linux-kernel - Re: [PATCH 3/4] selftests/memfd: add tests for F_SEAL

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Date:   Thu, 7 Apr 2022 14:00:32 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Daniel Verkamp <dverkamp@...omium.org>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Mattias Nissler <mnissler@...omium.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 3/4] selftests/memfd: add tests for F_SEAL_EXEC

On 4/1/22 4:08 PM, Daniel Verkamp wrote:
> Basic tests to ensure that user/group/other execute bits cannot be
> changed after applying F_SEAL_EXEC to a memfd.
> 
> Signed-off-by: Daniel Verkamp <dverkamp@...omium.org>
> ---
>   tools/testing/selftests/memfd/memfd_test.c | 80 ++++++++++++++++++++++
>   1 file changed, 80 insertions(+)
> 
> diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
> index 94df2692e6e4..fdb0e46e9df9 100644
> --- a/tools/testing/selftests/memfd/memfd_test.c
> +++ b/tools/testing/selftests/memfd/memfd_test.c
> @@ -28,6 +28,10 @@
>   #define MFD_DEF_SIZE 8192
>   #define STACK_SIZE 65536
>   
> +#ifndef F_SEAL_EXEC
> +#define F_SEAL_EXEC	0x0020
> +#endif
> +
>   /*
>    * Default is not to test hugetlbfs
>    */
> @@ -594,6 +598,48 @@ static void mfd_fail_grow_write(int fd)
>   	}
>   }
>   
> +static void mfd_assert_mode(int fd, int mode)
> +{
> +	struct stat st;
> +
> +	if (fstat(fd, &st) < 0) {
> +		printf("fstat(%d) failed: %m\n", fd);

Let's print the filename here - just printing fd isn't useful.

> +		abort();
> +	} else if ((st.st_mode & 07777) != mode) {
> +		printf("wrong file mode 0%04o, but expected 0%04o\n",
> +		       (int)st.st_mode & 07777, mode);

This one doesn't even print fd - same comment here about filename.

> +		abort();
> +	}
> +}
> +
> +static void mfd_assert_chmod(int fd, int mode)
> +{
> +	if (fchmod(fd, mode) < 0) {
> +		printf("fchmod(0%04o) failed: %m\n", mode);

Same here.

> +		abort();
> +	}
> +
> +	mfd_assert_mode(fd, mode);
> +}
> +
> +static void mfd_fail_chmod(int fd, int mode)
> +{
> +	struct stat st;
> +
> +	if (fstat(fd, &st) < 0) {
> +		printf("fstat(%d) failed: %m\n", fd);

Same comment about filename

> +		abort();
> +	}
> +
> +	if (fchmod(fd, mode) == 0) {
> +		printf("fchmod(0%04o) didn't fail as expected\n");

Same comment about filename

> +		abort();
> +	}
> +
> +	/* verify that file mode bits did not change */
> +	mfd_assert_mode(fd, st.st_mode & 07777);
> +}
> +
>   static int idle_thread_fn(void *arg)
>   {
>   	sigset_t set;
> @@ -880,6 +926,39 @@ static void test_seal_resize(void)
>   	close(fd);
>   }
>   
> +/*
> + * Test SEAL_EXEC
> + * Test that chmod() cannot change x bits after sealing
> + */
> +static void test_seal_exec(void)
> +{
> +	int fd;
> +
> +	printf("%s SEAL-EXEC\n", memfd_str);
> +
> +	fd = mfd_assert_new("kern_memfd_seal_exec",
> +			    mfd_def_size,
> +			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
> +
> +	mfd_assert_mode(fd, 0777);
> +
> +	mfd_assert_chmod(fd, 0644);
> +
> +	mfd_assert_has_seals(fd, 0);
> +	mfd_assert_add_seals(fd, F_SEAL_EXEC);
> +	mfd_assert_has_seals(fd, F_SEAL_EXEC);
> +
> +	mfd_assert_chmod(fd, 0600);
> +	mfd_fail_chmod(fd, 0777);
> +	mfd_fail_chmod(fd, 0670);
> +	mfd_fail_chmod(fd, 0605);
> +	mfd_fail_chmod(fd, 0700);
> +	mfd_fail_chmod(fd, 0100);
> +	mfd_assert_chmod(fd, 0666);
> +
> +	close(fd);
> +}
> +
>   /*
>    * Test sharing via dup()
>    * Test that seals are shared between dupped FDs and they're all equal.
> @@ -1059,6 +1138,7 @@ int main(int argc, char **argv)
>   	test_seal_shrink();
>   	test_seal_grow();
>   	test_seal_resize();
> +	test_seal_exec();
>   
>   	test_share_dup("SHARE-DUP", "");
>   	test_share_mmap("SHARE-MMAP", "");
> 

The rest looks good.

thanks,
-- Shuah