Date:   Wed, 19 Oct 2022 12:39:06 +0800
From:   David Gow <davidgow@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Tobin C . Harding" <tobin@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] string: Convert strscpy() self-test to KUnit

On Tue, Oct 18, 2022 at 4:29 PM Kees Cook <keescook@...omium.org> wrote:
>
> Convert the strscpy() self-test to a KUnit test.
>
> Cc: David Gow <davidgow@...gle.com>
> Cc: Tobin C. Harding <tobin@...nel.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---

This looks fine, and works here, but I wonder if this is not better
suited to a parameterised test? That'd make it a bit easier to
interpret the results if only one or two of the "subtests" failed.

Basically, you give KUnit a test function alongside an array of data
(typically a struct), as well as a helper function to "describe" the
test, and KUnit will treat all executions of that function as
"subtests", and print out results.
The fat timestamp tests here are a good example:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/fat/fat_test.c#n23

Now, I suspect that this isn't an _ideal_ case for parameterised tests
(the individual cases are a little awkward to describe), so I'm okay
with it either way, but I think taking advantage of the parameterised
test infrastructure would be a little "cleaner" than the repeated
calls to the "tc" function.

Thoughts?

Regardless, this is:
Tested-by: David Gow <davidgow@...gle.com>

-- David

>  MAINTAINERS         |   1 +
>  lib/Kconfig.debug   |   8 ++-
>  lib/Makefile        |   2 +-
>  lib/strscpy_kunit.c | 129 +++++++++++++++++++++++++++++++++++++
>  lib/test_strscpy.c  | 150 --------------------------------------------
>  5 files changed, 136 insertions(+), 154 deletions(-)
>  create mode 100644 lib/strscpy_kunit.c
>  delete mode 100644 lib/test_strscpy.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 9dd8d74c4df0..232d78340d79 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8045,6 +8045,7 @@ T:        git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/har
>  F:     include/linux/fortify-string.h
>  F:     lib/fortify_kunit.c
>  F:     lib/memcpy_kunit.c
> +F:     lib/strscpy_kunit.c
>  F:     lib/test_fortify/*
>  F:     scripts/test_fortify.sh
>  K:     \b__NO_FORTIFY\b
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 3fc7abffc7aa..e0a4d52e434c 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -2215,9 +2215,6 @@ config STRING_SELFTEST
>  config TEST_STRING_HELPERS
>         tristate "Test functions located in the string_helpers module at runtime"
>
> -config TEST_STRSCPY
> -       tristate "Test strscpy*() family of functions at runtime"
> -
>  config TEST_KSTRTOX
>         tristate "Test kstrto*() family of functions at runtime"
>
> @@ -2583,6 +2580,11 @@ config HW_BREAKPOINT_KUNIT_TEST
>
>           If unsure, say N.
>
> +config STRSCPY_KUNIT_TEST
> +       tristate "Test strscpy*() family of functions at runtime" if !KUNIT_ALL_TESTS
> +       depends on KUNIT
> +       default KUNIT_ALL_TESTS
> +
>  config TEST_UDELAY
>         tristate "udelay test driver"
>         help
> diff --git a/lib/Makefile b/lib/Makefile
> index 161d6a724ff7..1905e5c26849 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -82,7 +82,6 @@ obj-$(CONFIG_TEST_DYNAMIC_DEBUG) += test_dynamic_debug.o
>  obj-$(CONFIG_TEST_PRINTF) += test_printf.o
>  obj-$(CONFIG_TEST_SCANF) += test_scanf.o
>  obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o
> -obj-$(CONFIG_TEST_STRSCPY) += test_strscpy.o
>  obj-$(CONFIG_TEST_UUID) += test_uuid.o
>  obj-$(CONFIG_TEST_XARRAY) += test_xarray.o
>  obj-$(CONFIG_TEST_PARMAN) += test_parman.o
> @@ -380,6 +379,7 @@ obj-$(CONFIG_OVERFLOW_KUNIT_TEST) += overflow_kunit.o
