[Bluetooth] Enforce security for outgoing RFCOMM connections

Recent tests with various Bluetooth headsets have shown that some of
them don't enforce authentication and encryption when connecting. All
of them leave it up to the host stack to enforce it. Non of them should
allow unencrypted connections, but that is how it is. So in case the
link mode settings require authentication and/or encryption it will now
also be enforced on outgoing RFCOMM connections. Previously this was
only done for incoming connections.

This support has a small drawback from a protocol level point of view
since the host stack can't really tell with 100% certainty if a remote
side is already authenticated or not. So if both sides are configured
to enforce authentication it will be requested twice. Most Bluetooth
chips are caching this information and thus no extra authentication
procedure has to be triggered over-the-air, but it can happen.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/rfcomm.h

@@ -181,6 +181,7 @@ struct rfcomm_dlc {
 	u8            priority;
 	u8            v24_sig;
 	u8            mscex;
+	u8            out;
 
 	u32           link_mode;
 

net/bluetooth/rfcomm/core.c

@@ -53,7 +53,7 @@
 #define BT_DBG(D...)
 #endif
 
-#define VERSION "1.8"
+#define VERSION "1.9"
 
 static int disable_cfc = 0;
 static int channel_mtu = -1;
@@ -230,6 +230,21 @@ static int rfcomm_l2sock_create(struct socket **sock)
 	return err;
 }
 
+static inline int rfcomm_check_link_mode(struct rfcomm_dlc *d)
+{
+	struct sock *sk = d->session->sock->sk;
+
+	if (d->link_mode & (RFCOMM_LM_ENCRYPT | RFCOMM_LM_SECURE)) {
+		if (!hci_conn_encrypt(l2cap_pi(sk)->conn->hcon))
+			return 1;
+	} else if (d->link_mode & RFCOMM_LM_AUTH) {
+		if (!hci_conn_auth(l2cap_pi(sk)->conn->hcon))
+			return 1;
+	}
+
+	return 0;
+}
+
 /* ---- RFCOMM DLCs ---- */
 static void rfcomm_dlc_timeout(unsigned long arg)
 {
@@ -371,15 +386,23 @@ static int __rfcomm_dlc_open(struct rfcomm_dlc *d, bdaddr_t *src, bdaddr_t *dst,
 	d->addr     = __addr(s->initiator, dlci);
 	d->priority = 7;
 
-	d->state    = BT_CONFIG;
+	d->state = BT_CONFIG;
 	rfcomm_dlc_link(s, d);
 
+	d->out = 1;
+
 	d->mtu = s->mtu;
 	d->cfc = (s->cfc == RFCOMM_CFC_UNKNOWN) ? 0 : s->cfc;
 
-	if (s->state == BT_CONNECTED)
-		rfcomm_send_pn(s, 1, d);
+	if (s->state == BT_CONNECTED) {
+		if (rfcomm_check_link_mode(d))
+			set_bit(RFCOMM_AUTH_PENDING, &d->flags);
+		else
+			rfcomm_send_pn(s, 1, d);
+	}
+
 	rfcomm_dlc_set_timer(d, RFCOMM_CONN_TIMEOUT);
+
 	return 0;
 }
 
@@ -1146,21 +1169,6 @@ static int rfcomm_recv_disc(struct rfcomm_session *s, u8 dlci)
 	return 0;
 }
 
-static inline int rfcomm_check_link_mode(struct rfcomm_dlc *d)
-{
-	struct sock *sk = d->session->sock->sk;
-
-	if (d->link_mode & (RFCOMM_LM_ENCRYPT | RFCOMM_LM_SECURE)) {
-		if (!hci_conn_encrypt(l2cap_pi(sk)->conn->hcon))
-			return 1;
-	} else if (d->link_mode & RFCOMM_LM_AUTH) {
-		if (!hci_conn_auth(l2cap_pi(sk)->conn->hcon))
-			return 1;
-	}
-
-	return 0;
-}
-
 static void rfcomm_dlc_accept(struct rfcomm_dlc *d)
 {
 	struct sock *sk = d->session->sock->sk;
@@ -1205,10 +1213,8 @@ static int rfcomm_recv_sabm(struct rfcomm_session *s, u8 dlci)
 			if (rfcomm_check_link_mode(d)) {
 				set_bit(RFCOMM_AUTH_PENDING, &d->flags);
 				rfcomm_dlc_set_timer(d, RFCOMM_AUTH_TIMEOUT);
-				return 0;
-			}
-
-			rfcomm_dlc_accept(d);
+			} else
+				rfcomm_dlc_accept(d);
 		}
 		return 0;
 	}
@@ -1223,10 +1229,8 @@ static int rfcomm_recv_sabm(struct rfcomm_session *s, u8 dlci)
 		if (rfcomm_check_link_mode(d)) {
 			set_bit(RFCOMM_AUTH_PENDING, &d->flags);
 			rfcomm_dlc_set_timer(d, RFCOMM_AUTH_TIMEOUT);
-			return 0;
-		}
-
-		rfcomm_dlc_accept(d);
+		} else
+			rfcomm_dlc_accept(d);
 	} else {
 		rfcomm_send_dm(s, dlci);
 	}
@@ -1636,7 +1640,11 @@ static void rfcomm_process_connect(struct rfcomm_session *s)
 		d = list_entry(p, struct rfcomm_dlc, list);
 		if (d->state == BT_CONFIG) {
 			d->mtu = s->mtu;
-			rfcomm_send_pn(s, 1, d);
+			if (rfcomm_check_link_mode(d)) {
+				set_bit(RFCOMM_AUTH_PENDING, &d->flags);
+				rfcomm_dlc_set_timer(d, RFCOMM_AUTH_TIMEOUT);
+			} else
+				rfcomm_send_pn(s, 1, d);
 		}
 	}
 }
@@ -1709,7 +1717,11 @@ static inline void rfcomm_process_dlcs(struct rfcomm_session *s)
 
