linux-kernel - Re: [PATCH v2] drm/i915/gvt: fix double free bug in split_2MB_gtt

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Date:   Thu, 6 Oct 2022 21:23:15 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zheng Wang <zyytlz.wz@....com>
Cc:     1002992920@...com, airlied@...ux.ie, alex000young@...il.com,
        dri-devel@...ts.freedesktop.org, hackerzheng666@...il.com,
        intel-gfx@...ts.freedesktop.org, jani.nikula@...ux.intel.com,
        linux-kernel@...r.kernel.org, security@...nel.org,
        tvrtko.ursulin@...ux.intel.com
Subject: Re: [PATCH v2] drm/i915/gvt: fix double free bug in
 split_2MB_gtt_entry

On Fri, Oct 07, 2022 at 12:58:45AM +0800, Zheng Wang wrote:
> If intel_gvt_dma_map_guest_page failed, it will call
> ppgtt_invalidate_spt, which will finally free the spt.
> But the caller does not notice that, it will free spt again in error path.
> 
> Fix this by spliting invalidate and free in ppgtt_invalidate_spt.
> Only free spt when in good case.
> 
> Reported-by: Zheng Wang <hackerzheng666@...il.com>
> Signed-off-by: Zheng Wang <zyytlz.wz@....com>
> ---
> v2:
> - split initial function into two api function suggested by Greg
> 
> v1: https://lore.kernel.org/all/20220928033340.1063949-1-zyytlz.wz@163.com/
> ---
>  drivers/gpu/drm/i915/gvt/gtt.c | 31 +++++++++++++++++++++----------
>  1 file changed, 21 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index ce0eb03709c3..55d8e1419302 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -959,6 +959,7 @@ static inline int ppgtt_put_spt(struct intel_vgpu_ppgtt_spt *spt)
>  	return atomic_dec_return(&spt->refcount);
>  }
>  
> +static int  ppgtt_invalidate_and_free_spt(struct intel_vgpu_ppgtt_spt *spt);

Odd extra space after the 'int', why?