diff mbox series

[SRU,Focal,1/1] Bluetooth: Add more enc key size check

Message ID 20240314102002.22662-2-yuxuan.luo@canonical.com
State New
Headers show
Series CVE-2023-24023 | expand

Commit Message

Yuxuan Luo March 14, 2024, 10:20 a.m. UTC 
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)

Cc: stable@vger.kernel.org
Signed-off-by: Alex Lu <alex_lu@realsil.com.cn>
Signed-off-by: Max Chou <max.chou@realtek.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
(backported from commit 04a342cc49a8522e99c9b3346371c329d841dcd2)
Signed-off-by: Yuxuan Luo <yuxuan.luo@canonical.com>
---
 net/bluetooth/hci_event.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index f5b46ea9d4c4d..3f3b14ce31eea 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -2902,6 +2902,7 @@  static void read_enc_key_size_complete(struct hci_dev *hdev, u8 status,
 	const struct hci_rp_read_enc_key_size *rp;
 	struct hci_conn *conn;
 	u16 handle;
+	u8 rp_status = rp->status;
 
 	BT_DBG("%s status 0x%02x", hdev->name, status);
 
@@ -2923,15 +2924,30 @@  static void read_enc_key_size_complete(struct hci_dev *hdev, u8 status,
 	 * (which is the same we do also when this HCI command isn't
 	 * supported.
 	 */
-	if (rp->status) {
+	if (rp_status) {
 		bt_dev_err(hdev, "failed to read key size for handle %u",
 			   handle);
 		conn->enc_key_size = HCI_LINK_KEY_SIZE;
 	} else {
 		conn->enc_key_size = rp->key_size;
+		rp_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.
+			 */
+			rp_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, rp_status);
 
 unlock:
 	hci_dev_unlock(hdev);