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

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Date:   Mon, 5 Sep 2022 15:46:09 +0800
From:   Zheng Hacker <hackerzheng666@...il.com>
To:     xmzyshypnc <1002992920@...com>
Cc:     airlied@...ux.ie, daniel@...ll.ch, zhenyuw@...ux.intel.com,
        zhi.a.wang@...el.com, alex000young@...il.com,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, tvrtko.ursulin@...ux.intel.com,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, security@...nel.org,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry.

I rewrote the letter. Hope it works.

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 returning the result of ppgtt_invalidate_spt to split_2MB_gtt_entry.

Signed-off-by: Zheng Wang

---
 drivers/gpu/drm/i915/gvt/gtt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index ce0eb03709c3..9f14fded8c0c 100644
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -1215,7 +1215,7 @@ static int split_2MB_gtt_entry(struct intel_vgpu *vgpu,
                ret = intel_gvt_dma_map_guest_page(vgpu, start_gfn + sub_index,
                                                   PAGE_SIZE, &dma_addr);
                if (ret) {
-                       ppgtt_invalidate_spt(spt);
+                       ret = ppgtt_invalidate_spt(spt);
                        return ret;
                }
                sub_se.val64 = se->val64;
--
2.25.1