[PATCH 5.15.y 2/2] serial: imx: serialize imx_uart_ports[] lifetime

[Sasha Levin <sashal@kernel.org>]

From: Karl Mehltretter <kmehltretter@gmail.com>

[ Upstream commit 8b0b29fdcb47907ae0296b8fe829e918e05e300f ]

imx_uart_probe() publishes its devm-allocated port in imx_uart_ports[]
before uart_add_one_port() because console setup uses the table. The entry
is not cleared when adding the port fails or after removal, leaving a
dangling pointer.

A sibling probe can register the shared console through that stale entry.
This was reproduced under KASAN on QEMU mcimx6ul-evk by unbinding a
sibling UART, unbinding the console UART and rebinding the sibling.

Keep the entry valid through uart_remove_one_port(), then clear it. Protect
port addition and removal together with their table updates so sibling
operations cannot interleave. Reject an occupied slot rather than
clobbering an active port during a duplicate-line probe.

Fixes: dbff4e9ea2e8 ("IMX UART: remove statically initialized tables")
Fixes: 9f322ad064f9 ("imx: serial: handle initialisation failure correctly")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/all/20260719162850.043B41F000E9@smtp.kernel.org
Link: https://lore.kernel.org/all/20260719222501.CB4CB1F000E9@smtp.kernel.org
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-fable-5
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260731181844.11330-6-kmehltretter@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ replaced scoped_guard() with explicit mutex_lock()/mutex_unlock() calls for GNU89 compatibility ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/imx.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index ba64da1ca7b19..11338cb7b2112 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -21,6 +21,7 @@
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/ktime.h>
+#include <linux/mutex.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/rational.h>
 #include <linux/slab.h>
@@ -2005,6 +2006,9 @@ static const struct uart_ops imx_uart_pops = {
 
 static struct imx_port *imx_uart_ports[UART_NR];
 
+/* Held across uart_add/remove_one_port(); console callbacks must not take it. */
+static DEFINE_MUTEX(imx_uart_ports_lock);
+
 #if IS_ENABLED(CONFIG_SERIAL_IMX_CONSOLE)
 static void imx_uart_console_putchar(struct uart_port *port, int ch)
 {
@@ -2472,11 +2476,18 @@ static int imx_uart_probe(struct platform_device *pdev)
 		}
 	}
 
-	imx_uart_ports[sport->port.line] = sport;
-
 	platform_set_drvdata(pdev, sport);
 
-	ret = uart_add_one_port(&imx_uart_uart_driver, &sport->port);
+	mutex_lock(&imx_uart_ports_lock);
+	if (imx_uart_ports[sport->port.line]) {
+		ret = -EBUSY;
+	} else {
+		imx_uart_ports[sport->port.line] = sport;
+		ret = uart_add_one_port(&imx_uart_uart_driver, &sport->port);
+		if (ret)
+			imx_uart_ports[sport->port.line] = NULL;
+	}
+	mutex_unlock(&imx_uart_ports_lock);
 
 err_clk:
 	clk_disable_unprepare(sport->clk_ipg);
@@ -2488,7 +2499,9 @@ static void imx_uart_remove(struct platform_device *pdev)
 {
 	struct imx_port *sport = platform_get_drvdata(pdev);
 
+	guard(mutex)(&imx_uart_ports_lock);
 	uart_remove_one_port(&imx_uart_uart_driver, &sport->port);
+	imx_uart_ports[sport->port.line] = NULL;
 }
 
 static void imx_uart_restore_context(struct imx_port *sport)
-- 
2.53.0