Re: [PATCH v3 5/5] serial: imx: serialize imx_uart_ports[] lifetime

[Frank Li <Frank.li@oss.nxp.com>]

On Fri, Jul 31, 2026 at 08:05:19PM +0200, Karl Mehltretter wrote:
> 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>

> Backport note: the removal fix is self-contained. Complete probe-failure
> coverage also requires patch 1. With patch 1, all fallible allocations
> precede console registration, so rollback can safely clear the table.
> Without it, a late allocation failure (only reachable with fault
> injection) can leave the console registered after imx_uart_ports[] is
> cleared, turning the pre-existing use-after-free into a NULL
> dereference.
>
>  drivers/tty/serial/imx.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 251a50c8aa38..b0f34a6e7d4f 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -22,6 +22,7 @@
>  #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>
> @@ -2080,6 +2081,9 @@ 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, unsigned char ch)
>  {
> @@ -2632,11 +2636,19 @@ 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);
> +	scoped_guard(mutex, &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;
> +		}
> +	}
>
>  err_clk:
>  	clk_disable_unprepare(sport->clk_ipg);
> @@ -2648,7 +2660,9 @@ 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
>