel@...r.kernel.org (open list)
Cc:     rostedt@...dmis.org, senozhatsky@...omium.org,
        andre.goddard@...il.com, sudipm.mukherjee@...il.com,
        andy.shevchenko@...il.com, David.Laight@...lab.com,
        jonathanh@...dia.com, phil@...pberrypi.com
Subject: [PATCH v4 5/5] serial/8250: Only use fifo after the port is initialized in console_write

The serial driver set the value of uart_8250_port.fcr in the function
serial8250_config_port, but only writes the value to the controller
register later in the initalization code.

That opens a small window in which is not safe to use the fifo for
console write.

Make sure the port is initialized correctly before reading the FCR
cached value.

Unfortunately, I lost track of who originally reported the issue. If
s/he is reading this, please speak up so I can give you the due credit.

Signed-off-by: Wander Lairson Costa <wander@...hat.com>
---
 drivers/tty/serial/8250/8250_port.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 4acf620be241..7e2227161555 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -3416,6 +3416,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 		!(up->capabilities & UART_CAP_MINI) &&
 		up->tx_loadsz > 1 &&
 		(up->fcr & UART_FCR_ENABLE_FIFO) &&
+		test_bit(TTY_PORT_INITIALIZED, &port->state->port.iflags) &&
 		/*
 		 * After we put a data in the fifo, the controller will send
 		 * it regardless of the CTS state. Therefore, only use fifo
-- 
2.35.1