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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Wed, 12 Feb 2020 13:29:45 -0800
Message-ID: <CABBYNZLm_q_WV3nmGVpePXpLsjnkk_zpEm1cYK0ps7H3PM=_kQ@mail.gmail.com>
Subject: Re: [Bluez PATCH v3] bluetooth: secure bluetooth stack from bluedump attack
To:     Johan Hedberg <johan.hedberg@gmail.com>
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        Howard Chung <howardchung@google.com>,
        Bluez mailing list <linux-bluetooth@vger.kernel.org>,
        ChromeOS Bluetooth Upstreaming 
        <chromeos-bluetooth-upstreaming@chromium.org>,
        "David S. Miller" <davem@davemloft.net>,
        "open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Howard,

On Wed, Feb 12, 2020 at 7:39 AM Johan Hedberg <johan.hedberg@gmail.com> wrote:
>
> Hi Marcel,
>
> On 12. Feb 2020, at 17.19, Marcel Holtmann <marcel@holtmann.org> wrote:
> >> +            key = hci_find_ltk(hcon->hdev, &hcon->dst, hcon->dst_type,
> >> +                               hcon->role);
> >> +
> >> +            /* If there already exists link key in local host, leave the
> >> +             * decision to user space since the remote device could be
> >> +             * legitimate or malicious.
> >> +             */
> >> +            if (smp->method == JUST_WORKS && key) {
> >> +                    err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
> >> +                                                    hcon->type,
> >> +                                                    hcon->dst_type, passkey,
> >> +                                                    1);
> >> +                    if (err)
> >> +                            return SMP_UNSPECIFIED;
> >> +                    set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
> >> +            }
> >>      }
> >
> > while this looks good, I like to optimize this to only look up the LTK when needed.

I wonder why we don't just call user confirm everytime? That way the
new policy preference applies to both a new pair or when already
paired, and we don't have to really do the key lookup here since the
userspace can do the check if really needed.

> >
> >       /* comment here */
> >       if (smp->method != JUST_WORKS)
> >               goto mackey_and_ltk;
> >
> >
> >       /* and command here */
> >       if (hci_find_ltk()) {
> >               mgmt_user_confirm_request()
> >               ..
> >       }
> >
> > And my preference that we also get an Ack from Johan or Luiz that double checked that this is fine.
>
> Acked-by: Johan Hedberg <johan.hedberg@intel.com>
>
> Johan


-- 
Luiz Augusto von Dentz