Bluetooth: Pause RFCOMM TX when encryption drops

A role switch with devices following the Bluetooth pre-2.1 standards
or without Encryption Pause and Resume support is not possible if
encryption is enabled. Most newer headsets require the role switch,
but also require that the connection is encrypted.

For connections with a high security mode setting, the link will be
immediately dropped. When the connection uses medium security mode
setting, then a grace period is introduced where the TX is halted and
the remote device gets a change to re-enable encryption after the
role switch. If not re-enabled the link will be dropped.

Based on initial work by Ville Tervo <ville.tervo@nokia.com>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/rfcomm.h

@@ -204,10 +204,11 @@ struct rfcomm_dlc {
 #define RFCOMM_TX_THROTTLED 1
 #define RFCOMM_TIMED_OUT    2
 #define RFCOMM_MSC_PENDING  3
-#define RFCOMM_AUTH_PENDING 4
-#define RFCOMM_AUTH_ACCEPT  5
-#define RFCOMM_AUTH_REJECT  6
-#define RFCOMM_DEFER_SETUP  7
+#define RFCOMM_SEC_PENDING  4
+#define RFCOMM_AUTH_PENDING 5
+#define RFCOMM_AUTH_ACCEPT  6
+#define RFCOMM_AUTH_REJECT  7
+#define RFCOMM_DEFER_SETUP  8
 
 /* Scheduling flags and events */
 #define RFCOMM_SCHED_STATE  0

net/bluetooth/rfcomm/core.c

@@ -1979,12 +1979,23 @@ static void rfcomm_security_cfm(struct hci_conn *conn, u8 status, u8 encrypt)
 	list_for_each_safe(p, n, &s->dlcs) {
 		d = list_entry(p, struct rfcomm_dlc, list);
 
-		if (!status && encrypt == 0x00 &&
-				d->sec_level == BT_SECURITY_HIGH &&
-					(d->state == BT_CONNECTED ||
-						d->state == BT_CONFIG)) {
-			__rfcomm_dlc_close(d, ECONNREFUSED);
-			continue;
+		if (test_and_clear_bit(RFCOMM_SEC_PENDING, &d->flags)) {
+			rfcomm_dlc_clear_timer(d);
+			if (status || encrypt == 0x00) {
+				__rfcomm_dlc_close(d, ECONNREFUSED);
+				continue;
+			}
+		}
+
+		if (d->state == BT_CONNECTED && !status && encrypt == 0x00) {
+			if (d->sec_level == BT_SECURITY_MEDIUM) {
+				set_bit(RFCOMM_SEC_PENDING, &d->flags);
+				rfcomm_dlc_set_timer(d, RFCOMM_AUTH_TIMEOUT);
+				continue;
+			} else if (d->sec_level == BT_SECURITY_HIGH) {
+				__rfcomm_dlc_close(d, ECONNREFUSED);
+				continue;
+			}
 		}
 
 		if (!test_and_clear_bit(RFCOMM_AUTH_PENDING, &d->flags))