>  CFLAGS_stackinit_kunit.o += $(call cc-disable-warning, switch-unreachable)
>  obj-$(CONFIG_STACKINIT_KUNIT_TEST) += stackinit_kunit.o
>  obj-$(CONFIG_FORTIFY_KUNIT_TEST) += fortify_kunit.o
> +obj-$(CONFIG_STRSCPY_KUNIT_TEST) += strscpy_kunit.o
>
>  obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
>
> diff --git a/lib/strscpy_kunit.c b/lib/strscpy_kunit.c
> new file mode 100644
> index 000000000000..98523f828d3a
> --- /dev/null
> +++ b/lib/strscpy_kunit.c
> @@ -0,0 +1,129 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Kernel module for testing 'strscpy' family of functions.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <kunit/test.h>
> +#include <linux/string.h>
> +
> +/*
> + * tc() - Run a specific test case.
> + * @src: Source string, argument to strscpy_pad()
> + * @count: Size of destination buffer, argument to strscpy_pad()
> + * @expected: Expected return value from call to strscpy_pad()
> + * @terminator: 1 if there should be a terminating null byte 0 otherwise.
> + * @chars: Number of characters from the src string expected to be
> + *         written to the dst buffer.
> + * @pad: Number of pad characters expected (in the tail of dst buffer).
> + *       (@pad does not include the null terminator byte.)
> + *
> + * Calls strscpy_pad() and verifies the return value and state of the
> + * destination buffer after the call returns.
> + */
> +static void tc(struct kunit *test, char *src, int count, int expected,
> +              int chars, int terminator, int pad)
> +{
> +       int nr_bytes_poison;
> +       int max_expected;
> +       int max_count;
> +       int written;
> +       char buf[6];
> +       int index, i;
> +       const char POISON = 'z';
> +
> +       KUNIT_ASSERT_TRUE_MSG(test, src != NULL,
> +                             "null source string not supported");
> +
> +       memset(buf, POISON, sizeof(buf));
> +       /* Future proofing test suite, validate args */
> +       max_count = sizeof(buf) - 2; /* Space for null and to verify overflow */
> +       max_expected = count - 1;    /* Space for the null */
> +
> +       KUNIT_ASSERT_LE_MSG(test, count, max_count,
> +               "count (%d) is too big (%d) ... aborting", count, max_count);
> +       KUNIT_EXPECT_LE_MSG(test, expected, max_expected,
> +               "expected (%d) is bigger than can possibly be returned (%d)",
> +               expected, max_expected);
> +
> +       written = strscpy_pad(buf, src, count);
> +       KUNIT_ASSERT_EQ(test, written, expected);
> +
> +       if (count && written == -E2BIG) {
> +               KUNIT_ASSERT_EQ_MSG(test, 0, strncmp(buf, src, count - 1),
> +                       "buffer state invalid for -E2BIG");
> +               KUNIT_ASSERT_EQ_MSG(test, buf[count - 1], '\0',
> +                       "too big string is not null terminated correctly");
> +       }
> +
> +       for (i = 0; i < chars; i++)
> +               KUNIT_ASSERT_EQ_MSG(test, buf[i], src[i],
> +                       "buf[i]==%c != src[i]==%c", buf[i], src[i]);
> +
> +       if (terminator)
> +               KUNIT_ASSERT_EQ_MSG(test, buf[count - 1], '\0',
> +                       "string is not null terminated correctly");
> +
> +       for (i = 0; i < pad; i++) {
> +               index = chars + terminator + i;
> +               KUNIT_ASSERT_EQ_MSG(test, buf[index], '\0',
> +                       "padding missing at index: %d", i);
> +       }
> +
> +       nr_bytes_poison = sizeof(buf) - chars - terminator - pad;
> +       for (i = 0; i < nr_bytes_poison; i++) {
> +               index = sizeof(buf) - 1 - i; /* Check from the end back */
> +               KUNIT_ASSERT_EQ_MSG(test, buf[index], POISON,
> +                       "poison value missing at index: %d", i);
