linux-kernel - Re: [PATCH V2 1/2] serial: sprd: Assign sprd_port after initialized to avoid wrong access

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Message-ID: <7c7e062f-40d2-a3d9-6a25-0ef3defe2caf@linux.alibaba.com>
Date:   Thu, 20 Jul 2023 14:57:34 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Chunyan Zhang <chunyan.zhang@...soc.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     linux-serial@...r.kernel.org, Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/2] serial: sprd: Assign sprd_port after initialized
 to avoid wrong access



On 7/13/2023 11:19 AM, Chunyan Zhang wrote:
> The global pointer 'sprd_port' may not zero when sprd_probe returns
> failure, that is a risk for sprd_port to be accessed afterward, and
> may lead to unexpected errors.
> 
> For example:
> 
> There are two UART ports, UART1 is used for console and configured in
> kernel command line, i.e. "console=";
> 
> The UART1 probe failed and the memory allocated to sprd_port[1] was
> released, but sprd_port[1] was not set to NULL;
> 
> In UART2 probe, the same virtual address was allocated to sprd_port[2],
> and UART2 probe process finally will go into sprd_console_setup() to
> register UART1 as console since it is configured as preferred console
> (filled to console_cmdline[]), but the console parameters (sprd_port[1])
> belong to UART2.
> 
> So move the sprd_port[] assignment to where the port already initialized
> can avoid the above issue.
> 
> Fixes: b7396a38fb28 ("tty/serial: Add Spreadtrum sc9836-uart driver support")
> Signed-off-by: Chunyan Zhang <chunyan.zhang@...soc.com>
> ---
> V2:
> - Leave sprd_remove() to keep the unrelated code logic the same.
> ---
>   drivers/tty/serial/sprd_serial.c | 25 +++++++++++++++++--------
>   1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/tty/serial/sprd_serial.c b/drivers/tty/serial/sprd_serial.c
> index b58f51296ace..11de338a6122 100644
> --- a/drivers/tty/serial/sprd_serial.c
> +++ b/drivers/tty/serial/sprd_serial.c
> @@ -1106,7 +1106,7 @@ static bool sprd_uart_is_console(struct uart_port *uport)
>   static int sprd_clk_init(struct uart_port *uport)
>   {
>   	struct clk *clk_uart, *clk_parent;
> -	struct sprd_uart_port *u = sprd_port[uport->line];
> +	struct sprd_uart_port *u = container_of(uport, struct sprd_uart_port, port);
>   
>   	clk_uart = devm_clk_get(uport->dev, "uart");
>   	if (IS_ERR(clk_uart)) {
> @@ -1149,22 +1149,22 @@ static int sprd_probe(struct platform_device *pdev)
>   {
>   	struct resource *res;
>   	struct uart_port *up;
> +	struct sprd_uart_port *sport;
>   	int irq;
>   	int index;
>   	int ret;
>   
>   	index = of_alias_get_id(pdev->dev.of_node, "serial");
> -	if (index < 0 || index >= ARRAY_SIZE(sprd_port)) {
> +	if (index < 0 || index >= UART_NR_MAX) {
>   		dev_err(&pdev->dev, "got a wrong serial alias id %d\n", index);
>   		return -EINVAL;
>   	}
>   
> -	sprd_port[index] = devm_kzalloc(&pdev->dev, sizeof(*sprd_port[index]),
> -					GFP_KERNEL);
> -	if (!sprd_port[index])
> +	sport = devm_kzalloc(&pdev->dev, sizeof(*sport), GFP_KERNEL);
> +	if (!sport)
>   		return -ENOMEM;
>   
> -	up = &sprd_port[index]->port;
> +	up = &sport->port;
>   	up->dev = &pdev->dev;
>   	up->line = index;
>   	up->type = PORT_SPRD;
> @@ -1195,7 +1195,7 @@ static int sprd_probe(struct platform_device *pdev)
>   	 * Allocate one dma buffer to prepare for receive transfer, in case
>   	 * memory allocation failure at runtime.
>   	 */
> -	ret = sprd_rx_alloc_buf(sprd_port[index]);
> +	ret = sprd_rx_alloc_buf(sport);
>   	if (ret)
>   		return ret;
>   
> @@ -1208,12 +1208,21 @@ static int sprd_probe(struct platform_device *pdev)
>   	}
>   	sprd_ports_num++;
>   
> +	sprd_port[index] = sport;
> +
>   	ret = uart_add_one_port(&sprd_uart_driver, up);
>   	if (ret)
> -		sprd_remove(pdev);
> +		goto clean_port;
>   
>   	platform_set_drvdata(pdev, up);
>   
> +	return 0;
> +
> +clean_port:
> +	sprd_port[index] = NULL;
> +	sprd_ports_num--;
> +	uart_unregister_driver(&sprd_uart_driver);

I am not sure this is corect, in sprd_remove() it only calls 
uart_unregister_driver() when the 'sprd_ports_num' decreases to 0.

> +	sprd_remove(pdev);

I don't think calling sprd_remove() is helpful here, since we have not 
saved 'up' into the driver data, which means the 'sprd_rx_free_buf(sup)' 
will not be called in sprd_remove().

So, to simplify the code, I think you can just add the 
sprd_rx_free_buf() into the 'clean_port' label:

clean_port:
	sprd_rx_free_buf(sprd_port[index]);
	sprd_port[index] = NULL;
	sprd_ports_num--;
	if (!sprd_ports_num)
		uart_unregister_driver(&sprd_uart_driver);

Then in patch 2, you can move the sprd_rx_free_buf() to the correct 
place to fix another potential leak issue.