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

[Greg KH]

On Fri, Sep 16, 2022 at 11:54:42PM +0800, Zheng Hacker wrote:
> >From afe79848cb74cc8e45ab426d13fa2394c87e0422 Mon Sep 17 00:00:00 2001
> From: xmzyshypnc <1002992920@xxxxxx>
> Date: Fri, 16 Sep 2022 23:48:23 +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: Zheng Wang <hackerzheng666@xxxxxxxxx>
> ---
>  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 ce0eb03709c3..550519f0acca 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 *spt, int
> is_error);
> 
>  static int ppgtt_invalidate_spt_by_shadow_entry(struct intel_vgpu *vgpu,
>         struct intel_gvt_gtt_entry *e)
> @@ -995,7 +995,7 @@ static int
> ppgtt_invalidate_spt_by_shadow_entry(struct intel_vgpu *vgpu,

Still line-wrapped and whitespace broken :(