From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Sun, 20 Jan 2019 09:46:58 +0000 (+0100)
Subject: tty: Handle problem if line discipline does not have receive_buf
X-Git-Tag: v4.19.19~58
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=80250b48803ab0aa3eb8e0d798a4742b26ef84d9;p=users%2Fdwmw2%2Flinux.git

tty: Handle problem if line discipline does not have receive_buf

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@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 052ec16a4e84e..e7d192ebecd7d 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2188,7 +2188,8 @@ 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;
 }