Re: [Bluez PATCH v6] bluetooth: secure bluetooth stack from bluedump attack

Hi Howard,

Attack scenario:
1. A Chromebook (let's call this device A) is paired to a legitimate
  Bluetooth classic device (e.g. a speaker) (let's call this device
  B).
2. A malicious device (let's call this device C) pretends to be the
  Bluetooth speaker by using the same BT address.
3. If device A is not currently connected to device B, device A will
  be ready to accept connection from device B in the background
  (technically, doing Page Scan).
4. Therefore, device C can initiate connection to device A
  (because device A is doing Page Scan) and device A will accept the
  connection because device A trusts device C's address which is the
  same as device B's address.
5. Device C won't be able to communicate at any high level Bluetooth
  profile with device A because device A enforces that device C is
  encrypted with their common Link Key, which device C doesn't have.
  But device C can initiate pairing with device A with just-works
  model without requiring user interaction (there is only pairing
  notification). After pairing, device A now trusts device C with a
  new different link key, common between device A and C.
6. From now on, device A trusts device C, so device C can at anytime
  connect to device A to do any kind of high-level hijacking, e.g.
  speaker hijack or mouse/keyboard hijack.

Since we don't know whether the repairing is legitimate or not,
leave the decision to user space if all the conditions below are met.
- the pairing is initialized by peer
- the authorization method is just-work
- host already had the link key to the peer

Signed-off-by: Howard Chung <redacted>
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Changes in v6:
- Fix passkey uninitialized issue

since I already applied v5, can you send a delta-patch. And please add a comment for using 0 as passkey and why that is correct.

Regards

Marcel