Re: [Patch net v2 1/3] bluetooth: validate HCI_EVENT_PKT packet carefully

[Cong Wang <xiyou.wangcong@gmail.com>]

On Tue, Apr 23, 2019 at 12:42 PM Marcel Holtmann <marcel@holtmann.org> wrote:
>
> Hi Cong,
>
> > hci_event_packet() blindly assumes all packets are sane, at least
> > for packets allocated via vhci_get_user() path this is not true.
> > We have to check if we access skb data out-of-bound with
> > pskb_may_pull() before each skb->data dereference on RX path.
> >
> > Reported-and-tested-by: syzbot+cec7a50c412a2c03f8f5@syzkaller.appspotmail.com
> > Reported-and-tested-by: syzbot+660883c56e2fa65d4497@syzkaller.appspotmail.com
> > Cc: Marcel Holtmann <marcel@holtmann.org>
> > Cc: Johan Hedberg <johan.hedberg@gmail.com>
> > Cc: Dan Carpenter <dan.carpenter@oracle.com>
> > Reviewed-by: Tomas Bortoli <tomasbortoli@gmail.com>
> > Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> > ---
> > net/bluetooth/hci_event.c | 262 +++++++++++++++++++++++++++++++-------
> > 1 file changed, 218 insertions(+), 44 deletions(-)
> >
> > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > index 609fd6871c5a..2fef70c0bffe 100644
> > --- a/net/bluetooth/hci_event.c
> > +++ b/net/bluetooth/hci_event.c
> > @@ -2331,10 +2331,13 @@ static void hci_cs_switch_role(struct hci_dev *hdev, u8 status)
> >
> > static void hci_inquiry_complete_evt(struct hci_dev *hdev, struct sk_buff *skb)
> > {
> > -     __u8 status = *((__u8 *) skb->data);
> >       struct discovery_state *discov = &hdev->discovery;
> >       struct inquiry_entry *e;
> > +     __u8 status;
> >
> > +     if (unlikely(!pskb_may_pull(skb, 1)))
> > +             return;
> > +     status = *((__u8 *)skb->data);
> >       BT_DBG("%s status 0x%2.2x", hdev->name, status);
> >
> >       hci_conn_check_pending(hdev);
> > @@ -2391,14 +2394,21 @@ static void hci_inquiry_complete_evt(struct hci_dev *hdev, struct sk_buff *skb)
> > static void hci_inquiry_result_evt(struct hci_dev *hdev, struct sk_buff *skb)
> > {
> >       struct inquiry_data data;
> > -     struct inquiry_info *info = (void *) (skb->data + 1);
> > -     int num_rsp = *((__u8 *) skb->data);
> > +     struct inquiry_info *info;
> > +     int num_rsp;
> >
> >       BT_DBG("%s num_rsp %d", hdev->name, num_rsp);
> >
> > +     if (unlikely(!pskb_may_pull(skb, 1)))
> > +             return;
> > +     num_rsp = *((__u8 *)skb->data);
> >       if (!num_rsp)
> >               return;
> >
> > +     if (unlikely(!pskb_may_pull(skb, 1 + num_rsp * sizeof(*info))))
> > +             return;
> > +     info = (void *)(skb->data + 1);
> > +
> >       if (hci_dev_test_flag(hdev, HCI_PERIODIC_INQ))
> >               return;
>
> this really looks like we better create a macro for this. It is repetitive code that can be turned into just a macro usage.

Hmm, I have no idea on how to make a macro for this, any hints?

By the way, we use the similar pattern in networking code, I am not
aware of any macro there.

Thanks.