[Intel-gfx] [PATCH] drm/i915: Fix use after free in lpe_audio_platdev_destroy()
Takashi Iwai
tiwai at suse.de
Wed Apr 12 04:59:55 UTC 2017
On Tue, 11 Apr 2017 23:27:07 +0200,
Chris Wilson wrote:
>
> On Tue, Apr 11, 2017 at 10:20:56PM +0100, Chris Wilson wrote:
> > On Tue, Apr 11, 2017 at 11:01:57PM +0200, Takashi Iwai wrote:
> > > On Tue, 11 Apr 2017 22:41:12 +0200,
> > > Chris Wilson wrote:
> > > Oh, this fell into a crack as it was sent just before my vacation.
> > >
> > > About the change:
> > >
> > > > > ---
> > > > > drivers/gpu/drm/i915/intel_lpe_audio.c | 8 ++++++--
> > > > > 1 file changed, 6 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/i915/intel_lpe_audio.c b/drivers/gpu/drm/i915/intel_lpe_audio.c
> > > > > index 7a5b41b1c024..32000902a204 100644
> > > > > --- a/drivers/gpu/drm/i915/intel_lpe_audio.c
> > > > > +++ b/drivers/gpu/drm/i915/intel_lpe_audio.c
> > > > > @@ -131,8 +131,12 @@ lpe_audio_platdev_create(struct drm_i915_private *dev_priv)
> > > > >
> > > > > static void lpe_audio_platdev_destroy(struct drm_i915_private *dev_priv)
> > > > > {
> > > > > - platform_device_unregister(dev_priv->lpe_audio.platdev);
> > > > > - kfree(dev_priv->lpe_audio.platdev->dev.dma_mask);
> > > > > + struct platform_device *platdev = dev_priv->lpe_audio.platdev;
> > > > > +
> > > > > + kfree(platdev->dev.dma_mask);
> > > > > + platdev->dev.dma_mask = NULL;
> > > > > +
> > > > > + platform_device_unregister(platdev);
> > >
> > > I'm not sure whether it's good idea to fiddle dma_mask bits before the
> > > unregister call. Interestingly, this is the only driver that calls
> > > kfree() for pdev's dma_mask. Either we do something wrong, or
> > > everyone forgot this?
> >
> > Afaict, everyone else chose the blissful ignorance strategy and we are
> > the only fools to try and free the dma_mask.
> >
> > Would you feel more comfortable with:
> >
> > void *mask = platdev->dev.dma_mask;
> >
> > platform_device_unregister(platdev);
> >
> > /* XXX see platform_device_register_full():
> > * "This memory isn't freed when the device is put."
> > * It's not clear why it hasn't been fixed in a decade...
> > */
> > kfree(mask);
>
> Still has the issue that unregister may not the final put, it should but
> still...
>
> I think we just leak the memory. We are not the owner and so shouldn't
> be fiddling around trying to free it.
Agreed, IMO, we should handle better in the platform device side.
thanks,
Takashi
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