Bluetooth: hci_uart: Check if socket buffer is ERR_PTR in h4_recv_buf()

commit 1dc2d785 upstream.

h4_recv_buf() callers store the return value to socket buffer and
recursively pass the buffer to h4_recv_buf() without protection. So,
ERR_PTR returned from h4_recv_buf() can be dereferenced, if called again
before setting the socket buffer to NULL from previous error. Check if
skb is ERR_PTR in h4_recv_buf().

Reported-by: syzbot+017a32f149406df32703@syzkaller.appspotmail.com
Signed-off-by: Myungho Jung <mhjungk@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/bluetooth/hci_h4.c

@@ -174,6 +174,10 @@ struct sk_buff *h4_recv_buf(struct hci_dev *hdev, struct sk_buff *skb,
 	struct hci_uart *hu = hci_get_drvdata(hdev);
 	u8 alignment = hu->alignment ? hu->alignment : 1;
 
+	/* Check for error from previous call */
+	if (IS_ERR(skb))
+		skb = NULL;
+
 	while (count) {
 		int i, len;