Bluetooth: hci_ldisc: Initialize hci_dev before open()

The hci_dev struct hdev is referenced in work queues and timers started
by open() in some protocols. This creates a race between the
initialization function and the work or timer which can result hdev
being dereferenced while it is still null.

The syzbot report contains a reliable reproducer which causes a null
pointer dereference of hdev in hci_uart_write_work() by making the
memory allocation for hdev fail.

To fix this, ensure hdev is valid from before calling a protocol's
open() until after calling a protocol's close().

Reported-by: syzbot+257790c15bcdef6fe00c@syzkaller.appspotmail.com
Signed-off-by: Jeremy Cline <jcline@redhat.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 14 insertions, 7 deletions

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index fbf7b4df23ab..4918fefc4a6f 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -207,11 +207,11 @@ void hci_uart_init_work(struct work_struct *work)
         err = hci_register_dev(hu->hdev);
         if (err < 0) {
                 BT_ERR("Can't register HCI device");
+                clear_bit(HCI_UART_PROTO_READY, &hu->flags);
+                hu->proto->close(hu);
                 hdev = hu->hdev;
                 hu->hdev = NULL;
                 hci_free_dev(hdev);
-                clear_bit(HCI_UART_PROTO_READY, &hu->flags);
-                hu->proto->close(hu);
                 return;
         }
 
@@ -616,6 +616,7 @@ static void hci_uart_tty_receive(struct tty_struct *tty, const u8 *data,
 static int hci_uart_register_dev(struct hci_uart *hu)
 {
         struct hci_dev *hdev;
+        int err;
 
         BT_DBG("");
 
@@ -659,11 +660,22 @@ static int hci_uart_register_dev(struct hci_uart *hu)
         else
                 hdev->dev_type = HCI_PRIMARY;
 
+        /* Only call open() for the protocol after hdev is fully initialized as
+         * open() (or a timer/workqueue it starts) may attempt to reference it.
+         */
+        err = hu->proto->open(hu);
+        if (err) {
+                hu->hdev = NULL;
+                hci_free_dev(hdev);
+                return err;
+        }
+
         if (test_bit(HCI_UART_INIT_PENDING, &hu->hdev_flags))
                 return 0;
 
         if (hci_register_dev(hdev) < 0) {
                 BT_ERR("Can't register HCI device");
+                hu->proto->close(hu);
                 hu->hdev = NULL;
                 hci_free_dev(hdev);
                 return -ENODEV;
@@ -683,17 +695,12 @@ static int hci_uart_set_proto(struct hci_uart *hu, int id)
         if (!p)
                 return -EPROTONOSUPPORT;
 
-        err = p->open(hu);
-        if (err)
-                return err;
-
         hu->proto = p;
         set_bit(HCI_UART_PROTO_READY, &hu->flags);
 
         err = hci_uart_register_dev(hu);
         if (err) {
                 clear_bit(HCI_UART_PROTO_READY, &hu->flags);
-                p->close(hu);
                 return err;
         }