[PATCH 4.4 095/210] tty: Fix GPF in flush_to_ldisc(), part 2

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>

commit f33798deecbd59a2955f40ac0ae2bc7dff54c069 upstream.

commit 9ce119f318ba ("tty: Fix GPF in flush_to_ldisc()") fixed a
GPF caused by a line discipline which does not define a receive_buf()
method.

However, the vt driver (and speakup driver also) pushes selection
data directly to the line discipline receive_buf() method via
tty_ldisc_receive_buf(). Fix the same problem in tty_ldisc_receive_buf().

Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 include/linux/tty.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -594,7 +594,7 @@ static inline int tty_ldisc_receive_buf(
 		count = ld->ops->receive_buf2(ld->tty, p, f, count);
 	else {
 		count = min_t(int, count, ld->tty->receive_room);
-		if (count)
+		if (count && ld->ops->receive_buf)
 			ld->ops->receive_buf(ld->tty, p, f, count);
 	}
 	return count;