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

rgenoud · gregkh · commit 74b8fc017d76 · 2017-04-08T09:53:31.000+02:00
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-&gt;tx_len.
That leads to a circular buffer overflow (dumping (UART_XMIT_SIZE -
atmel_port-&gt;tx_len) bytes).

Tested-by: Nicolas Ferre &lt;nicolas.ferre@microchip.com&gt;
Signed-off-by: Richard Genoud &lt;richard.genoud@gmail.com&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
@@ -1987,6 +1987,11 @@ 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;
 }
 
 /*

Original file line number	Diff line number	Diff line change
`@@ -1987,6 +1987,11 @@ static void atmel_flush_buffer(struct uart_port *port)`
`1987`	`1987`	`atmel_uart_writel(port, ATMEL_PDC_TCR, 0);`
`1988`	`1988`	`atmel_port->pdc_tx.ofs = 0;`
`1989`	`1989`	`}`
	`1990`	`+ /*`
	`1991`	`+ * in uart_flush_buffer(), the xmit circular buffer has just`
	`1992`	`+ * been cleared, so we have to reset tx_len accordingly.`
	`1993`	`+ */`
	`1994`	`+ atmel_port->tx_len = 0;`
`1990`	`1995`	`}`
`1991`	`1996`
`1992`	`1997`	`/*`