[Bluetooth] Reject L2CAP connections on an insecure ACL link

The Security Mode 4 of the Bluetooth 2.1 specification has strict
authentication and encryption requirements. It is the initiators job
to create a secure ACL link. However in case of malicious devices, the
acceptor has to make sure that the ACL is encrypted before allowing
any kind of L2CAP connection. The only exception here is the PSM 1 for
the service discovery protocol, because that is allowed to run on an
insecure ACL link.

Previously it was enough to reject a L2CAP connection during the
connection setup phase, but with Bluetooth 2.1 it is forbidden to
do any L2CAP protocol exchange on an insecure link (except SDP).

The new hci_conn_check_link_mode() function can be used to check the
integrity of an ACL link. This functions also takes care of the cases
where Security Mode 4 is disabled or one of the devices is based on
an older specification.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

3 files changed, 25 insertions, 5 deletions

diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
index 1edfdf4..f6348e0 100644
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -49,7 +49,7 @@
 #define BT_DBG(D...)
 #endif
 
-#define VERSION "2.12"
+#define VERSION "2.13"
 
 /* Bluetooth sockets */
 #define BT_MAX_PROTO	8
diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index a2f9efa..b700242 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -376,6 +376,19 @@ struct hci_conn *hci_connect(struct hci_dev *hdev, int type, bdaddr_t *dst, __u8
 }
 EXPORT_SYMBOL(hci_connect);
 
+/* Check link security requirement */
+int hci_conn_check_link_mode(struct hci_conn *conn)
+{
+	BT_DBG("conn %p", conn);
+
+	if (conn->ssp_mode > 0 && conn->hdev->ssp_mode > 0 &&
+					!(conn->link_mode & HCI_LM_ENCRYPT))
+		return 0;
+
+	return 1;
+}
+EXPORT_SYMBOL(hci_conn_check_link_mode);
+
 /* Authenticate remote device */
 int hci_conn_auth(struct hci_conn *conn)
 {
diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index a96d6de..9610a9c 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -1568,10 +1568,10 @@ static inline int l2cap_connect_req(struct l2cap_conn *conn, struct l2cap_cmd_hd
 	struct l2cap_conn_req *req = (struct l2cap_conn_req *) data;
 	struct l2cap_conn_rsp rsp;
 	struct sock *sk, *parent;
-	int result, status = 0;
+	int result, status = L2CAP_CS_NO_INFO;
 
 	u16 dcid = 0, scid = __le16_to_cpu(req->scid);
-	__le16 psm  = req->psm;
+	__le16 psm = req->psm;
 
 	BT_DBG("psm 0x%2.2x scid 0x%4.4x", psm, scid);
 
@@ -1582,6 +1582,13 @@ static inline int l2cap_connect_req(struct l2cap_conn *conn, struct l2cap_cmd_hd
 		goto sendresp;
 	}
 
+	/* Check if the ACL is secure enough (if not SDP) */
+	if (psm != cpu_to_le16(0x0001) &&
+				!hci_conn_check_link_mode(conn->hcon)) {
+		result = L2CAP_CR_SEC_BLOCK;
+		goto response;
+	}
+
 	result = L2CAP_CR_NO_MEM;
 
 	/* Check for backlog size */
@@ -2239,7 +2246,7 @@ static int l2cap_auth_cfm(struct hci_conn *hcon, u8 status)
 			rsp.scid   = cpu_to_le16(l2cap_pi(sk)->dcid);
 			rsp.dcid   = cpu_to_le16(l2cap_pi(sk)->scid);
 			rsp.result = cpu_to_le16(result);
-			rsp.status = cpu_to_le16(0);
+			rsp.status = cpu_to_le16(L2CAP_CS_NO_INFO);
 			l2cap_send_cmd(conn, l2cap_pi(sk)->ident,
 					L2CAP_CONN_RSP, sizeof(rsp), &rsp);
 		}
@@ -2311,7 +2318,7 @@ static int l2cap_encrypt_cfm(struct hci_conn *hcon, u8 status, u8 encrypt)
 			rsp.scid   = cpu_to_le16(l2cap_pi(sk)->dcid);
 			rsp.dcid   = cpu_to_le16(l2cap_pi(sk)->scid);
 			rsp.result = cpu_to_le16(result);
-			rsp.status = cpu_to_le16(0);
+			rsp.status = cpu_to_le16(L2CAP_CS_NO_INFO);
 			l2cap_send_cmd(conn, l2cap_pi(sk)->ident,
 					L2CAP_CONN_RSP, sizeof(rsp), &rsp);
 		}