linux-kernel - [PATCH v2] Bluetooth: Avoid redundant authentication

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Message-ID: <20230907043933.v2.1.I0cd65c6ecb991a13b224614c32c1946f9eecea3d@changeid>
Date:   Thu,  7 Sep 2023 04:39:34 +0000
From:   Ying Hsu <yinghsu@...omium.org>
To:     linux-bluetooth@...r.kernel.org, marcel@...tmann.org
Cc:     chromeos-bluetooth-upstreaming@...omium.org,
        Ying Hsu <yinghsu@...omium.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] Bluetooth: Avoid redundant authentication

While executing the Android 13 CTS Verifier Secure Server test on a
ChromeOS device, it was observed that the Bluetooth host initiates
authentication for an RFCOMM connection after SSP completes.
When this happens, some Intel Bluetooth controllers, like AC9560, would
disconnect with "Connection Rejected due to Security Reasons (0x0e)".

Historically, BlueZ did not mandate this authentication while an
authenticated combination key was already in use for the connection.
This behavior was changed since commit 7b5a9241b780
("Bluetooth: Introduce requirements for security level 4").
So, this patch addresses the aforementioned disconnection issue by
restoring the previous behavior.

Signed-off-by: Ying Hsu <yinghsu@...omium.org>
---
- Tested CTS Verifier 13 Secure Server test on a chromebook with AC9560.
- Manual tests on classic mouse/keyboard/headset, BLE keyboard/mouse.

Changes in v2:
- Transitioned from multiple 'if' blocks to a 'switch-case' structure
  for clarity and maintainability.

 net/bluetooth/hci_conn.c | 63 ++++++++++++++++++++++------------------
 1 file changed, 35 insertions(+), 28 deletions(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 9d5057cef30a..7a6f20338db8 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -2413,34 +2413,41 @@ int hci_conn_security(struct hci_conn *conn, __u8 sec_level, __u8 auth_type,
 	if (!test_bit(HCI_CONN_AUTH, &conn->flags))
 		goto auth;
 
-	/* An authenticated FIPS approved combination key has sufficient
-	 * security for security level 4. */
-	if (conn->key_type == HCI_LK_AUTH_COMBINATION_P256 &&
-	    sec_level == BT_SECURITY_FIPS)
-		goto encrypt;
-
-	/* An authenticated combination key has sufficient security for
-	   security level 3. */
-	if ((conn->key_type == HCI_LK_AUTH_COMBINATION_P192 ||
-	     conn->key_type == HCI_LK_AUTH_COMBINATION_P256) &&
-	    sec_level == BT_SECURITY_HIGH)
-		goto encrypt;
-
-	/* An unauthenticated combination key has sufficient security for
-	   security level 1 and 2. */
-	if ((conn->key_type == HCI_LK_UNAUTH_COMBINATION_P192 ||
-	     conn->key_type == HCI_LK_UNAUTH_COMBINATION_P256) &&
-	    (sec_level == BT_SECURITY_MEDIUM || sec_level == BT_SECURITY_LOW))
-		goto encrypt;
-
-	/* A combination key has always sufficient security for the security
-	   levels 1 or 2. High security level requires the combination key
-	   is generated using maximum PIN code length (16).
-	   For pre 2.1 units. */
-	if (conn->key_type == HCI_LK_COMBINATION &&
-	    (sec_level == BT_SECURITY_MEDIUM || sec_level == BT_SECURITY_LOW ||
-	     conn->pin_length == 16))
-		goto encrypt;
+	switch (conn->key_type) {
+	case HCI_LK_AUTH_COMBINATION_P256:
+		/* An authenticated FIPS approved combination key has
+		 * sufficient security for security level 4 or lower.
+		 */
+		if (sec_level <= BT_SECURITY_FIPS)
+			goto encrypt;
+		break;
+	case HCI_LK_AUTH_COMBINATION_P192:
+		/* An authenticated combination key has sufficient security for
+		 * security level 3 or lower.
+		 */
+		if (sec_level <= BT_SECURITY_HIGH)
+			goto encrypt;
+		break;
+	case HCI_LK_UNAUTH_COMBINATION_P192:
+	case HCI_LK_UNAUTH_COMBINATION_P256:
+		/* An unauthenticated combination key has sufficient security
+		 * for security level 2 or lower.
+		 */
+		if (sec_level <= BT_SECURITY_MEDIUM)
+			goto encrypt;
+		break;
+	case HCI_LK_COMBINATION:
+		/* A combination key has always sufficient security for the
+		 * security levels 2 or lower. High security level requires the
+		 * combination key is generated using maximum PIN code length
+		 * (16). For pre 2.1 units.
+		 */
+		if (sec_level <= BT_SECURITY_MEDIUM || conn->pin_length == 16)
+			goto encrypt;
+		break;
+	default:
+		break;
+	}
 
 auth:
 	if (test_bit(HCI_CONN_ENCRYPT_PEND, &conn->flags))
-- 
2.42.0.283.g2d96d420d3-goog