staging: speakup: fix tty-operation NULL derefs

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 <stable@vger.kernel.org>     # 4.13
Cc: Okash Khawaja <okash.khawaja@gmail.com>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/speakup/spk_ttyio.c b/drivers/staging/speakup/spk_ttyio.c
index 4d7d8f2..71edd3c 100644 (file)
--- a/drivers/staging/speakup/spk_ttyio.c
+++ b/drivers/staging/speakup/spk_ttyio.c
@@ -246,7 +246,8 @@ 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);
 }
 
@@ -258,7 +259,8 @@ static void spk_ttyio_tiocmset(unsigned int set, unsigned int clear)
                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);
 }