linux-kernel - Re: [PATCH 3.18 049/124] tty/serial: atmel: fix race condition (TX+DMA)

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Date:   Thu, 20 Apr 2017 09:46:03 +0200
From:   Richard Genoud <richard.genoud@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Nicolas Ferre <nicolas.ferre@...rochip.com>
Subject: Re: [PATCH 3.18 049/124] tty/serial: atmel: fix race condition
 (TX+DMA)

On 20/04/2017 08:35, Greg Kroah-Hartman wrote:
> 3.18-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Richard Genoud <richard.genoud@...il.com>
> 
> commit 31ca2c63fdc0aee725cbd4f207c1256f5deaabde upstream.
> 
> If uart_flush_buffer() is called between atmel_tx_dma() and
> atmel_complete_tx_dma(), the circular buffer has been cleared, but not
> atmel_port->tx_len.
> That leads to a circular buffer overflow (dumping (UART_XMIT_SIZE -
> atmel_port->tx_len) bytes).
> 
> Tested-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
> Signed-off-by: Richard Genoud <richard.genoud@...il.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> ---
>  drivers/tty/serial/atmel_serial.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -1867,6 +1867,11 @@ static void atmel_flush_buffer(struct ua
>  		UART_PUT_TCR(port, 0);
>  		atmel_port->pdc_tx.ofs = 0;
>  	}
> +	/*
> +	 * in uart_flush_buffer(), the xmit circular buffer has just
> +	 * been cleared, so we have to reset tx_len accordingly.
> +	 */
> +	atmel_port->tx_len = 0;
>  }
>  
>  /*
> 
> 
Hi,
This won't compile on 3.18 kernel since ->tx_len doesn't exist yet.

Here is the backported version of this patch:
Thanks !
======================

commit 31ca2c63fdc0aee725cbd4f207c1256f5deaabde upstream.

If uart_flush_buffer() is called between atmel_tx_dma() and
atmel_complete_tx_dma(), the circular buffer has been cleared, but not
its length.
That leads to a circular buffer overflow (dumping (UART_XMIT_SIZE -
sg_dma_len(&atmel_port->sg_tx)) bytes).

Signed-off-by: Richard Genoud <richard.genoud@...il.com>
---
 drivers/tty/serial/atmel_serial.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index daaed7c79e4f..a10c778be2ad 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1867,6 +1867,11 @@ static void atmel_flush_buffer(struct uart_port *port)
 		UART_PUT_TCR(port, 0);
 		atmel_port->pdc_tx.ofs = 0;
 	}
+	/*
+	 * in uart_flush_buffer(), the xmit circular buffer has just
+	 * been cleared, so we have to reset its length accordingly.
+	 */
+	sg_dma_len(&atmel_port->sg_tx) = 0;
 }
 
 /*