linux-kernel - Re: [PATCH] serial: pch_uart: potential dereference of null pointer

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Date:   Thu, 16 Dec 2021 11:18:29 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     jirislaby@...nel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: pch_uart: potential dereference of null pointer

On Thu, Dec 16, 2021 at 05:44:08PM +0800, Jiasheng Jiang wrote:
> The return value of dma_alloc_coherent() needs to be checked.
> To avoid dereference of null pointer in case of the failure of alloc.
> 
> Fixes: ab4382d27412 ("tty: move drivers/serial/ to drivers/tty/serial/")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>  drivers/tty/serial/pch_uart.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
> index f0351e6f0ef6..2ee1c4d6f177 100644
> --- a/drivers/tty/serial/pch_uart.c
> +++ b/drivers/tty/serial/pch_uart.c
> @@ -745,6 +745,12 @@ static void pch_request_dma(struct uart_port *port)
>  	/* Get Consistent memory for DMA */
>  	priv->rx_buf_virt = dma_alloc_coherent(port->dev, port->fifosize,
>  				    &priv->rx_buf_dma, GFP_KERNEL);
> +	if (!priv->rx_buf_virt) {
> +		dma_release_channel(priv->chan_tx);
> +		priv->chan_tx = NULL;
> +		return;

You are not returning an error, what happens when this buffer is later
attempted to be used?

How did you test this change?

thanks,

greg k-h