[PATCH] Bluetooth: Fix use-after-free read in hci_cmd_timeout()

[Shigeru Yoshida <syoshida@xxxxxxxxxx>]

syzbot reported use-after-free in hci_cmd_timeout() [1].  The scenario
for the issue is as follows:

Task                                    Workqueue
----------------------------------------------------------------------
hci_dev_open_sync
  ...
  hci_dev_init_sync  <- failed
  ...
  if (hdev->sent_cmd)
    kfree_skb(hdev->sent_cmd)
                                        hci_cmd_timeout
                                          ...
                                          if (hdev->sent_cmd)
                                            sent = hdev->sent_cmd->data
                                                   ^^ UAF occurred
    hdev->sent_cmd = NULL

When hci_dev_init_sync() failed, hci_dev_open_sync() frees
hdev->send_cmd and set it to NULL.  However, hci_cmd_timeout() can run
just after freeing hdev->sent_cmd because hdev->cmd_timer is not
canceled.

This patch fixes the issue by canceling hdev->cmd_timer before freeing
hdev->sent_cmd.

Link: https://syzkaller.appspot.com/bug?id=cb23ebfc8f304f510fb717cb783fe8b496c7ffb1 [1]
Reported-by: syzbot+19a9f729f05272857487@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
---
 net/bluetooth/hci_sync.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index 76c3107c9f91..a011065220e4 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -4696,6 +4696,7 @@ int hci_dev_open_sync(struct hci_dev *hdev)
 			hdev->flush(hdev);
 
 		if (hdev->sent_cmd) {
+			cancel_delayed_work_sync(&hdev->cmd_timer);
 			kfree_skb(hdev->sent_cmd);
 			hdev->sent_cmd = NULL;
 		}
-- 
2.38.1