[PATCH] bluetooth: Fix missing NULL check

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

From: Alan Cox <alan@linux.intel.com>

Fortunately this is only exploitable on very unusual hardware.

[Reported a while ago but nothing happened so just fixing it]

Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: stable@kernel.org
---

 drivers/bluetooth/hci_ldisc.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)


diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 74cb6f3..7201482 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -256,9 +256,16 @@ static int hci_uart_tty_open(struct tty_struct *tty)
 
 	BT_DBG("tty %p", tty);
 
+	/* FIXME: This btw is bogus, nothing requires the old ldisc to clear
+	   the pointer */
 	if (hu)
 		return -EEXIST;
 
+	/* Error if the tty has no write op instead of leaving an exploitable
+	   hole */
+	if (tty->ops->write == NULL)
+		return -EOPNOTSUPP;
+
 	if (!(hu = kzalloc(sizeof(struct hci_uart), GFP_KERNEL))) {
 		BT_ERR("Can't allocate control structure");
 		return -ENFILE;