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From:   Alexander Potapenko <glider@google.com>
Date:   Wed, 12 Apr 2023 14:34:00 +0200
Message-ID: <CAG_fn=VfHU7-ixnxXN=34nvnNyvfZ2QVgOVWfvj7AxKZR706bQ@mail.gmail.com>
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>,
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        "Masami Hiramatsu (Google)" <mhiramat@kernel.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
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        Daniel Latypov <dlatypov@google.com>,
        =?UTF-8?B?Sm9zw6kgRXhww7NzaXRv?= <jose.exposito89@gmail.com>,
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On Fri, Apr 7, 2023 at 1:07=E2=80=AFAM Kees Cook <keescook@chromium.org> wr=
ote:
>
> On Thu, Apr 06, 2023 at 11:11:09AM +0200, Alexander Potapenko wrote:
> > > +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) =3D=3D dest);
> > > +       KUNIT_EXPECT_STREQ(test, dest, "");
> > > +       /* Empty copy of size 1 does nothing too. */
> > > +       KUNIT_EXPECT_TRUE(test, strncat(dest, "", 1) =3D=3D dest);
> > > +       KUNIT_EXPECT_STREQ(test, dest, "");
> > > +       /* Copy of max 0 characters should do nothing. */
> > > +       KUNIT_EXPECT_TRUE(test, strncat(dest, "asdf", 0) =3D=3D dest)=
;
> > > +       KUNIT_EXPECT_STREQ(test, dest, "");
> > > +
> > > +       /* 4 characters copied in, even if max is 8. */
> > > +       KUNIT_EXPECT_TRUE(test, strncat(dest, "four\000123", 8) =3D=
=3D 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?
>
> I think I don't understand what state you want to test for? The line
> above (STREQ is checking dest is "four". Maybe I should check for
> dest[6] being 0 as well as dest[5]. But if that's not what you mean, I'm
> not sure. Is it something here:

Sorry, not sure why I wrote "strncat" here, I was thinking about
strncpy, which is handled in a different patch.
Please disregard.

> char dest[16];
> memset(dest, 0, sizeof(dest));
> // dest =3D=3D ""
> strncat(dest, "four", 4);
> // dest =3D=3D "four"
> strncat(dest, "four", 4);
> // dest =3D=3D "fourfour"
>
> strncat's "n" is how much to reach from source -- dest will always be
> terminated.
>
> --
> Kees Cook


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Alexander Potapenko
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