linux-kernel - Re: [PATCH v2] sound/hda: Add NULL check to component match callback function

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Date:   Thu, 31 Mar 2022 14:56:41 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Takashi Iwai <tiwai@...e.de>, Won Chung <wonchung@...gle.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Benson Leung <bleung@...omium.org>,
        Prashant Malani <pmalani@...omium.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] sound/hda: Add NULL check to component match callback
 function

On Thu, Mar 31, 2022 at 03:52:14PM +0300, Heikki Krogerus wrote:
> Hi Greg,
> 
> On Thu, Mar 31, 2022 at 01:39:51PM +0200, Greg KH wrote:
> > On Thu, Mar 31, 2022 at 12:25:43PM +0300, Heikki Krogerus wrote:
> > > On Thu, Mar 31, 2022 at 11:12:55AM +0200, Takashi Iwai wrote:
> > > > > > > -     if (!strcmp(dev->driver->name, "i915") &&
> > > > > > > +     if (dev->driver && !strcmp(dev->driver->name, "i915") &&
> > > > > >
> > > > > > Can NULL dev->driver be really seen?  I thought the components are
> > > > > > added by the drivers, hence they ought to have the driver field set.
> > > > > > But there can be corner cases I overlooked.
> > > > > >
> > > > > >
> > > > > > thanks,
> > > > > >
> > > > > > Takashi
> > > > > 
> > > > > Hi Takashi,
> > > > > 
> > > > > When I try using component_add in a different driver (usb4 in my
> > > > > case), I think dev->driver here is NULL because the i915 drivers do
> > > > > not have their component master fully bound when this new component is
> > > > > registered. When I test it, it seems to be causing a crash.
> > > > 
> > > > Hm, from where component_add*() is called?  Basically dev->driver must
> > > > be already set before the corresponding driver gets bound at
> > > > __driver_probe_deviec().  So, if the device is added to component from
> > > > the corresponding driver's probe, dev->driver must be non-NULL.
> > > 
> > > The code that declares a device as component does not have to be the
> > > driver of that device.
> > > 
> > > In our case the components are USB ports, and they are devices that
> > > are actually never bind to any drivers: drivers/usb/core/port.c
> > 
> > Why is a USB device being passed to this code that assumes it is looking
> > for a PCI device with a specific driver name?  As I mentioned on the
> > mei patch, triggering off of a name is really a bad idea, as is assuming
> > the device type without any assurance it is such a device (there's a
> > reason we didn't provide device type identification in the driver core,
> > don't abuse that please...)
> 
> I totally agree. This driver is making a whole bunch of assumptions
> when it should not make any assumptions. And yes, one of those
> assumptions is that the driver of the device has a specific name, and
> that is totally crazy. So why is it making those assumptions? I have
> no idea, but is does, and they are now causing the first problem -
> NULL pointer dereference.
> 
> This patch (and that other) is only proposing a simple way to solve
> that NULL pointer dereference issue by adding some sanity checks. If
> that's no OK, and the whole driver should be refactored instead, then
> that is perfectly OK by me, but that has to be done by somebody who
> understands what exactly is the driver and the device it's controlling
> doing (and for).

This all needs to be refactored to not do this at all.

thanks,

greg k-h