Bluetooth: Verify dlci not in use before rfcomm_dev create

Only one session/channel combination may be in use at any one
time. However, the failure does not occur until the tty is
opened (in rfcomm_dlc_open()).

Because these settings are actually bound at rfcomm device
creation (via RFCOMMCREATEDEV ioctl), validate and fail before
creating the rfcomm tty device.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Tested-By: Alexander Holler <holler@ahsoftware.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/rfcomm.h

@@ -241,6 +241,7 @@ int  rfcomm_dlc_send(struct rfcomm_dlc *d, struct sk_buff *skb);
 int  rfcomm_dlc_set_modem_status(struct rfcomm_dlc *d, u8 v24_sig);
 int  rfcomm_dlc_get_modem_status(struct rfcomm_dlc *d, u8 *v24_sig);
 void rfcomm_dlc_accept(struct rfcomm_dlc *d);
+struct rfcomm_dlc *rfcomm_dlc_exists(bdaddr_t *src, bdaddr_t *dst, u8 channel);
 
 #define rfcomm_dlc_lock(d)     spin_lock(&d->lock)
 #define rfcomm_dlc_unlock(d)   spin_unlock(&d->lock)

net/bluetooth/rfcomm/core.c

@@ -360,6 +360,11 @@ static struct rfcomm_dlc *rfcomm_dlc_get(struct rfcomm_session *s, u8 dlci)
 	return NULL;
 }
 
+static int rfcomm_check_channel(u8 channel)
+{
+	return channel < 1 || channel > 30;
+}
+
 static int __rfcomm_dlc_open(struct rfcomm_dlc *d, bdaddr_t *src, bdaddr_t *dst, u8 channel)
 {
 	struct rfcomm_session *s;
@@ -369,7 +374,7 @@ static int __rfcomm_dlc_open(struct rfcomm_dlc *d, bdaddr_t *src, bdaddr_t *dst,
 	BT_DBG("dlc %p state %ld %pMR -> %pMR channel %d",
 	       d, d->state, src, dst, channel);
 
-	if (channel < 1 || channel > 30)
+	if (rfcomm_check_channel(channel))
 		return -EINVAL;
 
 	if (d->state != BT_OPEN && d->state != BT_CLOSED)
@@ -514,6 +519,25 @@ int rfcomm_dlc_close(struct rfcomm_dlc *d, int err)
 	return r;
 }
 
+struct rfcomm_dlc *rfcomm_dlc_exists(bdaddr_t *src, bdaddr_t *dst, u8 channel)
+{
+	struct rfcomm_session *s;
+	struct rfcomm_dlc *dlc = NULL;
+	u8 dlci;
+
+	if (rfcomm_check_channel(channel))
+		return ERR_PTR(-EINVAL);
+
+	rfcomm_lock();
+	s = rfcomm_session_get(src, dst);
+	if (s) {
+		dlci = __dlci(!s->initiator, channel);
+		dlc = rfcomm_dlc_get(s, dlci);
+	}
+	rfcomm_unlock();
+	return dlc;
+}
+
 int rfcomm_dlc_send(struct rfcomm_dlc *d, struct sk_buff *skb)
 {
 	int len = skb->len;

net/bluetooth/rfcomm/tty.c

@@ -385,6 +385,14 @@ static int rfcomm_create_dev(struct sock *sk, void __user *arg)
 		dlc = rfcomm_pi(sk)->dlc;
 		rfcomm_dlc_hold(dlc);
 	} else {
+		/* Validate the channel is unused */
+		dlc = rfcomm_dlc_exists(&req.src, &req.dst, req.channel);
+		if (IS_ERR(dlc))
+			return PTR_ERR(dlc);
+		else if (dlc) {
+			rfcomm_dlc_put(dlc);
+			return -EBUSY;
+		}
 		dlc = rfcomm_dlc_alloc(GFP_KERNEL);
 		if (!dlc)
 			return -ENOMEM;