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Subject[PATCH 4.14 003/164] serdev: ttyport: add missing receive_buf sanity checks
4.14-stable review patch.  If anyone has any objections, please let me know.


From: Johan Hovold <>

commit eb281683621b71ab9710d9dccbbef0c2e1769c97 upstream.

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

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")
Signed-off-by: Johan Hovold <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/tty/serdev/serdev-ttyport.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

--- a/drivers/tty/serdev/serdev-ttyport.c
+++ b/drivers/tty/serdev/serdev-ttyport.c
@@ -35,11 +35,22 @@ static int ttyport_receive_buf(struct tt
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)

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