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

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Date:   Fri, 16 Sep 2022 10:25:50 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zheng Hacker <hackerzheng666@...il.com>
Cc:     Zhenyu Wang <zhenyuw@...ux.intel.com>,
        "alex000young@...il.com" <alex000young@...il.com>,
        "security@...nel.org" <security@...nel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "tvrtko.ursulin@...ux.intel.com" <tvrtko.ursulin@...ux.intel.com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        xmzyshypnc <1002992920@...com>,
        "jani.nikula@...ux.intel.com" <jani.nikula@...ux.intel.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "rodrigo.vivi@...el.com" <rodrigo.vivi@...el.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "zhi.a.wang@...el.com" <zhi.a.wang@...el.com>
Subject: Re: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry.

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@...com>
> 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@...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 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