> +       }
> +}
> +
> +static void strscpy_test(struct kunit *test)
> +{
> +       /*
> +        * tc() uses a destination buffer of size 6 and needs at
> +        * least 2 characters spare (one for null and one to check for
> +        * overflow).  This means we should only call tc() with
> +        * strings up to a maximum of 4 characters long and 'count'
> +        * should not exceed 4.  To test with longer strings increase
> +        * the buffer size in tc().
> +        */
> +
> +       /* tc(test, src, count, expected, chars, terminator, pad) */
> +       tc(test, "a", 0, -E2BIG, 0, 0, 0);
> +       tc(test, "",  0, -E2BIG, 0, 0, 0);
> +
> +       tc(test, "a", 1, -E2BIG, 0, 1, 0);
> +       tc(test, "",  1, 0,      0, 1, 0);
> +
> +       tc(test, "ab", 2, -E2BIG, 1, 1, 0);
> +       tc(test, "a",  2, 1,      1, 1, 0);
> +       tc(test, "",   2, 0,      0, 1, 1);
> +
> +       tc(test, "abc", 3, -E2BIG, 2, 1, 0);
> +       tc(test, "ab",  3, 2,      2, 1, 0);
> +       tc(test, "a",   3, 1,      1, 1, 1);
> +       tc(test, "",    3, 0,      0, 1, 2);
> +
> +       tc(test, "abcd", 4, -E2BIG, 3, 1, 0);
> +       tc(test, "abc",  4, 3,      3, 1, 0);
> +       tc(test, "ab",   4, 2,      2, 1, 1);
> +       tc(test, "a",    4, 1,      1, 1, 2);
> +       tc(test, "",     4, 0,      0, 1, 3);
> +}
> +
> +static struct kunit_case strscpy_test_cases[] = {
> +       KUNIT_CASE(strscpy_test),
> +       {}
> +};
> +
> +static struct kunit_suite strscpy_test_suite = {
> +       .name = "strscpy",
> +       .test_cases = strscpy_test_cases,
> +};
> +
> +kunit_test_suite(strscpy_test_suite);
> +
> +MODULE_AUTHOR("Tobin C. Harding <tobin@...nel.org>");
> +MODULE_LICENSE("GPL");
> diff --git a/lib/test_strscpy.c b/lib/test_strscpy.c
> deleted file mode 100644
> index a827f94601f5..000000000000
> --- a/lib/test_strscpy.c
> +++ /dev/null
> @@ -1,150 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0+
> -
> -#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> -
> -#include <linux/string.h>
> -
> -#include "../tools/testing/selftests/kselftest_module.h"
> -
> -/*
> - * Kernel module for testing 'strscpy' family of functions.
> - */
> -
> -KSTM_MODULE_GLOBALS();
> -
> -/*
> - * tc() - Run a specific test case.
> - * @src: Source string, argument to strscpy_pad()
> - * @count: Size of destination buffer, argument to strscpy_pad()
> - * @expected: Expected return value from call to strscpy_pad()
> - * @terminator: 1 if there should be a terminating null byte 0 otherwise.
> - * @chars: Number of characters from the src string expected to be
> - *         written to the dst buffer.
> - * @pad: Number of pad characters expected (in the tail of dst buffer).
> - *       (@pad does not include the null terminator byte.)
> - *
> - * Calls strscpy_pad() and verifies the return value and state of the
> - * destination buffer after the call returns.
> - */
> -static int __init tc(char *src, int count, int expected,
> -                    int chars, int terminator, int pad)
> -{
> -       int nr_bytes_poison;
> -       int max_expected;
> -       int max_count;
> -       int written;
> -       char buf[6];
> -       int index, i;
> -       const char POISON = 'z';
> -
> -       total_tests++;
> -
> -       if (!src) {
> -               pr_err("null source string not supported\n");
> -               return -1;
> -       }
> -
> -       memset(buf, POISON, sizeof(buf));
> -       /* Future proofing test suite, validate args */
> -       max_count = sizeof(buf) - 2; /* Space for null and to verify overflow */
> -       max_expected = count - 1;    /* Space for the null */
> -       if (count > max_count) {
> -               pr_err("count (%d) is too big (%d) ... aborting", count, max_count);
