bluetooth: Fix missing NULL check

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
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 998833d93c13..17361bad46dd 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;