netdev - Re: [PATCH] nfc: Allow to create multiple virtual nci devices

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Date:   Thu, 3 Nov 2022 11:18:58 -0700
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     bongsu.jeon@...sung.com, krzysztof.kozlowski@...aro.org,
        netdev@...r.kernel.org, syzkaller@...glegroups.com
Subject: Re: [PATCH] nfc: Allow to create multiple virtual nci devices

On Mon, 31 Oct 2022 at 23:06, Leon Romanovsky <leon@...nel.org> wrote:
>
> On Mon, Oct 31, 2022 at 08:36:57AM -0700, Dmitry Vyukov wrote:
> > On Mon, 31 Oct 2022 at 02:23, Leon Romanovsky <leon@...nel.org> wrote:
> > >
> > > On Sun, Oct 30, 2022 at 03:29:19PM +0100, Dmitry Vyukov wrote:
> > > > The current virtual nci driver is great for testing and fuzzing.
> > > > But it allows to create at most one "global" device which does not allow
> > > > to run parallel tests and harms fuzzing isolation and reproducibility.
> > > > Restructure the driver to allow creation of multiple independent devices.
> > > > This should be backwards compatible for existing tests.
> > > >
> > > > Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
> > > > Cc: Bongsu Jeon <bongsu.jeon@...sung.com>
> > > > Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> > > > Cc: netdev@...r.kernel.org
> > > > ---
> > > >  drivers/nfc/virtual_ncidev.c | 143 ++++++++++++++++-------------------
> > > >  1 file changed, 66 insertions(+), 77 deletions(-)
> > >
> > > <...>
> > >
> > > >  static int virtual_nci_send(struct nci_dev *ndev, struct sk_buff *skb)
> > > >  {
> > > > -     mutex_lock(&nci_mutex);
> > > > -     if (state != virtual_ncidev_enabled) {
> > > > -             mutex_unlock(&nci_mutex);
> > > > -             kfree_skb(skb);
> > > > -             return 0;
> > > > -     }
> > > > +     struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
> > > >
> > > > -     if (send_buff) {
> > > > -             mutex_unlock(&nci_mutex);
> > > > +     mutex_lock(&vdev->mtx);
> > > > +     if (vdev->send_buff) {
> > > > +             mutex_unlock(&vdev->mtx);
> > > >               kfree_skb(skb);
> > >
> > > You probably need to set vdev->send_buff to NULL here.
> >
> > Hi Leon,
> >
> > Thanks for looking at this.
> >
> > Are you sure about setting vdev->send_buff to NULL?
> > We already have a "cached" skb in vdev->send_buff, we received a new
> > one in 'skb' and freed it.
> > I assumed the intention is to keep vdev->send_buff intact.
>
> You are right.
>
> >
> > > >               return -1;
> > > >       }
> > > > -     send_buff = skb_copy(skb, GFP_KERNEL);
> > > > -     mutex_unlock(&nci_mutex);
> > > > -     wake_up_interruptible(&wq);
> > > > +     vdev->send_buff = skb_copy(skb, GFP_KERNEL);
> > >
> > > You don't check return value of skb_copy(), it can fail, but
> > > this function will return 0 (success). Do you do it deliberately?
> > >
> > > If yes, please add a comment to the code, as it is not clear.
> >
> > Good question. I just kept all of this logic as it is now and only
> > removed the global vars.
>
> I know :)
>
> >
> > I guess we need something like this, right?
> >
> > vdev->send_buff = skb_copy(skb, GFP_KERNEL);
> > if (!vdev->send_buff) {
> >     mutex_unlock(&vdev->mtx);
> >     return -1;
> > }
> >
> > Though, it's called only from nci_send_frame() and its return value is
> > never checked :)
>
> I would say that the most important part is do not continue after
> skb_copy() failure.

Mailed v2 with this fix.

> Thanks
>
> >
> > $ git grep nci_send_frame
> > include/net/nfc/nci_core.h:int nci_send_frame(struct nci_dev *ndev,
> > struct sk_buff *skb);
> > net/nfc/nci/core.c:int nci_send_frame(struct nci_dev *ndev, struct sk_buff *skb)
> > net/nfc/nci/core.c:EXPORT_SYMBOL(nci_send_frame);
> > drivers/nfc/nfcmrvl/fw_dnld.c:
> > nci_send_frame(priv->ndev, out_skb);
> > drivers/nfc/nfcmrvl/fw_dnld.c:          nci_send_frame(priv->ndev, out_skb);
> > drivers/nfc/nfcmrvl/fw_dnld.c:
> > nci_send_frame(priv->ndev, out_skb);
> > net/nfc/nci/core.c:             nci_send_frame(ndev, skb);
> > net/nfc/nci/core.c:             nci_send_frame(ndev, skb);
> >
> >
> > > Thanks
> > >
> > > > +     mutex_unlock(&vdev->mtx);
> > > > +     wake_up_interruptible(&vdev->wq);
> > > >       consume_skb(skb);
> > > >
> > > >       return 0;