Re: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry.

[Zheng Hacker]

Hi greg,

Thanks for pointing that out. Working on it now :)

Best wishes,
Zheng Wang

Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 于2022年9月16日周五 16:25写道：
>
> On Fri, Sep 16, 2022 at 02:39:21PM +0800, Zheng Hacker wrote:
> > >From 8d95c1399e3ff345500a575e21254a73b0c89144 Mon Sep 17 00:00:00 2001
> > From: xmzyshypnc <1002992920@xxxxxx>
> > Date: Fri, 16 Sep 2022 14:37:48 +0800
> > Subject: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry
> >
> > There is a double-free security bug in split_2MB_gtt_entry.
> >
> > Here is a calling chain :
> > ppgtt_populate_spt->ppgtt_populate_shadow_entry->split_2MB_gtt_entry.
> > If intel_gvt_dma_map_guest_page failed, it will call
> > ppgtt_invalidate_spt, which will finally call ppgtt_free_spt and
> > kfree(spt). But the caller does not notice that, and it will call
> > ppgtt_free_spt again in error path.
> >
> > Fix this by only freeing spt in ppgtt_invalidate_spt in good case.
> >
> > Signed-off-by: xmzyshypnc <1002992920@xxxxxx>
> > ---
> >  drivers/gpu/drm/i915/gvt/gtt.c | 16 +++++++++-------
> >  1 file changed, 9 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> > index 9f14fded8c0c..31d2a8d56384 100644
> > --- a/drivers/gpu/drm/i915/gvt/gtt.c
> > +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> > @@ -959,7 +959,7 @@ static inline int ppgtt_put_spt(struct
> > intel_vgpu_ppgtt_spt *spt)
> >   return atomic_dec_return(&spt->refcount);
> >  }
> >
> > -static int ppgtt_invalidate_spt(struct intel_vgpu_ppgtt_spt *spt);
> > +static int ppgtt_invalidate_spt(struct intel_vgpu_ppgtt_spt *sptm,
> > int is_error);
>
> Your patch is whitespace damaged and linewrapped and can not be applied,
> and can only barely read :(
>
> Please fix up your email client to not do this so that the change can be
> properly reviewed and accepted if correct.
>
> thanks,
>
> greg k-h