[PATCH 3.16 058/202] tty: Handle problem if line discipline does not have receive_buf

[Ben Hutchings]

3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

commit 27cfb3a53be46a54ec5e0bd04e51995b74c90343 upstream.

Some tty line disciplines do not have a receive buf callback, so
properly check for that before calling it.  If they do not have this
callback, just eat the character quietly, as we can't fail this call.

Reported-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/tty/tty_io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2219,7 +2219,8 @@ static int tiocsti(struct tty_struct *tt
 		return -EFAULT;
 	tty_audit_tiocsti(tty, ch);
 	ld = tty_ldisc_ref_wait(tty);
-	ld->ops->receive_buf(tty, &ch, &mbz, 1);
+	if (ld->ops->receive_buf)
+		ld->ops->receive_buf(tty, &ch, &mbz, 1);
 	tty_ldisc_deref(ld);
 	return 0;
 }