Re: [PATCH 3/9] string: Add Kunit tests for strcat() family

[Alexander Potapenko]

On Fri, Apr 7, 2023 at 1:07 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> 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) == 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?
>
> 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 == ""
> strncat(dest, "four", 4);
> // dest == "four"
> strncat(dest, "four", 4);
> // dest == "fourfour"
>
> strncat's "n" is how much to reach from source -- dest will always be
> terminated.
>
> --
> Kees Cook



-- 
Alexander Potapenko
Software Engineer

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