linux-kernel - [PATCH 5.11 311/329] drm/i915/gt: Fix a double free in gen8_preallocate_top_level

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Date:   Mon, 17 May 2021 16:03:42 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lv Yunlong <lyl2019@...l.ustc.edu.cn>,
        Matthew Auld <matthew.auld@...el.com>,
        Jani Nikula <jani.nikula@...el.com>
Subject: [PATCH 5.11 311/329] drm/i915/gt: Fix a double free in gen8_preallocate_top_level_pdp

From: Lv Yunlong <lyl2019@...l.ustc.edu.cn>

commit ea995218dddba171fecd05496c69617c5ef3c5b8 upstream.

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>
Reviewed-by: Matthew Auld <matthew.auld@...el.com>
Signed-off-by: Matthew Auld <matthew.auld@...el.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210426124340.4238-1-lyl2019@mail.ustc.edu.cn
(cherry picked from commit ac69496fe65cca0611d5917b7d232730ff605bc7)
Signed-off-by: Jani Nikula <jani.nikula@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/i915/gt/gen8_ppgtt.c |    1 -
 1 file changed, 1 deletion(-)

--- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
+++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
@@ -631,7 +631,6 @@ static int gen8_preallocate_top_level_pd
 
 		err = pin_pt_dma(vm, pde->pt.base);
 		if (err) {
-			i915_gem_object_put(pde->pt.base);
 			free_pd(vm, pde);
 			return err;
 		}