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>

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 23c6fd23842295de47b5ec328316e5de8c435b76..21ffcce16927164a279cb0afa8300d4430942910 100644 (file)
--- 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;
 }