tty: Handle problem if line discipline does not have receive_buf

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>

1 files changed, 2 insertions, 1 deletions

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;
 }