From 460822b0b1a77db859b0320469799fa4dbe4d367 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Micha=C5=82=20Winiarski?= Date: Tue, 3 Feb 2015 15:48:17 +0100 Subject: [PATCH] drm/i915: Prevent use-after-free in invalidate_range_start callback MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Michał Winiarski Reviewed-by: Chris Wilson Cc: stable@vger.kernel.org [Jani: added code comment suggested by Chris] Signed-off-by: Jani Nikula --- drivers/gpu/drm/i915/i915_gem_userptr.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c index d182058383a9..1719078c763a 100644 --- a/drivers/gpu/drm/i915/i915_gem_userptr.c +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c @@ -113,7 +113,10 @@ static void *invalidate_range__linear(struct i915_mmu_notifier *mn, 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); -- GitLab