linux-kernel - Re: [PATCH v6 2/2] usb: gadget: udc: core: Prevent soft_connect

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Date:   Thu, 8 Jun 2023 13:47:54 -0700
From:   Badhri Jagan Sridharan <badhri@...gle.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     gregkh@...uxfoundation.org, colin.i.king@...il.com,
        xuetao09@...wei.com, quic_eserrao@...cinc.com,
        water.zhangjiantao@...wei.com, francesco@...cini.it,
        alistair@...stair23.me, stephan@...hold.net, bagasdotme@...il.com,
        luca@...tu.xyz, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v6 2/2] usb: gadget: udc: core: Prevent
 soft_connect_store() race

Thanks Alan ! Just sent out the v7 of the series after fixing all
other comments.

Regards,
Badhri

On Thu, Jun 8, 2023 at 8:27 AM Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Wed, Jun 07, 2023 at 10:17:04PM -0700, Badhri Jagan Sridharan wrote:
> > On Wed, Jun 7, 2023 at 11:26 AM Alan Stern <stern@...land.harvard.edu>
> > wrote:
> > > > @@ -756,10 +772,12 @@ int usb_gadget_disconnect(struct usb_gadget
> > > *gadget)
> > > >       if (!gadget->connected)
> > > >               goto out;
> > > >
> > > > -     if (gadget->deactivated) {
> > > > +     if (gadget->deactivated || !gadget->udc->started) {
> > >
> > > Do you really need to add this extra test?  After all, if the gadget
> > > isn't started then how could the previous test of gadget->connected
> > > possibly succeed?
> > >
> > > In fact, I suspect this entire section of code was always useless, since
> > > the gadget couldn't be connected now if it was already deactivated.
> > >
> >
> > Thanks Alan ! Will fix all other comments in v7 but not sure about this one.
> > Although the ->pullup() function will not be called,
> > -> connected flag could actually be set when the gadget is not started.
> >
> > - if (gadget->deactivated || !gadget->udc->allow_connect) {
> > + if (gadget->deactivated || !gadget->udc->allow_connect ||
> > !gadget->udc->started) {
> >   /*
> >   * If gadget is deactivated we only save new state.
> >   * Gadget will be connected automatically after activation.
> > + *
> > + * udc first needs to be started before gadget can be pulled up.
> >   */
> >   gadget->connected = true;
> >
> > This could happen, for instance, when  usb_udc_vbus_handler()  is invoked
> > after soft_connect_store() disconnects the gadget.
> > Same applies to when usb_gadget_connect() is called after the gadget has
> > been deactivated through usb_gadget_deactivate().
> >
> > This implies that the checks should be there, right ?
>
> Yes, you're right; the checks do need to be there.  I had forgotten
> about these possible cases.  Ignore that comment.
>
> Alan Stern