[PATCH v3] Bluetooth: Add more enc key size check

[PATCH v3] Bluetooth: Add more enc key size check

[Alex Lu]

From: Alex Lu <alex_lu@realsil.com.cn>

When we are slave role and receives l2cap conn req when encryption has
started, we should check the enc key size to avoid KNOB attack or BLUFFS
attack.
From SIG recommendation, implementations are advised to reject
service-level connections on an encrypted baseband link with key
strengths below 7 octets.
A simple and clear way to achieve this is to place the enc key size
check in hci_cc_read_enc_key_size()

The btmon log below shows the case that lacks enc key size check.

> HCI Event: Connect Request (0x04) plen 10
        Address: BB:22:33:44:55:99 (OUI BB-22-33)
        Class: 0x480104
          Major class: Computer (desktop, notebook, PDA, organizers)
          Minor class: Desktop workstation
          Capturing (Scanner, Microphone)
          Telephony (Cordless telephony, Modem, Headset)
        Link type: ACL (0x01)
< HCI Command: Accept Connection Request (0x01|0x0009) plen 7
        Address: BB:22:33:44:55:99 (OUI BB-22-33)
        Role: Peripheral (0x01)
> HCI Event: Command Status (0x0f) plen 4
      Accept Connection Request (0x01|0x0009) ncmd 2
        Status: Success (0x00)
> HCI Event: Connect Complete (0x03) plen 11
        Status: Success (0x00)
        Handle: 1
        Address: BB:22:33:44:55:99 (OUI BB-22-33)
        Link type: ACL (0x01)
        Encryption: Disabled (0x00)
...

> HCI Event: Encryption Change (0x08) plen 4
        Status: Success (0x00)
        Handle: 1 Address: BB:22:33:44:55:99 (OUI BB-22-33)
        Encryption: Enabled with E0 (0x01)
< HCI Command: Read Encryption Key Size (0x05|0x0008) plen 2
        Handle: 1 Address: BB:22:33:44:55:99 (OUI BB-22-33)
> HCI Event: Command Complete (0x0e) plen 7
      Read Encryption Key Size (0x05|0x0008) ncmd 2
        Status: Success (0x00)
        Handle: 1 Address: BB:22:33:44:55:99 (OUI BB-22-33)
        Key size: 6
// We should check the enc key size
...

> ACL Data RX: Handle 1 flags 0x02 dlen 12
      L2CAP: Connection Request (0x02) ident 3 len 4
        PSM: 25 (0x0019)
        Source CID: 64
< ACL Data TX: Handle 1 flags 0x00 dlen 16
      L2CAP: Connection Response (0x03) ident 3 len 8
        Destination CID: 64
        Source CID: 64
        Result: Connection pending (0x0001)
        Status: Authorization pending (0x0002)
> HCI Event: Number of Completed Packets (0x13) plen 5
        Num handles: 1
        Handle: 1 Address: BB:22:33:44:55:99 (OUI BB-22-33)
        Count: 1
        #35: len 16 (25 Kb/s)
        Latency: 5 msec (2-7 msec ~4 msec)
< ACL Data TX: Handle 1 flags 0x00 dlen 16
      L2CAP: Connection Response (0x03) ident 3 len 8
        Destination CID: 64
        Source CID: 64
        Result: Connection successful (0x0000)
        Status: No further information available (0x0000)

Signed-off-by: Alex Lu <alex_lu@realsil.com.cn>
Signed-off-by: Max Chou <max.chou@realtek.com>
---
Changes in v3:
  - Use a simple and clear approach according to maintainer's suggestion
Changes in v2:
  - Fix compiling issue reported by sparse

 net/bluetooth/hci_event.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 2ad7b9f86f74..ef8c3bed7361 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -750,9 +750,23 @@ static u8 hci_cc_read_enc_key_size(struct hci_dev *hdev, void *data,
 	} else {
 		conn->enc_key_size = rp->key_size;
 		status = 0;
+
+		if (conn->enc_key_size < hdev->min_enc_key_size) {
+			/* As slave role, the conn->state has been set to
+			 * BT_CONNECTED and l2cap conn req might not be received
+			 * yet, at this moment the l2cap layer almost does
+			 * nothing with the non-zero status.
+			 * So we also clear encrypt related bits, and then the
+			 * handler of l2cap conn req will get the right secure
+			 * state at a later time.
+			 */
+			status = HCI_ERROR_AUTH_FAILURE;
+			clear_bit(HCI_CONN_ENCRYPT, &conn->flags);
+			clear_bit(HCI_CONN_AES_CCM, &conn->flags);
+		}
 	}
 
-	hci_encrypt_cfm(conn, 0);
+	hci_encrypt_cfm(conn, status);
 
 done:
 	hci_dev_unlock(hdev);
-- 
2.39.2

RE: [v3] Bluetooth: Add more enc key size check

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 2094 bytes --]

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=809021

---Test result---

Test Summary:
CheckPatch                    PASS      0.66 seconds
GitLint                       PASS      0.34 seconds
SubjectPrefix                 PASS      0.13 seconds
BuildKernel                   PASS      27.61 seconds
CheckAllWarning               PASS      30.37 seconds
CheckSparse                   WARNING   36.53 seconds
CheckSmatch                   WARNING   98.92 seconds
BuildKernel32                 PASS      27.25 seconds
TestRunnerSetup               PASS      421.86 seconds
TestRunner_l2cap-tester       PASS      22.96 seconds
TestRunner_iso-tester         PASS      46.60 seconds
TestRunner_bnep-tester        PASS      7.02 seconds
TestRunner_mgmt-tester        FAIL      167.54 seconds
TestRunner_rfcomm-tester      PASS      11.14 seconds
TestRunner_sco-tester         PASS      14.67 seconds
TestRunner_ioctl-tester       PASS      12.00 seconds
TestRunner_mesh-tester        PASS      8.92 seconds
TestRunner_smp-tester         PASS      9.93 seconds
TestRunner_userchan-tester    PASS      7.33 seconds
IncrementalBuild              PASS      26.08 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
Pairing Acceptor - SMP over BR/EDR 1                 Timed out    1.996 seconds


---
Regards,
Linux Bluetooth

Re: [PATCH v3] Bluetooth: Add more enc key size check

[patchwork-bot+bluetooth]

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Tue, 12 Dec 2023 10:30:34 +0800 you wrote:
> From: Alex Lu <alex_lu@realsil.com.cn>
> 
> When we are slave role and receives l2cap conn req when encryption has
> started, we should check the enc key size to avoid KNOB attack or BLUFFS
> attack.
> From SIG recommendation, implementations are advised to reject
> service-level connections on an encrypted baseband link with key
> strengths below 7 octets.
> A simple and clear way to achieve this is to place the enc key size
> check in hci_cc_read_enc_key_size()
> 
> [...]

Here is the summary with links:
  - [v3] Bluetooth: Add more enc key size check
    https://git.kernel.org/bluetooth/bluetooth-next/c/19921189d442

You are awesome, thank you!
-- 
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