[PATCH 3.10 219/268] tty/serial: atmel: fix race condition (TX+DMA)

Willy Tarreau
2017-06-19T19:20:33Z

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>
[rg] backport to 3.12
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
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 82127ac..41d1df5 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1090,6 +1090,11 @@ 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;
}

/*
--
2.8.0.rc2.1.gbe9624a