 		if (test_and_clear_bit(RFCOMM_AUTH_ACCEPT, &d->flags)) {
 			rfcomm_dlc_clear_timer(d);
-			rfcomm_dlc_accept(d);
+			if (d->out) {
+				rfcomm_send_pn(s, 1, d);
+				rfcomm_dlc_set_timer(d, RFCOMM_CONN_TIMEOUT);
+			} else
+				rfcomm_dlc_accept(d);
 			if (d->link_mode & RFCOMM_LM_SECURE) {
 				struct sock *sk = s->sock->sk;
 				hci_conn_change_link_key(l2cap_pi(sk)->conn->hcon);
@@ -1717,7 +1729,10 @@ static inline void rfcomm_process_dlcs(struct rfcomm_session *s)
 			continue;
 		} else if (test_and_clear_bit(RFCOMM_AUTH_REJECT, &d->flags)) {
 			rfcomm_dlc_clear_timer(d);
-			rfcomm_send_dm(s, d->dlci);
+			if (!d->out)
+				rfcomm_send_dm(s, d->dlci);
+			else
+				d->state = BT_CLOSED;
 			__rfcomm_dlc_close(d, ECONNREFUSED);
 			continue;
 		}
@@ -1726,7 +1741,7 @@ static inline void rfcomm_process_dlcs(struct rfcomm_session *s)
 			continue;
 
 		if ((d->state == BT_CONNECTED || d->state == BT_DISCONN) &&
-				d->mscex == RFCOMM_MSCEX_OK)
+						d->mscex == RFCOMM_MSCEX_OK)
 			rfcomm_process_tx(d);
 	}
 }

net/bluetooth/rfcomm/sock.c

@@ -309,13 +309,13 @@ static struct sock *rfcomm_sock_alloc(struct net *net, struct socket *sock, int
 	sk->sk_destruct = rfcomm_sock_destruct;
 	sk->sk_sndtimeo = RFCOMM_CONN_TIMEOUT;
 
-	sk->sk_sndbuf   = RFCOMM_MAX_CREDITS * RFCOMM_DEFAULT_MTU * 10;
-	sk->sk_rcvbuf   = RFCOMM_MAX_CREDITS * RFCOMM_DEFAULT_MTU * 10;
+	sk->sk_sndbuf = RFCOMM_MAX_CREDITS * RFCOMM_DEFAULT_MTU * 10;
+	sk->sk_rcvbuf = RFCOMM_MAX_CREDITS * RFCOMM_DEFAULT_MTU * 10;
 
 	sock_reset_flag(sk, SOCK_ZAPPED);
 
 	sk->sk_protocol = proto;
-	sk->sk_state	= BT_OPEN;
+	sk->sk_state    = BT_OPEN;
 
 	bt_sock_link(&rfcomm_sk_list, sk);
 
@@ -413,6 +413,8 @@ static int rfcomm_sock_connect(struct socket *sock, struct sockaddr *addr, int a
 	bacpy(&bt_sk(sk)->dst, &sa->rc_bdaddr);
 	rfcomm_pi(sk)->channel = sa->rc_channel;
 
+	d->link_mode = rfcomm_pi(sk)->link_mode;
+
 	err = rfcomm_dlc_open(d, &bt_sk(sk)->src, &sa->rc_bdaddr, sa->rc_channel);
 	if (!err)
 		err = bt_sock_wait_state(sk, BT_CONNECTED,