Re: [PATCH] Bluetooth: reorganize ioctls from hci_sock_bound_ioctl()

Hi Tetsuo,

On Wed, Jul 21, 2021 at 4:42 PM Tetsuo Handa
[off-list ref] wrote:

On 2021/07/22 3:17, Luiz Augusto von Dentz wrote:

quoted

I think it would have been cleaner if we have dedicated functions for
each command like I did in my patch:

https://patchwork.kernel.org/project/bluetooth/patch/20210717000731.3836303-1-luiz.dentz@gmail.com/

But your patch was proven to be unsafe. There is a use-after-unregister
race window which would require at least 1000 lines of modification and
a lot of careful review if we try to manage without my patch.
Such all-in-one-step change is too much for "sleep in atomic context"
regression fix which is preventing syzbot from testing Bluetooth module
and is preventing Linux distributors from fixing CVE-2021-3573.

Im not saying you should adopt my solution, the locking etc stay the
same as in this set but each command should have a helper function to
make it clearer that way we don't have to re-evaluate the command over
and over.

As far as I can see, it is lock_sock() (not bh_lock_sock_nested() in your
patch) that is needed for protecting

        sk->sk_err = EPIPE;
        sk->sk_state = BT_OPEN;
        sk->sk_state_change(sk);

in hci_sock_dev_event(HCI_DEV_UNREG) from concurrent modification

        lock_sock(sk);

        if (sk->sk_state == BT_BOUND) {
                err = -EALREADY;
                goto done;
        }

        (...snipped...)

-               hci_pi(sk)->hdev = hdev;
+               if (hdev) {
+                       hci_pi(sk)->dev = hdev->id;
+                       hci_dev_put(hdev);
+               }

        (...snipped...)
        /* Race window is here. */
        (...snipped...)

        sk->sk_state = BT_BOUND;
done:
        release_sock(sk);

in hci_sock_bind().

quoted

That way it is simpler to protect the likes of
copy_from_user/copy_to_user, etc, even if we have to some checks
duplicated on each function we can have a helper function to checks
the flags, etc.

My patch calls copy_from_user()/copy_to_user() without lock_sock()
which works nicely with "[PATCH v3] Bluetooth: call lock_sock() outside
of spinlock section". I'd like to backport "[PATCH v2] Bluetooth:
reorganize ioctls from hci_sock_bound_ioctl()" together.

Yep, Im not asking you to change any of that.


-- 
Luiz Augusto von Dentz