Add a KUnit test that reproduces the use-after-free fixed by the previous patch. It holds a reference on a job's finished drm_sched_fence (standing in for a userspace sync_file), frees the mock scheduler, then calls get_timeline_name(). Before the fix this triggers a KASAN slab-use-after-free read of the freed scheduler; after it the test passes.
The test needs no hardware - it exercises the drm_sched core through the existing mock scheduler under KASAN. Signed-off-by: Jonghyuk Kim(MalHyuk) <[email protected]> --- drivers/gpu/drm/scheduler/tests/tests_basic.c | 65 ++++++++++++++++++- 1 file changed, 64 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/scheduler/tests/tests_basic.c b/drivers/gpu/drm/scheduler/tests/tests_basic.c index a5a5a35a87b0..2c6744b58f04 100644 --- a/drivers/gpu/drm/scheduler/tests/tests_basic.c +++ b/drivers/gpu/drm/scheduler/tests/tests_basic.c @@ -555,9 +555,72 @@ static struct kunit_suite drm_sched_credits = { .test_cases = drm_sched_credits_tests, }; +/* + * Reproduce the drm_sched_fence get_timeline_name() lifetime bug. + * + * drm_sched_fence_get_timeline_name() dereferences fence->sched->name, and the + * drm_sched_fence ops keep .release set, so the fence is NOT ops-detached on + * signal (unlike stub fences). A driver that frees a per-context + * drm_gpu_scheduler while userspace still holds the exported ->finished fence + * (via sync_file / drm_syncobj) leaves fence->sched dangling; reading the + * timeline name then touches freed slab memory (arbitrary-read once the slab is + * re-sprayed). Confirmed instances: amdxdna, nouveau, msm. Same class as + * CVE-2025-38703 (xe) and CVE-2025-71302 (panthor). KASAN reports a + * slab-use-after-free READ in drm_sched_fence_get_timeline_name. + */ +static void drm_sched_fence_get_timeline_name_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 *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); + + /* Arm + submit first; 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 picked up (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. */ + drm_mock_sched_entity_free(entity); + drm_mock_sched_fini(sched); + kunit_kfree(test, sched); + + /* UAF read: fence->sched->name is read from the freed scheduler. */ + name = finished->ops->get_timeline_name(finished); + kunit_info(test, "get_timeline_name() on stale fence returned %p\n", name); + + dma_fence_put(finished); +} + +static struct kunit_case drm_sched_fence_uaf_tests[] = { + KUNIT_CASE(drm_sched_fence_get_timeline_name_uaf), + {} +}; + +static struct kunit_suite drm_sched_fence_uaf = { + .name = "drm_sched_fence_uaf_tests", + .test_cases = drm_sched_fence_uaf_tests, +}; + kunit_test_suites(&drm_sched_basic, &drm_sched_timeout, &drm_sched_cancel, &drm_sched_priority, &drm_sched_modify_sched, - &drm_sched_credits); + &drm_sched_credits, + &drm_sched_fence_uaf); -- 2.43.0
