[PATCH 4.4 017/137] serial: omap: Prevent DoS using unprivileged ioctl(TIOCSRS485)

Greg Kroah-Hartman
2016-02-24T04:40:38Z

From: Peter Hurley <peter@hurleysoftware.com>

commit 308bbc9ab838d0ace0298268c7970ba9513e2c65 upstream.

The omap-serial driver emulates RS485 delays using software timers,
but neglects to clamp the input values from the unprivileged
ioctl(TIOCSRS485). Because the software implementation busy-waits,
malicious userspace could stall the cpu for ~49 days.

Clamp the input values to < 100ms.

Fixes: 4a0ac0f55b18 ("OMAP: add RS485 support")
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/tty/serial/omap-serial.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -1343,7 +1343,7 @@ static inline void serial_omap_add_conso

/* Enable or disable the rs485 support */
static int
-serial_omap_config_rs485(struct uart_port *port, struct serial_rs485 *rs485conf)
+serial_omap_config_rs485(struct uart_port *port, struct serial_rs485 *rs485)
{
struct uart_omap_port *up = to_uart_omap_port(port);
unsigned int mode;
@@ -1356,8 +1356,12 @@ serial_omap_config_rs485(struct uart_por
up->ier = 0;
serial_out(up, UART_IER, 0);

+ /* Clamp the delays to [0, 100ms] */
+ rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
+ rs485->delay_rts_after_send = min(rs485->delay_rts_after_send, 100U);
+
/* store new config */
- port->rs485 = *rs485conf;
+ port->rs485 = *rs485;

/*
* Just as a precaution, only allow rs485