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

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Message-ID: <Yzmds3DXu32EeSO5@kroah.com>
Date:   Sun, 2 Oct 2022 16:18:27 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zheng Wang <zyytlz.wz@....com>
Cc:     hackerzheng666@...il.com, 1002992920@...com, airlied@...ux.ie,
        alex000young@...il.com, dri-devel@...ts.freedesktop.org,
        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] drm/i915/gvt: fix double free bug in split_2MB_gtt_entry

On Wed, Sep 28, 2022 at 11:33:40AM +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 only freeing spt in ppgtt_invalidate_spt in good case.
> 
> Fixes: b901b252b6cf ("drm/i915/gvt: Add 2M huge gtt support")
> Reported-by: Zheng Wang <hackerzheng666@...il.com>
> Signed-off-by: Zheng Wang <zyytlz.wz@....com>
> ---
>  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);

That is a horrible way to make an api (and it should be a bool too.)

Now every time you see this call in the code, you have to go look up
what the last parameter means.  Just make 2 functions, one that does the
"is error" thing, and one that does not, and that will be much easier to
maintain and understand for the next 10+ years.

thanks,

greg k-h