linux-kernel - [PATCH] tty: serial: owl: Fix data race in owl_uart

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Date:   Thu, 17 Jun 2021 16:34:43 +0530
From:   Saubhik Mukherjee <saubhik.mukherjee@...il.com>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org
Cc:     Saubhik Mukherjee <saubhik.mukherjee@...il.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org, andrianov@...ras.ru
Subject: [PATCH] tty: serial: owl: Fix data race in owl_uart_remove

Suppose the driver is registered and a UART port is added. Once an
application opens the port, owl_uart_startup is called which registers
the interrupt handler owl_uart_irq.

We could have the following race condition:

When device is removed, owl_uart_remove is called, which calls
uart_remove_one_port, which calls owl_uart_release_port, which writes
NULL to port->membase. At this point parallely, an interrupt could be
handled by owl_uart_irq which reads port->membase.

This is because it is possible to remove device without closing a port.
Thus, we need to check it and call owl_uart_shutdown in owl_uart_remove.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Saubhik Mukherjee <saubhik.mukherjee@...il.com>
---
 drivers/tty/serial/owl-uart.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/owl-uart.c b/drivers/tty/serial/owl-uart.c
index 91f1eb0058d7..ac4e3aae2719 100644
--- a/drivers/tty/serial/owl-uart.c
+++ b/drivers/tty/serial/owl-uart.c
@@ -751,8 +751,15 @@ static int owl_uart_probe(struct platform_device *pdev)
 static int owl_uart_remove(struct platform_device *pdev)
 {
 	struct owl_uart_port *owl_port = platform_get_drvdata(pdev);
+	struct uart_port *port = &owl_port->port;

-	uart_remove_one_port(&owl_uart_driver, &owl_port->port);
+	/* It is possible to release device without closing a port.
+	 * Thus, need to check it and call shutdown.
+	 */
+	if (owl_uart_read(port, OWL_UART_CTL) & OWL_UART_CTL_EN)
+		owl_uart_shutdown(port);
+
+	uart_remove_one_port(&owl_uart_driver, port);
 	owl_uart_ports[pdev->id] = NULL;
 	clk_disable_unprepare(owl_port->clk);

-- 
2.30.2