linux-kernel - Re: usb/sound/bcd2000: warning in bcd2000_init

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Message-ID: <20171003174221.GA13006@kroah.com>
Date:   Tue, 3 Oct 2017 19:42:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Takashi Iwai <tiwai@...e.de>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        alsa-devel@...a-project.org,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>, linux-usb@...r.kernel.org
Subject: Re: usb/sound/bcd2000: warning in bcd2000_init_device

On Tue, Oct 03, 2017 at 12:50:08PM -0400, Alan Stern wrote:
> On Tue, 3 Oct 2017, Takashi Iwai wrote:
> 
> > > It's a dev_WARN because it indicates a potentially serious error in the 
> > > driver: The driver has submitted an interrupt URB to a bulk endpoint.  
> > > That may not sound bad, but the same check gets triggered if a driver 
> > > submits a bulk URB to an isochronous endpoint, or any other invalid 
> > > combination.
> > > 
> > > Most likely the explanation here is that the driver doesn't bother to
> > > check the endpoint type because it expects the endpoint will always be
> > > interrupt.  But that is not a safe strategy.  USB devices and their
> > > firmware should not be trusted unnecessarily.
> > > 
> > > The best fix is, like you said, to add a sanity check in the caller.
> > 
> > OK, but then do we have some handy helper for the check?
> > As other bug reports by syzkaller suggest, there are a few other
> > drivers that do the same, submitting a urb with naive assumption of
> > the fixed EP for specific devices.  In the end we'll need to put the
> > very same checks there in multiple places.
> 
> Perhaps we could add a helper routine that would take a list of 
> expected endpoint types and check that the actual endpoints match the 
> types.  But of course, all the drivers you're talking about would have 
> to add a call to this helper routine.

We have almost this type of function, usb_find_common_endpoints(),
what's wrong with using that?  Johan has already swept the tree and
added a lot of these checks, odds are no one looked at the sound/
subdir...

thanks,

greg k-h