Bluetooth: hci_uart: Fix NULL deref in recv callbacks when priv is uninitialized

When a fault is injected during hci_uart line discipline setup, the
proto open() callback may fail leaving hu->priv as NULL. A subsequent
TIOCSTI ioctl can trigger the recv() callback before priv is
initialized, causing a NULL pointer dereference.

Fix all four affected HCI UART protocol drivers by adding a NULL check
on hu->priv at the start of their recv() callbacks: h4, h5, ath and
bcsp.

Reported-by: syzbot+ff30eeab8e07b37d524e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ff30eeab8e07b37d524e
Signed-off-by: Aurelien DESBRIERES <aurelien@hackers.camp>
Assisted-by: Claude:claude-sonnet-4-6
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

drivers/bluetooth/hci_ath.c

@@ -191,6 +191,9 @@ static int ath_recv(struct hci_uart *hu, const void *data, int count)
 {
 	struct ath_struct *ath = hu->priv;
 
+	if (!ath)
+		return -ENODEV;
+
 	ath->rx_skb = h4_recv_buf(hu, ath->rx_skb, data, count,
 				  ath_recv_pkts, ARRAY_SIZE(ath_recv_pkts));
 	if (IS_ERR(ath->rx_skb)) {

drivers/bluetooth/hci_bcsp.c

@@ -585,6 +585,9 @@ static int bcsp_recv(struct hci_uart *hu, const void *data, int count)
 	if (!test_bit(HCI_UART_REGISTERED, &hu->flags))
 		return -EUNATCH;
 
+	if (!bcsp)
+		return -ENODEV;
+
 	BT_DBG("hu %p count %d rx_state %d rx_count %ld",
 	       hu, count, bcsp->rx_state, bcsp->rx_count);
 

drivers/bluetooth/hci_h4.c

@@ -109,6 +109,9 @@ static int h4_recv(struct hci_uart *hu, const void *data, int count)
 {
 	struct h4_struct *h4 = hu->priv;
 
+	if (!h4)
+		return -ENODEV;
+
 	h4->rx_skb = h4_recv_buf(hu, h4->rx_skb, data, count,
 				 h4_recv_pkts, ARRAY_SIZE(h4_recv_pkts));
 	if (IS_ERR(h4->rx_skb)) {

drivers/bluetooth/hci_h5.c

@@ -587,6 +587,9 @@ static int h5_recv(struct hci_uart *hu, const void *data, int count)
 	struct h5 *h5 = hu->priv;
 	const unsigned char *ptr = data;
 
+	if (!h5)
+		return -ENODEV;
+
 	BT_DBG("%s pending %zu count %d", hu->hdev->name, h5->rx_pending,
 	       count);