Re: [PATCH] serial: fsl_lpuart: fix rx buffer and DMA map leaks in start_rx_dma

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

On Mon, Apr 20, 2026 at 07:29:03PM +0530, Shitalkumar Gandhi wrote:
> lpuart_start_rx_dma() allocates sport->rx_ring.buf with kzalloc() and
> then maps a scatterlist via dma_map_sg().  On three subsequent error
> paths the function returns directly without releasing those resources:
>
>   - when dma_map_sg() returns 0 (-EINVAL):
>       ring->buf is leaked.
>   - when dmaengine_slave_config() fails:
>       ring->buf and the DMA mapping are leaked.
>   - when dmaengine_prep_dma_cyclic() returns NULL:
>       ring->buf and the DMA mapping are leaked.
>
> The sole cleanup path, lpuart_dma_rx_free(), is only reached when
> lpuart_dma_rx_use is set, and the caller lpuart_rx_dma_startup() clears
> that flag on failure of lpuart_start_rx_dma().  So these resources are
> permanently leaked on every failure in this function.  Repeated port
> open/close or termios changes under error conditions will slowly consume
> memory and leave stale streaming DMA mappings behind.
>
> Fix it by introducing two error labels that unmap the scatterlist and
> free the ring buffer as appropriate.  While here, replace the misleading
> -EFAULT (bad userspace pointer) returned when dmaengine_prep_dma_cyclic()
> fails with the more accurate -ENOMEM, matching how other dmaengine users
> in the tree treat this failure.
>
> No functional change on the success path.
>
> Fixes: 5887ad43ee02 ("tty: serial: fsl_lpuart: Use cyclic DMA for Rx")
> Cc: stable@vger.kernel.org
>
> Signed-off-by: Shitalkumar Gandhi <shitalkumar.gandhi@cambiumnetworks.com>
> ---

Reviewed-by: Frank Li <Frank.Li@nxp.com>

>  drivers/tty/serial/fsl_lpuart.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
> index f36d50fe056f..296a096be351 100644
> --- a/drivers/tty/serial/fsl_lpuart.c
> +++ b/drivers/tty/serial/fsl_lpuart.c
> @@ -1376,7 +1376,8 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
>
>  	if (!nent) {
>  		dev_err(sport->port.dev, "DMA Rx mapping error\n");
> -		return -EINVAL;
> +		ret = -EINVAL;
> +		goto err_free_buf;
>  	}
>
>  	dma_rx_sconfig.src_addr = lpuart_dma_datareg_addr(sport);
> @@ -1388,7 +1389,7 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
>  	if (ret < 0) {
>  		dev_err(sport->port.dev,
>  				"DMA Rx slave config failed, err = %d\n", ret);
> -		return ret;
> +		goto err_unmap_sg;
>  	}
>
>  	sport->dma_rx_desc = dmaengine_prep_dma_cyclic(chan,
> @@ -1399,7 +1400,8 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
>  				 DMA_PREP_INTERRUPT);
>  	if (!sport->dma_rx_desc) {
>  		dev_err(sport->port.dev, "Cannot prepare cyclic DMA\n");
> -		return -EFAULT;
> +		ret = -ENOMEM;
> +		goto err_unmap_sg;
>  	}
>
>  	sport->dma_rx_desc->callback = lpuart_dma_rx_complete;
> @@ -1423,6 +1425,13 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
>  	}
>
>  	return 0;
> +
> +err_unmap_sg:
> +	dma_unmap_sg(chan->device->dev, &sport->rx_sgl, 1, DMA_FROM_DEVICE);
> +err_free_buf:
> +	kfree(ring->buf);
> +	ring->buf = NULL;
> +	return ret;
>  }
>
>  static void lpuart_dma_rx_free(struct uart_port *port)
> --
> 2.25.1
>