From: Peng Liu <liupeng256@xxxxxxxxxx> Subject: kunit: fix UAF when run kfence test case test_gfpzero Patch series "kunit: fix a UAF bug and do some optimization", v2. This series is to fix UAF (use after free) when running kfence test case test_gfpzero, which is time costly. This UAF bug can be easily triggered by setting CONFIG_KFENCE_NUM_OBJECTS = 65535. Furthermore, some optimization for kunit tests has been done. This patch (of 3): Kunit will create a new thread to run an actual test case, and the main process will wait for the completion of the actual test thread until overtime. The variable "struct kunit test" has local property in function kunit_try_catch_run, and will be used in the test case thread. Task kunit_try_catch_run will free "struct kunit test" when kunit runs overtime, but the actual test case is still run and an UAF bug will be triggered. The above problem has been both observed in a physical machine and qemu platform when running kfence kunit tests. The problem can be triggered when setting CONFIG_KFENCE_NUM_OBJECTS = 65535. Under this setting, the test case test_gfpzero will cost hours and kunit will run to overtime. The follows show the panic log. BUG: unable to handle page fault for address: ffffffff82d882e9 Call Trace: kunit_log_append+0x58/0xd0 ... test_alloc.constprop.0.cold+0x6b/0x8a [kfence_test] test_gfpzero.cold+0x61/0x8ab [kfence_test] kunit_try_run_case+0x4c/0x70 kunit_generic_run_threadfn_adapter+0x11/0x20 kthread+0x166/0x190 ret_from_fork+0x22/0x30 Kernel panic - not syncing: Fatal exception Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 To solve this problem, the test case thread should be stopped when the kunit frame runs overtime. The stop signal will send in function kunit_try_catch_run, and test_gfpzero will handle it. Link: https://lkml.kernel.org/r/20220309083753.1561921-1-liupeng256@xxxxxxxxxx Link: https://lkml.kernel.org/r/20220309083753.1561921-2-liupeng256@xxxxxxxxxx Signed-off-by: Peng Liu <liupeng256@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Reviewed-by: Brendan Higgins <brendanhiggins@xxxxxxxxxx> Tested-by: Brendan Higgins <brendanhiggins@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Wang Kefeng <wangkefeng.wang@xxxxxxxxxx> Cc: Daniel Latypov <dlatypov@xxxxxxxxxx> Cc: David Gow <davidgow@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/kunit/try-catch.c | 1 + mm/kfence/kfence_test.c | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-) --- a/lib/kunit/try-catch.c~kunit-fix-uaf-when-run-kfence-test-case-test_gfpzero +++ a/lib/kunit/try-catch.c @@ -78,6 +78,7 @@ void kunit_try_catch_run(struct kunit_tr if (time_remaining == 0) { kunit_err(test, "try timed out\n"); try_catch->try_result = -ETIMEDOUT; + kthread_stop(task_struct); } exit_code = try_catch->try_result; --- a/mm/kfence/kfence_test.c~kunit-fix-uaf-when-run-kfence-test-case-test_gfpzero +++ a/mm/kfence/kfence_test.c @@ -623,7 +623,7 @@ static void test_gfpzero(struct kunit *t break; test_free(buf2); - if (i == CONFIG_KFENCE_NUM_OBJECTS) { + if (kthread_should_stop() || (i == CONFIG_KFENCE_NUM_OBJECTS)) { kunit_warn(test, "giving up ... cannot get same object back\n"); return; } _
