[PATCH 5.11 311/329] drm/i915/gt: Fix a double free in gen8_preallocate_top_level_pdp

From: Greg Kroah-Hartman
Date: Mon May 17 2021 - 11:59:39 EST

From: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxx>
Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20210426124340.4238-1-lyl2019@xxxxxxxxxxxxxxxx
(cherry picked from commit ac69496fe65cca0611d5917b7d232730ff605bc7)
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
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;