netdev - Re: [RFC PATCH] Bluetooth: hci_event: Ignore multiple conn complete events

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Message-ID: <CABBYNZ+VQ3Gfw0n=PavFhnnOy2=+1OAeV5UT_S25Lz_4gWzWEQ@mail.gmail.com>
Date:   Fri, 21 Jan 2022 13:31:25 -0800
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     Sönke Huster <soenke.huster@...oes.de>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] Bluetooth: hci_event: Ignore multiple conn complete events

Hi Sönke,

On Fri, Jan 21, 2022 at 10:22 AM Sönke Huster <soenke.huster@...oes.de> wrote:
>
> I just noticed that just checking for handle does not work, as obviously 0x0 could also be a handle value and therefore it can't be distinguished, whether it is not set yet or it is 0x0.

Yep, we should probably check its state, check for state != BT_OPEN
since that is what hci_conn_add initialize the state.

> On 21.01.22 18:36, Soenke Huster wrote:
> > When a HCI_CONNECTION_COMPLETE event is received multiple times
> > for the same handle, the device is registered multiple times which leads
> > to memory corruptions. Therefore, consequent events for a single
> > connection are ignored.
> >
> > The conn->state can hold different values so conn->handle is
> > checked to detect whether a connection is already set up.
> >
> > Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=215497
> > Signed-off-by: Soenke Huster <soenke.huster@...oes.de>
> > ---
> > This fixes the referenced bug and several use-after-free issues I discovered.
> > I tagged it as RFC, as I am not 100% sure if checking the existence of the
> > handle is the correct approach, but to the best of my knowledge it must be
> > set for the first time in this function for valid connections of this event,
> > therefore it should be fine.
> >
> > net/bluetooth/hci_event.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > index 681c623aa380..71ccb12c928d 100644
> > --- a/net/bluetooth/hci_event.c
> > +++ b/net/bluetooth/hci_event.c
> > @@ -3106,6 +3106,17 @@ static void hci_conn_complete_evt(struct hci_dev *hdev, void *data,
> >               }
> >       }
> >
> > +     /* The HCI_Connection_Complete event is only sent once per connection.
> > +      * Processing it more than once per connection can corrupt kernel memory.
> > +      *
> > +      * As the connection handle is set here for the first time, it indicates
> > +      * whether the connection is already set up.
> > +      */
> > +     if (conn->handle) {
> > +             bt_dev_err(hdev, "Ignoring HCI_Connection_Complete for existing connection");
> > +             goto unlock;
> > +     }
> > +
> >       if (!ev->status) {
> >               conn->handle = __le16_to_cpu(ev->handle);
> >



-- 
Luiz Augusto von Dentz