linux-kernel - Re: [PATCH 4/4] selftests/memfd: add tests for MFD

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Date:   Thu, 28 Jul 2022 23:29:40 -0700
From:   Jeff Xu <jeffxu@...gle.com>
To:     skhan@...uxfoundation.org
Cc:     akpm@...ux-foundation.org, dmitry.torokhov@...il.com,
        dverkamp@...omium.org, hughd@...gle.com, jorgelo@...omium.org,
        keescook@...omium.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        mnissler@...omium.org
Subject: Re: [PATCH 4/4] selftests/memfd: add tests for MFD_NOEXEC

> > + /* Create with NOEXEC and ALLOW_SEALING */
> > + fd = mfd_assert_new("kern_memfd_noexec",
> > +    mfd_def_size,
> > +    MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_NOEXEC);


> Don't we need to check fd here?


mfd_assert_new will abort() if fd is not valid, so we don't check fd here.

Jeff


On Thu, Jul 28, 2022 at 11:15 PM Jeff Xu <jeffxu@...gle.com> wrote:
>
> From: Daniel Verkamp <dverkamp@...omium.org>
>
> Tests that ensure MFD_NOEXEC memfds have the appropriate mode bits and
> cannot be chmod-ed into being executable.
>
> Co-developed-by: Jeff Xu <jeffxu@...gle.com>
> Signed-off-by: Jeff Xu <jeffxu@...gle.com>
> Signed-off-by: Daniel Verkamp <dverkamp@...omium.org>
> ---
>  tools/testing/selftests/memfd/memfd_test.c | 34 ++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
>
> diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
> index 1d7e7b36bbdd..4906f778564e 100644
> --- a/tools/testing/selftests/memfd/memfd_test.c
> +++ b/tools/testing/selftests/memfd/memfd_test.c
> @@ -36,6 +36,10 @@
>  #define MAX_PATH 256
>  #endif
>
> +#ifndef MFD_NOEXEC
> +#define MFD_NOEXEC     0x0008U
> +#endif
> +
>  /*
>   * Default is not to test hugetlbfs
>   */
> @@ -1006,6 +1010,35 @@ static void test_seal_exec(void)
>         close(fd);
>  }
>
> +/*
> + * Test memfd_create with MFD_NOEXEC flag
> + * Test that MFD_NOEXEC applies F_SEAL_EXEC and prevents change of exec bits
> + */
> +static void test_noexec(void)
> +{
> +       int fd;
> +
> +       printf("%s NOEXEC\n", memfd_str);
> +
> +       /* Create with NOEXEC and ALLOW_SEALING */
> +       fd = mfd_assert_new("kern_memfd_noexec",
> +                           mfd_def_size,
> +                           MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_NOEXEC);
> +       mfd_assert_mode(fd, 0666);
> +       mfd_assert_has_seals(fd, F_SEAL_EXEC);
> +       mfd_fail_chmod(fd, 0777);
> +       close(fd);
> +
> +       /* Create with NOEXEC but without ALLOW_SEALING */
> +       fd = mfd_assert_new("kern_memfd_noexec",
> +                           mfd_def_size,
> +                           MFD_CLOEXEC | MFD_NOEXEC);
> +       mfd_assert_mode(fd, 0666);
> +       mfd_assert_has_seals(fd, F_SEAL_EXEC | F_SEAL_SEAL);
> +       mfd_fail_chmod(fd, 0777);
> +       close(fd);
> +}
> +
>  /*
>   * Test sharing via dup()
>   * Test that seals are shared between dupped FDs and they're all equal.
> @@ -1179,6 +1212,7 @@ int main(int argc, char **argv)
>
>         test_create();
>         test_basic();
> +       test_noexec();
>
>         test_seal_write();
>         test_seal_future_write();
> --
> 2.37.1.455.g008518b4e5-goog
>