linux-kernel - Re: [PATCH] usb: gadget: rndis: Avoid dereference before NULL check

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Message-ID: <YxuA7yTtUmYdDD9A@kroah.com>
Date:   Fri, 9 Sep 2022 20:07:43 +0200
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Jim Lin <jilin@...dia.com>
Cc:     "s.shtylyov@....ru" <s.shtylyov@....ru>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Aniruddha Tvs Rao <anrao@...dia.com>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] usb: gadget: rndis: Avoid dereference before NULL check

On Fri, Sep 09, 2022 at 02:43:14PM +0000, Jim Lin wrote:
> On Fri, 2022-09-09 at 07:38 +0200, Greg KH wrote:
> > External email: Use caution opening links or attachments
> > 
> > 
> > On Fri, Sep 09, 2022 at 01:56:15AM +0800, Jim Lin wrote:
> > > NULL check is performed after params->dev is dereferenced in
> > > dev_get_stats.
> > 
> > I do not understand this statement.
> > 
> > > Fixed by adding a NULL check before dereferencing params->dev and
> > > removing subsequent NULL checks for it.
> > > 
> > > Signed-off-by: Aniruddha TVS Rao <anrao@...dia.com>
> > > Signed-off-by: Jim Lin <jilin@...dia.com>
> > > ---
> > >  drivers/usb/gadget/function/rndis.c | 37 ++++++++++++-------------
> > > ----
> > >  1 file changed, 15 insertions(+), 22 deletions(-)
> > > 
> > > diff --git a/drivers/usb/gadget/function/rndis.c
> > > b/drivers/usb/gadget/function/rndis.c
> > > index 64de9f1b874c..d2f18f34c8e5 100644
> > > --- a/drivers/usb/gadget/function/rndis.c
> > > +++ b/drivers/usb/gadget/function/rndis.c
> > > @@ -198,6 +198,9 @@ static int gen_ndis_query_resp(struct
> > > rndis_params *params, u32 OID, u8 *buf,
> > >       outbuf = (__le32 *)&resp[1];
> > >       resp->InformationBufferOffset = cpu_to_le32(16);
> > > 
> > > +     if (!params->dev)
> > > +             return -ENODEV;
> > > +
> > 
> > As Sergey points out, this check is useless and the ones below should
> > also be removed.
> > 
> > But, why make this check at all, how did you trigger a problem with
> > the
> > current code?
> > 
> > Are you using this driver?  If so, why?  It is totally broken (as per
> > the specification) and we really really need to just delete it from
> > the
> > tree to prevent anyone else from ever using it.
> > 
> > thanks,
> > 
> > greg k-h
> Thanks for review, please ignore this patch.
> Issue was triggered by our internal tool (probably not smart enough,
> and cause false alarm).

Ah, so that means I HAVE to reject it as you did not properly follow the
requirements when you use tools like this.  Please read
Documentation/process/researcher-guidelines.rst for how to do this
properly.

That is now a requirement to make it so that we are not the ones doing
the debugging of random tools like we just had to do here...

You owe me 3 patch reviews now :)

thanks,

greg k-h