[1/2] Bluetooth: hci_event: Ignore NULL link key

Commit Message

joeyli Oct. 1, 2023, 8:08 a.m. UTC

This change is used to relieve CVE-2020-26555. The description of the
CVE:

Bluetooth legacy BR/EDR PIN code pairing in Bluetooth Core Specification
1.0B through 5.2 may permit an unauthenticated nearby device to spoof
the BD_ADDR of the peer device to complete pairing without knowledge
of the PIN. [1]

The detail of this attack is in IEEE paper:
BlueMirror: Reflections on Bluetooth Pairing and Provisioning Protocols
[2]

It's a reflection attack. The paper mentioned that attacker can induce
the attacked target to generate null link key (zero key) without PIN
code. In BR/EDR, the key generation is actually handled in the controller
which is below HCI.

Thus, we can ignore null link key in the handler of "Link Key Notification
event" to relieve the attack. A similar implementation also shows in
btstack project. [3]

v3: Drop the connection when null link key be detected.

v2:
- Used Link: tag instead of Closes:
- Used bt_dev_dbg instead of BT_DBG
- Added Fixes: tag

Fixes: 55ed8ca10f35 ("Bluetooth: Implement link key handling for the management interface")
Link: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26555 [1]
Link: https://ieeexplore.ieee.org/abstract/document/9474325/authors#authors [2]
Link: https://github.com/bluekitchen/btstack/blob/master/src/hci.c#L3722 [3]
Signed-off-by: Lee, Chun-Yi <[e-mail]>
---
 net/bluetooth/hci_event.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

[e-mail] Oct. 1, 2023, 8:44 a.m. UTC | #1

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=789096

---Test result---

Test Summary:
CheckPatch                    PASS      0.77 seconds
GitLint                       PASS      0.32 seconds
SubjectPrefix                 PASS      0.10 seconds
BuildKernel                   PASS      43.13 seconds
CheckAllWarning               PASS      46.91 seconds
CheckSparse                   WARNING   53.60 seconds
CheckSmatch                   WARNING   140.37 seconds
BuildKernel32                 PASS      41.66 seconds
TestRunnerSetup               PASS      622.54 seconds
TestRunner_l2cap-tester       PASS      38.78 seconds
TestRunner_iso-tester         PASS      82.16 seconds
TestRunner_bnep-tester        PASS      13.74 seconds
TestRunner_mgmt-tester        FAIL      251.73 seconds
TestRunner_rfcomm-tester      PASS      21.30 seconds
TestRunner_sco-tester         PASS      24.23 seconds
TestRunner_ioctl-tester       PASS      23.16 seconds
TestRunner_mesh-tester        PASS      16.89 seconds
TestRunner_smp-tester         PASS      20.09 seconds
TestRunner_userchan-tester    PASS      15.21 seconds
IncrementalBuild              PASS      40.23 seconds

Details
##############################
Test: CheckSparse - WARNING
Desc: Run sparse tool with linux kernel
Output:
net/bluetooth/hci_event.c: note: in included file (through include/net/bluetooth/hci_core.h):
##############################
Test: CheckSmatch - WARNING
Desc: Run smatch tool with source
Output:
net/bluetooth/hci_event.c: note: in included file (through include/net/bluetooth/hci_core.h):
##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 497, Passed: 496 (99.8%), Failed: 1, Not Run: 0

Failed Test Cases
LL Privacy - Unpair 1                                Timed out    2.016 seconds


---
Regards,
Linux Bluetooth

Patch

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 95816a938cea..a20a94e85b1a 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -4692,6 +4692,14 @@  static void hci_link_key_notify_evt(struct hci_dev *hdev, void *data,
 	if (!conn)
 		goto unlock;
 
+	/* Ignore NULL link key against CVE-2020-26555 */
+	if (!memcmp(ev->link_key, ZERO_KEY, HCI_LINK_KEY_SIZE)) {
+		bt_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) for %pMR", &ev->bdaddr);
+		hci_disconnect(conn, HCI_ERROR_AUTH_FAILURE);
+		hci_conn_drop(conn);
+		goto unlock;
+	}
+
 	hci_conn_hold(conn);
 	conn->disc_timeout = HCI_DISCONN_TIMEOUT;
 	hci_conn_drop(conn);