From patchwork Tue Dec 12 02:30:34 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alex Lu X-Patchwork-Id: 13488406 Received: from rtits2.realtek.com.tw (rtits2.realtek.com [211.75.126.72]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A44358E; Mon, 11 Dec 2023 18:38:42 -0800 (PST) X-SpamFilter-By: ArmorX SpamTrap 5.78 with qID 3BC2Uhc763147471, This message is accepted by code: ctloc85258 Received: from RSEXMBS01.realsil.com.cn ([172.29.17.195]) by rtits2.realtek.com.tw (8.15.2/2.95/5.92) with ESMTPS id 3BC2Uhc763147471 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=FAIL); Tue, 12 Dec 2023 10:30:45 +0800 Received: from alexlu (172.29.36.158) by RSEXMBS01.realsil.com.cn (172.29.17.195) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.27; Tue, 12 Dec 2023 10:30:43 +0800 Date: Tue, 12 Dec 2023 10:30:34 +0800 From: Alex Lu To: Marcel Holtmann , Johan Hedberg , Luiz Augusto von Dentz , , CC: Max Chou , Karen Hsu Subject: [PATCH v3] Bluetooth: Add more enc key size check Message-ID: Precedence: bulk X-Mailing-List: linux-bluetooth@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline X-ClientProxiedBy: RSEXH36502.realsil.com.cn (172.29.17.3) To RSEXMBS01.realsil.com.cn (172.29.17.195) From: Alex Lu 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 Signed-off-by: Max Chou --- 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);