> -               return -1;
> -       }
> -       if (expected > max_expected) {
> -               pr_warn("expected (%d) is bigger than can possibly be returned (%d)",
> -                       expected, max_expected);
> -       }
> -
> -       written = strscpy_pad(buf, src, count);
> -       if ((written) != (expected)) {
> -               pr_err("%d != %d (written, expected)\n", written, expected);
> -               goto fail;
> -       }
> -
> -       if (count && written == -E2BIG) {
> -               if (strncmp(buf, src, count - 1) != 0) {
> -                       pr_err("buffer state invalid for -E2BIG\n");
> -                       goto fail;
> -               }
> -               if (buf[count - 1] != '\0') {
> -                       pr_err("too big string is not null terminated correctly\n");
> -                       goto fail;
> -               }
> -       }
> -
> -       for (i = 0; i < chars; i++) {
> -               if (buf[i] != src[i]) {
> -                       pr_err("buf[i]==%c != src[i]==%c\n", buf[i], src[i]);
> -                       goto fail;
> -               }
> -       }
> -
> -       if (terminator) {
> -               if (buf[count - 1] != '\0') {
> -                       pr_err("string is not null terminated correctly\n");
> -                       goto fail;
> -               }
> -       }
> -
> -       for (i = 0; i < pad; i++) {
> -               index = chars + terminator + i;
> -               if (buf[index] != '\0') {
> -                       pr_err("padding missing at index: %d\n", i);
> -                       goto fail;
> -               }
> -       }
> -
> -       nr_bytes_poison = sizeof(buf) - chars - terminator - pad;
> -       for (i = 0; i < nr_bytes_poison; i++) {
> -               index = sizeof(buf) - 1 - i; /* Check from the end back */
> -               if (buf[index] != POISON) {
> -                       pr_err("poison value missing at index: %d\n", i);
> -                       goto fail;
> -               }
> -       }
> -
> -       return 0;
> -fail:
> -       failed_tests++;
> -       return -1;
> -}
> -
> -static void __init selftest(void)
> -{
> -       /*
> -        * tc() uses a destination buffer of size 6 and needs at
> -        * least 2 characters spare (one for null and one to check for
> -        * overflow).  This means we should only call tc() with
> -        * strings up to a maximum of 4 characters long and 'count'
> -        * should not exceed 4.  To test with longer strings increase
> -        * the buffer size in tc().
> -        */
> -
> -       /* tc(src, count, expected, chars, terminator, pad) */
> -       KSTM_CHECK_ZERO(tc("a", 0, -E2BIG, 0, 0, 0));
> -       KSTM_CHECK_ZERO(tc("", 0, -E2BIG, 0, 0, 0));
> -
> -       KSTM_CHECK_ZERO(tc("a", 1, -E2BIG, 0, 1, 0));
> -       KSTM_CHECK_ZERO(tc("", 1, 0, 0, 1, 0));
> -
> -       KSTM_CHECK_ZERO(tc("ab", 2, -E2BIG, 1, 1, 0));
> -       KSTM_CHECK_ZERO(tc("a", 2, 1, 1, 1, 0));
> -       KSTM_CHECK_ZERO(tc("", 2, 0, 0, 1, 1));
> -
> -       KSTM_CHECK_ZERO(tc("abc", 3, -E2BIG, 2, 1, 0));
> -       KSTM_CHECK_ZERO(tc("ab", 3, 2, 2, 1, 0));
> -       KSTM_CHECK_ZERO(tc("a", 3, 1, 1, 1, 1));
> -       KSTM_CHECK_ZERO(tc("", 3, 0, 0, 1, 2));
> -
> -       KSTM_CHECK_ZERO(tc("abcd", 4, -E2BIG, 3, 1, 0));
> -       KSTM_CHECK_ZERO(tc("abc", 4, 3, 3, 1, 0));
> -       KSTM_CHECK_ZERO(tc("ab", 4, 2, 2, 1, 1));
> -       KSTM_CHECK_ZERO(tc("a", 4, 1, 1, 1, 2));
> -       KSTM_CHECK_ZERO(tc("", 4, 0, 0, 1, 3));
> -}
> -
> -KSTM_MODULE_LOADERS(test_strscpy);
> -MODULE_AUTHOR("Tobin C. Harding <tobin@...nel.org>");
> -MODULE_LICENSE("GPL");
> --
> 2.34.1
>

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