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

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Date:   Thu, 10 Mar 2022 03:08:59 -0500
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Peng Liu <liupeng256@...wei.com>
Cc:     glider@...gle.com, elver@...gle.com, dvyukov@...gle.com,
        akpm@...ux-foundation.org, linux-kselftest@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        wangkefeng.wang@...wei.com
Subject: Re: [PATCH v2 1/3] kunit: fix UAF when run kfence test case test_gfpzero

On Wed, Mar 9, 2022 at 3:19 AM 'Peng Liu' via KUnit Development
<kunit-dev@...glegroups.com> 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@...wei.com>

Thanks for taking care of this.

Reviewed-by: Brendan Higgins <brendanhiggins@...gle.com>