[PATCH 1/8] serdev: ttyport: add missing receive_buf sanity checks

Johan Hovold
2017-11-03T14:31:19Z

The receive_buf tty-port callback should return the number of bytes
accepted and must specifically never return a negative errno (or a value
larger than the buffer size) to the tty layer.

A serdev driver not providing a receive_buf callback would currently
cause the flush_to_ldisc() worker to spin in a tight loop when the tty
buffer pointers are incremented with -EINVAL (-22) after data has been
received.

A serdev driver occasionally returning a negative errno (or a too large
byte count) could cause information leaks or crashes when accessing
memory outside the tty buffers in consecutive callbacks.

Fixes: cd6484e1830b ("serdev: Introduce new bus for serial attached devices")
Cc: stable <stable@vger.kernel.org> # 4.11
Signed-off-by: Johan Hovold <johan@kernel.org>
---
drivers/tty/serdev/serdev-ttyport.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serdev/serdev-ttyport.c b/drivers/tty/serdev/serdev-ttyport.c
index 5b09ce920117..b8bc60a251c6 100644
--- a/drivers/tty/serdev/serdev-ttyport.c
+++ b/drivers/tty/serdev/serdev-ttyport.c
@@ -35,11 +35,22 @@ static int ttyport_receive_buf(struct tty_port *port, const unsigned char *cp,
{
struct serdev_controller *ctrl = port->client_data;
struct serport *serport = serdev_controller_get_drvdata(ctrl);
+ int ret;

if (!test_bit(SERPORT_ACTIVE, &serport->flags))
return 0;

- return serdev_controller_receive_buf(ctrl, cp, count);
+ ret = serdev_controller_receive_buf(ctrl, cp, count);
+
+ dev_WARN_ONCE(&ctrl->dev, ret < 0 || ret > count,
+ "receive_buf returns %d (count = %zu)\n",
+ ret, count);
+ if (ret < 0)
+ return 0;
+ else if (ret > count)
+ return count;
+
+ return ret;
}

static void ttyport_write_wakeup(struct tty_port *port)
--
2.15.0