Re: [PATCH] net: usb: fix possible use-after-free in smsc75xx_bind

[Dongliang Mu]

On Tue, Jun 15, 2021 at 3:38 PM Greg KH <greg@xxxxxxxxx> wrote:
>
> On Mon, Jun 14, 2021 at 11:37:12PM +0800, Dongliang Mu wrote:
> > The commit 46a8b29c6306 ("net: usb: fix memory leak in smsc75xx_bind")
> > fails to clean up the work scheduled in smsc75xx_reset->
> > smsc75xx_set_multicast, which leads to use-after-free if the work is
> > scheduled to start after the deallocation. In addition, this patch also
> > removes one dangling pointer - dev->data[0].
> >
> > This patch calls cancel_work_sync to cancel the schedule work and set
> > the dangling pointer to NULL.
> >
> > Fixes: 46a8b29c6306 ("net: usb: fix memory leak in smsc75xx_bind")
> > Signed-off-by: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
> > ---
> >  drivers/net/usb/smsc75xx.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/net/usb/smsc75xx.c b/drivers/net/usb/smsc75xx.c
> > index b286993da67c..f81740fcc8d5 100644
> > --- a/drivers/net/usb/smsc75xx.c
> > +++ b/drivers/net/usb/smsc75xx.c
> > @@ -1504,7 +1504,10 @@ static int smsc75xx_bind(struct usbnet *dev, struct usb_interface *intf)
> >       return 0;
> >
> >  err:
> > +     cancel_work_sync(&pdata->set_multicast);
> >       kfree(pdata);
> > +     pdata = NULL;
>
> Why do you have to set pdata to NULL afterward?
>

It does not have to. pdata will be useless when the function exits. I
just referred to the implementation of smsc75xx_unbind.

> thanks,
>
> greg k-h