linux-kernel - Re: [PATCH] media: flexcop-usb: fix sanity check of bNumEndpoints

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Message-ID: <CAD-N9QVQpm87wpCnLj08db3kAr=b191op3=ESOMm1yh7UWu4jw@mail.gmail.com>
Date:   Fri, 10 Jun 2022 09:27:27 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Johan Hovold <johan@...nel.org>
Cc:     Dongliang Mu <dzm91@...t.edu.cn>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        gushengxian <gushengxian@...ong.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Oliver Neukum <oneukum@...e.com>, Sean Young <sean@...s.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        linux-media@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: flexcop-usb: fix sanity check of bNumEndpoints

On Thu, Jun 9, 2022 at 10:00 PM Johan Hovold <johan@...nel.org> wrote:
>
> On Thu, Jun 09, 2022 at 09:42:15AM +0800, Dongliang Mu wrote:
> > On Thu, Jun 2, 2022 at 2:45 PM Johan Hovold <johan@...nel.org> wrote:
> > >
> > > On Thu, Jun 02, 2022 at 01:50:24PM +0800, Dongliang Mu wrote:
> > > > From: Dongliang Mu <mudongliangabcd@...il.com>
> > > >
> > > > Commit d725d20e81c2 ("media: flexcop-usb: sanity checking of endpoint type
> > > > ") adds a sanity check for endpoint[1], but fails to modify the sanity
> > > > check of bNumEndpoints.
> > > >
> > > > Fix this by modifying the sanity check of bNumEndpoints to 2.
> > >
> > > Are you sure that d725d20e81c2 ("media: flexcop-usb: sanity checking of
> > > endpoint type) was correct?
> >
> > I am not sure if fc_usb->uintf->cur_altsetting->endpoint[1] is right or not.
> >
> > But the sanity check of bNumEndpoints does not match the following dereference.
>
> I should know better than try to be subtle on the internet: Your fix is
> wrong.
>
> You need to try to understand the code you're changing. Not just do
> pattern matching.

I see. Yeah, I have such an incorrect assumption - previous commits
should be somehow correct since maintainers already review them.

Next time, I will dig more about the code logic and try to post a more
comprehensive patch.

>
> > > > Fixes: d725d20e81c2 ("media: flexcop-usb: sanity checking of endpoint type")
> > > > Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
> > > > ---
> > > >  drivers/media/usb/b2c2/flexcop-usb.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/media/usb/b2c2/flexcop-usb.c b/drivers/media/usb/b2c2/flexcop-usb.c
> > > > index 7835bb0f32fc..eb54bfdda01f 100644
> > > > --- a/drivers/media/usb/b2c2/flexcop-usb.c
> > > > +++ b/drivers/media/usb/b2c2/flexcop-usb.c
> > > > @@ -509,7 +509,7 @@ static int flexcop_usb_init(struct flexcop_usb *fc_usb)
> > > >               return ret;
> > > >       }
> > > >
> > > > -     if (fc_usb->uintf->cur_altsetting->desc.bNumEndpoints < 1)
> > > > +     if (fc_usb->uintf->cur_altsetting->desc.bNumEndpoints < 2)
> > > >               return -ENODEV;
> > > >       if (!usb_endpoint_is_isoc_in(&fc_usb->uintf->cur_altsetting->endpoint[1].desc))
> > > >               return -ENODEV;
> > >
> > > It looks like it should have verified the type of endpoint[0] here
> > > instead.
> >
> > This sanity check originally makes sure the
> > fc_usb->uintf->cur_altsetting->endpoint[0] in
> > flexcop_usb_transfer_init.
>
> Yes, and that is the only endpoint that this driver uses.

This needs an understanding of the working mechanism of this hardware.

>
> I've posted a fix here:
>
>         https://lore.kernel.org/r/20220609135341.19941-1-johan@kernel.org
>
> Johan