[PATCH 4.20 335/352] staging: speakup: fix tty-operation NULL derefs

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

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

From: Johan Hovold <jo...@kernel.org>

commit a1960e0f1639cb1f7a3d94521760fc73091f6640 upstream.

The send_xchar() and tiocmset() tty operations are optional. Add the
missing sanity checks to prevent user-space triggerable NULL-pointer
dereferences.

Fixes: 6b9ad1c742bf ("staging: speakup: add send_xchar, tiocmset and input 
functionality for tty")
Cc: stable <sta...@vger.kernel.org>     # 4.13
Cc: Okash Khawaja <okash.khaw...@gmail.com>
Cc: Samuel Thibault <samuel.thiba...@ens-lyon.org>
Signed-off-by: Johan Hovold <jo...@kernel.org>
Reviewed-by: Samuel Thibault <samuel.thiba...@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/staging/speakup/spk_ttyio.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/staging/speakup/spk_ttyio.c
+++ b/drivers/staging/speakup/spk_ttyio.c
@@ -265,7 +265,8 @@ static void spk_ttyio_send_xchar(char ch
                return;
        }
 
-       speakup_tty->ops->send_xchar(speakup_tty, ch);
+       if (speakup_tty->ops->send_xchar)
+               speakup_tty->ops->send_xchar(speakup_tty, ch);
        mutex_unlock(&speakup_tty_mutex);
 }
 
@@ -277,7 +278,8 @@ static void spk_ttyio_tiocmset(unsigned
                return;
        }
 
-       speakup_tty->ops->tiocmset(speakup_tty, set, clear);
+       if (speakup_tty->ops->tiocmset)
+               speakup_tty->ops->tiocmset(speakup_tty, set, clear);
        mutex_unlock(&speakup_tty_mutex);
 }