Hi David,

On Fri, Mar 09, 2012 at 02:44:30PM +0100, David Herrmann wrote:

On Wed, Mar 7, 2012 at 5:01 PM, Johan Hovold [off-list ref] wrote:

quoted

Do not close protocol driver until device has been unregistered.

This fixes a race between tty_close and hci_dev_open which can result in
a NULL-pointer dereference.

The line discipline closes the protocol driver while we may still have
hci_dev_open sleeping on the req_lock mutex resulting in a NULL-pointer
dereference when lock is acquired and hci_init_req called.

[...]

quoted

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 0711448..6946081 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c

@@ -310,11 +310,11 @@ static void hci_uart_tty_close(struct tty_struct *tty)

                       hci_uart_close(hdev);

               if (test_and_clear_bit(HCI_UART_PROTO_SET, &hu->flags)) {
-                       hu->proto->close(hu);
                       if (hdev) {
                               hci_unregister_dev(hdev);
                               hci_free_dev(hdev);
                       }
+                       hu->proto->close(hu);
               }
       }
 }

I can confirm this. hci_uart_set_proto() opens the proto before it
registers the hci device. Hence, we should also unregister the hci
device before closing the proto. I also looked whether this introduces
other race conditions but no proto-callback can be called here as they
are all protected by the tty-layer which synchronizes all
tty-callbacks. Therefore, I think this is the correct fix.

We can apply this to stable even without the "destruct"-fixes from me
as hu->proto->$cb$() doesn't care whether hdev is valid or not. I
don't think the destruct-fixes are important enough to send them to
stable.

Unfortunately hu is is not valid once hci_unregister returns as it will
call the destruct callback. So my patch depends on changing this
behaviour first. (I could also store a pointer to the protocol before
calling unregister in my patch.)

Secondly, I must disagree with you regarding whether the memory leak you
found is critical enough to be added to the stable trees. We're leaking
kernel memory in a deterministic and easily triggered way which could be
exploited by a malicious user.

Reviewed-by: David Herrmann <redacted>

Thanks,
Johan