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drm/i915: Prevent use-after-free in invalidate_range_start callback

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It's possible for invalidate_range_start mmu notifier callback to race
against userptr object release. If the gem object was released prior to
obtaining the spinlock in invalidate_range_start we're hitting null
pointer dereference.

Testcase: igt/gem_userptr_blits/stress-mm-invalidate-close
Testcase: igt/gem_userptr_blits/stress-mm-invalidate-close-overlap
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
[Jani: added code comment suggested by Chris]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
This commit is contained in:
Michał Winiarski 2015-02-03 15:48:17 +01:00 committed by Jani Nikula
parent 1293eaa3eb
commit 460822b0b1
1 changed files with 18 additions and 2 deletions
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20
drivers/gpu/drm/i915/i915_gem_userptr.c
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@ -113,7 +113,10 @@ restart:
continue;
obj = mo->obj;
drm_gem_object_reference(&obj->base);
if (!kref_get_unless_zero(&obj->base.refcount))
continue;
spin_unlock(&mn->lock);
cancel_userptr(obj);
@ -149,7 +152,20 @@ static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
it = interval_tree_iter_first(&mn->objects, start, end);
if (it != NULL) {
obj = container_of(it, struct i915_mmu_object, it)->obj;
drm_gem_object_reference(&obj->base);
/* The mmu_object is released late when destroying the
* GEM object so it is entirely possible to gain a
* reference on an object in the process of being freed
* since our serialisation is via the spinlock and not
* the struct_mutex - and consequently use it after it
* is freed and then double free it.
*/
if (!kref_get_unless_zero(&obj->base.refcount)) {
spin_unlock(&mn->lock);
serial = 0;
continue;
}
serial = mn->serial;
}
spin_unlock(&mn->lock);