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From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 6 Apr 2023 11:11:09 +0200
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Subject: Re: [PATCH 3/9] string: Add Kunit tests for strcat() family
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-hardening@vger.kernel.org, Kees Cook <kees@outflux.net>,
        Andy Shevchenko <andy@kernel.org>,
        Cezary Rojewski <cezary.rojewski@intel.com>,
        Puyou Lu <puyou.lu@gmail.com>, Mark Brown <broonie@kernel.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Brendan Higgins <brendan.higgins@linux.dev>,
        David Gow <davidgow@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Zhaoyang Huang <zhaoyang.huang@unisoc.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Miguel Ojeda <ojeda@kernel.org>,
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        Liam Howlett <liam.howlett@oracle.com>,
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        Sander Vanheule <sander@svanheule.net>,
        Eric Biggers <ebiggers@google.com>,
        "Masami Hiramatsu (Google)" <mhiramat@kernel.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Daniel Latypov <dlatypov@google.com>,
        =?UTF-8?B?Sm9zw6kgRXhww7NzaXRv?= <jose.exposito89@gmail.com>,
        linux-kernel@vger.kernel.org, kunit-dev@googlegroups.com
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> +static void strncat_test(struct kunit *test)
> +{
> +       char dest[8];
> +
> +       /* Destination is terminated. */
> +       memset(dest, 0, sizeof(dest));
> +       KUNIT_EXPECT_EQ(test, strlen(dest), 0);
> +       /* Empty copy of size 0 does nothing. */
> +       KUNIT_EXPECT_TRUE(test, strncat(dest, "", 0) == dest);
> +       KUNIT_EXPECT_STREQ(test, dest, "");
> +       /* Empty copy of size 1 does nothing too. */
> +       KUNIT_EXPECT_TRUE(test, strncat(dest, "", 1) == dest);
> +       KUNIT_EXPECT_STREQ(test, dest, "");
> +       /* Copy of max 0 characters should do nothing. */
> +       KUNIT_EXPECT_TRUE(test, strncat(dest, "asdf", 0) == dest);
> +       KUNIT_EXPECT_STREQ(test, dest, "");
> +
> +       /* 4 characters copied in, even if max is 8. */
> +       KUNIT_EXPECT_TRUE(test, strncat(dest, "four\000123", 8) == dest);
> +       KUNIT_EXPECT_STREQ(test, dest, "four");
> +       KUNIT_EXPECT_EQ(test, dest[5], '\0');

Maybe also add a test case for strncat(dest, "four", 4) that checks
that the fourth byte of dest is not 0?