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

[Willy Tarreau]

From: Richard Genoud <richard.genoud@xxxxxxxxx>

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@xxxxxxxxxxxxx>
[rg] backport to 3.12
Signed-off-by: Richard Genoud <richard.genoud@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 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