Add a KUnit test that reproduces the drm_sched_fence timeline-name use-after-free fixed by the previous patch. It submits a job on the mock scheduler, takes an independent reference on the finished fence (standing in for a userspace sync_file), lets the job finish, frees the scheduler, and then queries the timeline name through dma_fence_timeline_name().
Without the fix get_timeline_name() dereferences fence->sched of the freed scheduler and KASAN reports a slab-use-after-free read in drm_sched_fence_get_timeline_name(); with the fix the name was cached at init and the freed scheduler is never touched. The test needs no hardware - it exercises the drm_sched core through the existing mock scheduler under KASAN. Per review it lives in a new tests_integration.c rather than in tests_basic.c, since it is about the scheduler's interaction with the dma-fence API rather than scheduler behaviour in isolation. Signed-off-by: Jonghyuk Kim(MalHyuk) <[email protected]> --- drivers/gpu/drm/scheduler/tests/Makefile | 1 + .../drm/scheduler/tests/tests_integration.c | 88 +++++++++++++++++++ 2 files changed, 89 insertions(+) create mode 100644 drivers/gpu/drm/scheduler/tests/tests_integration.c diff --git a/drivers/gpu/drm/scheduler/tests/Makefile b/drivers/gpu/drm/scheduler/tests/Makefile index 9ec185fbbc15..10abe07c06d2 100644 --- a/drivers/gpu/drm/scheduler/tests/Makefile +++ b/drivers/gpu/drm/scheduler/tests/Makefile @@ -3,6 +3,7 @@ drm-sched-tests-y := \ mock_scheduler.o \ tests_basic.o \ + tests_integration.o \ tests_scheduler.o obj-$(CONFIG_DRM_SCHED_KUNIT_TEST) += drm-sched-tests.o diff --git a/drivers/gpu/drm/scheduler/tests/tests_integration.c b/drivers/gpu/drm/scheduler/tests/tests_integration.c new file mode 100644 index 000000000000..4a2d5571440d --- /dev/null +++ b/drivers/gpu/drm/scheduler/tests/tests_integration.c @@ -0,0 +1,88 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <linux/dma-fence.h> +#include <linux/rcupdate.h> + +#include "sched_tests.h" + +/* + * Integration-style regression tests that exercise the interaction between the + * DRM scheduler and the dma-fence API, rather than scheduler behaviour in + * isolation. + */ + +/* + * Reproduce the drm_sched_fence timeline-name use-after-free. + * + * drm_sched_fence_get_timeline_name() used to dereference fence->sched->name. + * A driver may free a per-context/per-queue/per-VM drm_gpu_scheduler while + * userspace still holds the exported ->finished fence (via sync_file / + * drm_syncobj). Querying the timeline name afterwards must not touch the freed + * scheduler. + * + * Without the fix this reads fence->sched->name from freed slab memory and + * KASAN reports a slab-use-after-free in drm_sched_fence_get_timeline_name(); + * with the fix the name is cached at init and the freed scheduler is never + * dereferenced. Same class as CVE-2025-38703 (drm/xe) and CVE-2025-71302 + * (drm/panthor). + */ +static void drm_sched_dma_fence_uaf(struct kunit *test) +{ + struct drm_mock_sched_entity *entity; + struct drm_mock_scheduler *sched; + struct drm_mock_sched_job *job; + struct dma_fence *finished; + const char __rcu *name; + bool done; + + sched = drm_mock_sched_new(test, MAX_SCHEDULE_TIMEOUT); + entity = drm_mock_sched_entity_new(test, DRM_SCHED_PRIORITY_NORMAL, + sched); + job = drm_mock_sched_job_new(test, entity); + + /* The s_fence is only created by drm_sched_job_arm(). */ + drm_mock_sched_job_submit(job); + + /* Independent reference on the finished fence == userspace sync_file. */ + finished = dma_fence_get(&job->base.s_fence->finished); + + /* Let the job get scheduled (hw fence created), then signal + finish. */ + done = drm_mock_sched_job_wait_scheduled(job, HZ); + KUNIT_ASSERT_TRUE(test, done); + drm_mock_sched_advance(sched, 1); + done = drm_mock_sched_job_wait_finished(job, HZ); + KUNIT_ASSERT_TRUE(test, done); + + /* + * Free the per-context scheduler while the finished fence is held. + * kunit_kfree() releases the backing memory immediately (rather than at + * test teardown) so that fence->sched becomes a dangling pointer now. + */ + drm_mock_sched_entity_free(entity); + drm_mock_sched_fini(sched); + kunit_kfree(test, sched); + + /* + * Query the timeline name of the now-stale fence. With the fix the name + * was cached at init, so the freed scheduler is not dereferenced; + * without it this is a use-after-free read of the freed scheduler. + */ + rcu_read_lock(); + name = dma_fence_timeline_name(finished); + KUNIT_EXPECT_NOT_NULL(test, name); + rcu_read_unlock(); + + dma_fence_put(finished); +} + +static struct kunit_case drm_sched_dma_fence_tests[] = { + KUNIT_CASE(drm_sched_dma_fence_uaf), + {} +}; + +static struct kunit_suite drm_sched_dma_fence = { + .name = "drm_sched_dma_fence_uaf_tests", + .test_cases = drm_sched_dma_fence_tests, +}; + +kunit_test_suite(drm_sched_dma_fence); -- 2.43.0
