linux-kernel - [PATCH 4.4 11/26] tty/serial: atmel: fix race condition (TX+DMA)

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Date:   Thu,  6 Apr 2017 10:38:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Richard Genoud <richard.genoud@...il.com>
Subject: [PATCH 4.4 11/26] tty/serial: atmel: fix race condition (TX+DMA)

4.4-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
@@ -1987,6 +1987,11 @@ static void atmel_flush_buffer(struct ua
 		atmel_uart_writel(port, ATMEL_PDC_TCR, 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;
 }
 
 /*