linux-kernel - [PATCH] drm/i9i5/gt: Fix a double free in gen8_preallocate_top_level

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Message-Id: <20210426124340.4238-1-lyl2019@mail.ustc.edu.cn>
Date:   Mon, 26 Apr 2021 05:43:40 -0700
From:   Lv Yunlong <lyl2019@...l.ustc.edu.cn>
To:     jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, airlied@...ux.ie, daniel@...ll.ch,
        chris@...is-wilson.co.uk
Cc:     intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Subject: [PATCH] drm/i9i5/gt: Fix a double free in gen8_preallocate_top_level_pdp

Our code analyzer reported a double free bug.

In gen8_preallocate_top_level_pdp, pde and pde->pt.base are allocated
via alloc_pd(vm) with one reference. If pin_pt_dma() failed, pde->pt.base
is freed by i915_gem_object_put() with a reference dropped. Then free_pd
calls free_px() defined in intel_ppgtt.c, which calls i915_gem_object_put()
to put pde->pt.base again.

As pde->pt.base is protected by refcount, so the second put will not free
pde->pt.base actually. But, maybe it is better to remove the first put?

Fixes: 82adf901138cc ("drm/i915/gt: Shrink i915_page_directory's slab bucket")
Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
---
 drivers/gpu/drm/i915/gt/gen8_ppgtt.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
index 755522ced60d..3ae16945bd43 100644
--- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
+++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
@@ -630,7 +630,6 @@ static int gen8_preallocate_top_level_pdp(struct i915_ppgtt *ppgtt)
 
 		err = pin_pt_dma(vm, pde->pt.base);
 		if (err) {
-			i915_gem_object_put(pde->pt.base);
 			free_pd(vm, pde);
 			return err;
 		}
-- 
2.25.1