linux-kernel - Re: [PATCH v2 3/3] mwifiex: fix division by zero in fw download path

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Message-ID: <YXpPUdj0wJG2L5ra@hovoldconsulting.com>
Date:   Thu, 28 Oct 2021 09:20:49 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Kalle Valo <kvalo@...eaurora.org>,
        Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi017@...il.com>,
        Sharvari Harisangam <sharvari.harisangam@....com>,
        Xinming Hu <huxinming820@...il.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Amitkumar Karwar <akarwar@...vell.com>
Subject: Re: [PATCH v2 3/3] mwifiex: fix division by zero in fw download path

On Wed, Oct 27, 2021 at 11:22:39AM -0700, Brian Norris wrote:
> On Wed, Oct 27, 2021 at 1:12 AM Johan Hovold <johan@...nel.org> wrote:
> > --- a/drivers/net/wireless/marvell/mwifiex/usb.c
> > +++ b/drivers/net/wireless/marvell/mwifiex/usb.c
> > @@ -505,6 +505,22 @@ static int mwifiex_usb_probe(struct usb_interface *intf,
> >                 }
> >         }
> >
> > +       switch (card->usb_boot_state) {
> > +       case USB8XXX_FW_DNLD:
> > +               /* Reject broken descriptors. */
> > +               if (!card->rx_cmd_ep || !card->tx_cmd_ep)
> > +                       return -ENODEV;
> 
> ^^ These two conditions are applicable to USB8XXX_FW_READY too, right?

Right, but I didn't want to add an incomplete set of constraints.

I couldn't find any documentation (e.g. lsusb -v) for what the
descriptors are supposed to look like, but judging from the code,
something like

	if (!card->rx_cmd_ep || !card->tx_cmd_ep)
		return -ENODEV;
	if (!card->rx_data_ep || !card->port[0].tx_data_ep)
		return -ENODEV;

should do. But I'm not sure about the second tx endpoint,
card->port[1].tx_data_ep, for which support was added later and which
the driver appears to be able to manage without.

Either way it has nothing to do with the division-by-zero and should be
added separately.

> > +               if (card->bulk_out_maxpktsize == 0)
> > +                       return -ENODEV;
> > +               break;
> > +       case USB8XXX_FW_READY:
> > +               /* Assume the driver can handle missing endpoints for now. */
> > +               break;
> > +       default:
> > +               WARN_ON(1);
> > +               return -ENODEV;
> > +       }

Johan