Re: [PATCH] ath9k: fix stack-out-of-bounds Write in ath9k_hif_usb_rx_cb

[Qiujun Huang]

On Tue, Mar 31, 2020 at 7:03 PM Kalle Valo <kvalo@xxxxxxxxxxxxxx> wrote:
>
> Qiujun Huang <hqjagain@xxxxxxxxx> writes:
>
> > Add barrier to accessing the stack array skb_pool.
> >
> > Reported-by: syzbot+d403396d4df67ad0bd5f@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Qiujun Huang <hqjagain@xxxxxxxxx>
> > ---
> >  drivers/net/wireless/ath/ath9k/hif_usb.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/net/wireless/ath/ath9k/hif_usb.c b/drivers/net/wireless/ath/ath9k/hif_usb.c
> > index dd0c323..c4a2b72 100644
> > --- a/drivers/net/wireless/ath/ath9k/hif_usb.c
> > +++ b/drivers/net/wireless/ath/ath9k/hif_usb.c
> > @@ -612,6 +612,11 @@ static void ath9k_hif_usb_rx_stream(struct hif_device_usb *hif_dev,
> >                       hif_dev->remain_skb = nskb;
> >                       spin_unlock(&hif_dev->rx_lock);
> >               } else {
> > +                     if (pool_index == MAX_PKT_NUM_IN_TRANSFER) {
> > +                             dev_err(&hif_dev->udev->dev,
> > +                                     "ath9k_htc: over RX MAX_PKT_NUM\n");
> > +                             goto err;
the  barrier ensure pool_index <= MAX_PKT_NUM_IN_TRANSFER
> > +                     }
>
> What about 'pool_index >= MAX_PKT_NUM_IN_TRANSFER' just to be on the
> safe side? Ah, but then error handling won't work:
It looks ok?
it can handle the case: pool_index == MAX_PKT_NUM_IN_TRANSFER
>
> err:
>         for (i = 0; i < pool_index; i++) {
>                 RX_STAT_ADD(skb_completed_bytes, skb_pool[i]->len);
>                 ath9k_htc_rx_msg(hif_dev->htc_handle, skb_pool[i],
>                                  skb_pool[i]->len, USB_WLAN_RX_PIPE);
>                 RX_STAT_INC(skb_completed);
>         }
>
> Maybe that should use 'min(pool_index, MAX_PKT_NUM_IN_TRANSFER - 1)' or
> something? Or maybe it's just overengineerin, dunno.
>
> --
> https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches