tty/serial: atmel: fix race condition (TX+DMA)

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@microchip.com>
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index fabbe76203bb..159c71e67716 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1938,6 +1938,11 @@ static void atmel_flush_buffer(struct uart_port *port)
                 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;
 }
 
 /*