Re: HCI core error recovery.

On Mon, Feb 14, 2011 at 4:23 PM, Andrei Warkentin [off-list ref] wrote:

On Sat, Feb 12, 2011 at 12:47 AM, Andrei Warkentin [off-list ref] wrote:

quoted

On Fri, Feb 11, 2011 at 5:07 PM, Andrei Warkentin [off-list ref] wrote:

quoted

Dear List,

I've run into an interesting problem. Excuse me in advance if this was
already covered here, or for my explanations, since I'm not too
familiar with overall flow within BlueZ or Bluetooth specifics...
We've had some hardware config issues that resulted in garbage/malformed
messages arriving via H4 into the HCI layer. We've since resolved
these, but it got me thinking. The issues would result in certain HCI
messages being missed, including occasionally disconnect events being
missed, and a subsequent connect event would result in a double add.

I was thinking about how to fix at the very least the crash. The sysfs
object is created as a last step after getting a "connection
completed" HCI message, I think. What I am unsure about is if it's
safe to just ignore the add if there is already a sysfs entry...

So I would think the HCI core needs some resiliency against
bad/malignant bluetooth controllers, and perform error
recovery/resynchronization. Perhaps maybe there is room for a virtual
hci controller that just injects various message types to see how well
the core can cope?

Thanks in advance,
A

To further explain the issue, here is what was happening -

0) A BT device is paired.
1) Host goes into sleep mode.
2) BT device turns off.
3) Host wakes up due to BT waking the host. Due to UART resume issues,
HCI message corrupted. hci_disconn_complete_evt never gets called.
4) BT device turns on.
5) devref gets incremented in  hci_conn_complete_evt, and is now 2.
6) BT device turns off. hci_disconn_complete_evt is called, conn hash
is deleted, but sysfs entry not cleaned up since
atomic_dec_and_test(&conn->devref) != 0.
7) BT device turns on. sysfs add fails since it never was cleaned up.

The attached patch takes care of that. I'm not too familiar with BlueZ
(or bluetooth :-(), so I would like your feedback. In particular, I am
unsure about sync connections.
The primary issue overall is that HCI core doesn't handle HCI issues
(whether caused by transport issues, or bad/malicious BT controller).
I am curious if there are other ways to break the core.

Thanks,
A

Anyone?

Anyone? Who should I talk to about HCI?