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[109.252.18.135]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-37d240e95a3sm10648461fa.34.2025.11.28.06.45.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Nov 2025 06:45:20 -0800 (PST) From: Nazar Kalashnikov To: stable@vger.kernel.org, Greg Kroah-Hartman Cc: Nazar Kalashnikov , Marcel Holtmann , Johan Hedberg , "David S. Miller" , Jakub Kicinski , linux-bluetooth@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, lvc-project@linuxtesting.org, Alex Lu , Max Chou , Luiz Augusto von Dentz Subject: [PATCH 5.10/5.15] Bluetooth: Add more enc key size check Date: Fri, 28 Nov 2025 17:45:34 +0300 Message-ID: <20251128144535.55357-1-sivartiwe@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-bluetooth@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Alex Lu [ Upstream commit 04a342cc49a8522e99c9b3346371c329d841dcd2 ] 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 Signed-off-by: Max Chou Signed-off-by: Luiz Augusto von Dentz [ Nazar Kalashnikov: change status to rp_status due to function parameter conflict ] Signed-off-by: Nazar Kalashnikov --- Backport fix for CVE-2023-24023 net/bluetooth/hci_event.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c index c6dbb4aebfbc..6310f4f9890e 100644 --- a/net/bluetooth/hci_event.c +++ b/net/bluetooth/hci_event.c @@ -3043,6 +3043,7 @@ 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; BT_DBG("%s status 0x%02x", hdev->name, status); @@ -3052,6 +3053,7 @@ static void read_enc_key_size_complete(struct hci_dev *hdev, u8 status, } rp = (void *)skb->data; + rp_status = rp->status; handle = le16_to_cpu(rp->handle); hci_dev_lock(hdev); @@ -3064,15 +3066,30 @@ static void read_enc_key_size_complete(struct hci_dev *hdev, u8 status, * secure approach is to then assume the key size is 0 to force a * disconnection. */ - if (rp->status) { + if (rp_status) { bt_dev_err(hdev, "failed to read key size for handle %u", handle); conn->enc_key_size = 0; } 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); -- 2.43.0