Re: [PATCH] nfc: virtual_ncidev: Add variable to check if ndev is running

[Nguyen Dinh Phi]

On 20/11/23 5:06 pm, Krzysztof Kozlowski wrote:
> On 20/11/2023 05:47, Bongsu Jeon wrote:
> > On 20/11/2023 01:47, Nguyen Dinh Phi wrote:
> >
> > > syzbot reported an memory leak that happens when an skb is add to
> > > send_buff after virtual nci closed.
> > > This patch adds a variable to track if the ndev is running before
> > > handling new skb in send function.
> > >
> > > Reported-by: syzbot+6eb09d75211863f15e3e@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > Closes: https://lore.kernel.org/lkml/00000000000075472b06007df4fb@xxxxxxxxxx
> > > Signed-off-by: Nguyen Dinh Phi <phind.uet@xxxxxxxxx>
> > > ---
> > >   drivers/nfc/virtual_ncidev.c | 9 +++++++--
> > >   1 file changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/nfc/virtual_ncidev.c b/drivers/nfc/virtual_ncidev.c
> > > index b027be0b0b6f..ac8226db54e2 100644
> > > --- a/drivers/nfc/virtual_ncidev.c
> > > +++ b/drivers/nfc/virtual_ncidev.c
> > > @@ -20,26 +20,31 @@
> > >                                    NFC_PROTO_ISO14443_MASK | \
> > >                                    NFC_PROTO_ISO14443_B_MASK | \
> > >                                    NFC_PROTO_ISO15693_MASK)
> > > +#define NCIDEV_RUNNING 0
> > This define isn't used.
> >
> > >   
> > >   struct virtual_nci_dev {
> > >           struct nci_dev *ndev;
> > >           struct mutex mtx;
> > >           struct sk_buff *send_buff;
> > >           struct wait_queue_head wq;
> > > +        bool running;
> > >   };
> > >   
> > >   static int virtual_nci_open(struct nci_dev *ndev)
> > >   {
> > > +        struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
> > > +
> > > +        vdev->running = true;
> > >           return 0;
> > >   }
> > >   
> > >   static int virtual_nci_close(struct nci_dev *ndev)
> > >   {
> > >           struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
> > > -
> > >           mutex_lock(&vdev->mtx);
> > >           kfree_skb(vdev->send_buff);
> > >           vdev->send_buff = NULL;
> > > +        vdev->running = false;
> > >           mutex_unlock(&vdev->mtx);
> > >   
> > >           return 0;
> > > @@ -50,7 +55,7 @@ static int virtual_nci_send(struct nci_dev *ndev, struct sk_buff *skb)
> > >           struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
> > >   
> > >           mutex_lock(&vdev->mtx);
> > > -        if (vdev->send_buff) {
> > > +        if (vdev->send_buff || !vdev->running) {
> >
> > Dear Krzysztof,
> >
> > I agree this defensive code.
> > But i think NFC submodule has to avoid this situation.(calling send function of closed nci_dev)
> > Could you check this?
>
> This code looks not effective. At this point vdev->send_buff is always
> false, so the additional check would not bring any value.
>
> I don't see this fixing anything. Syzbot also does not seem to agree.
>
> Nguyen, please test your patches against syzbot *before* sending them.
> If you claim this fixes the report, please provide me the link to syzbot
> test results confirming it is fixed.
>
> I looked at syzbot dashboard and do not see this issue fixed with this
> patch.
>
> Best regards,
> Krzysztof

Hi Krzysztof,

I've submitted it to syzbot, it is the test request that created at 
[2023/11/20 09:39] in dashboard link 
https://syzkaller.appspot.com/bug?extid=6eb09d75211863f15e3e

Best regards,
Phi