Re: [PATCH v2 1/3] kunit: fix UAF when run kfence test case test_gfpzero

[Marco Elver]

On Wed, 9 Mar 2022 at 09:19, 'Peng Liu' via kasan-dev
<kasan-dev@xxxxxxxxxxxxxxxx> wrote:
>
> 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.
>
> Signed-off-by: Peng Liu <liupeng256@xxxxxxxxxx>

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

Also Cc'ing more KUnit folks to double-check this is the right solution.

> ---
>  lib/kunit/try-catch.c   | 1 +
>  mm/kfence/kfence_test.c | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/kunit/try-catch.c b/lib/kunit/try-catch.c
> index be38a2c5ecc2..6b3d4db94077 100644
> --- a/lib/kunit/try-catch.c
> +++ b/lib/kunit/try-catch.c
> @@ -78,6 +78,7 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
>         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;
> diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
> index 50dbb815a2a8..caed6b4eba94 100644
> --- a/mm/kfence/kfence_test.c
> +++ b/mm/kfence/kfence_test.c
> @@ -623,7 +623,7 @@ static void test_gfpzero(struct kunit *test)
>                         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;
>                 }
> --
> 2.18.0.huawei.25
>
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