From 27cfb3a53be46a54ec5e0bd04e51995b74c90343 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Sun, 20 Jan 2019 10:46:58 +0100
Subject: [PATCH] tty: Handle problem if line discipline does not have receive_buf
Git-commit: 27cfb3a53be46a54ec5e0bd04e51995b74c90343
Patch-mainline: v5.0-rc4
References: bsc#1051510

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@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/tty/tty_io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 23c6fd238422..21ffcce16927 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2189,7 +2189,8 @@ static int tiocsti(struct tty_struct *tty, char __user *p)
 	ld = tty_ldisc_ref_wait(tty);
 	if (!ld)
 		return -EIO;
-	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;
 }
-- 
2.16.4