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

Greg Kroah-Hartman
2017-04-06T08:39:50Z

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

/*