Re: [PATCH v1 0/2] Add strprefix() and fix a bug with it

[Alejandro Colomar <alx+linux-hardening@kernel.org>]

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Hi Andy,

> Date: 2026-11-05 13:24:18+0200
> From: Andy Shevchenko <andy.shevchenko@gmail.com>
>
> On Thu, Nov 5, 2026 at 1:13 PM Alejandro Colomar <alx@kernel.org> wrote:
> >
> > str_has_prefix() is based on sizes and lengths, which means it must
> > overload the valid length 0 to mean not found.  This is a typical
> > consequence of choosing to design an API around sizes and lengths, and
> > vanishes when moving to pointer-based similar APIs.
> >
> > This patch set adds strprefix(), deprecates str_has_prefix(), and uses
> > strprefix() in one place to fix a bug reported by Bartosz.
> >
> > We can later work on replacing the other uses of str_has_prefix(), which
> > might hide similar bugs.
> >
> > Testing
> > ~~~~~~~
> >
> > I've built this patch set with 'allmodconfig'.  I've not run the
> > resulting kernel, though.
> 
> No, all lib/ new code should be accompanied with new (Kunit) test
> cases. Update the respective lib/tests/* for that or if not yet
> converted to Kunit something in lib/*test*.c

Thanks!  Does this sound good to you?

	diff --git i/lib/tests/string_kunit.c w/lib/tests/string_kunit.c
	index 0819ace5b027..702030dbb93b 100644
	--- i/lib/tests/string_kunit.c
	+++ w/lib/tests/string_kunit.c
	@@ -287,6 +287,14 @@ static void string_test_strspn(struct kunit *test)
		}
	 }
	 
	+static void string_test_strprefix(struct kunit *test)
	+{
	+       KUNIT_ASSERT_EQ(test, strcmp(strprefix("foobar", "foo"), "bar"), 0);
	+       KUNIT_ASSERT_EQ(test, strcmp(strprefix("foobar", ""), "foobar"), 0);
	+       KUNIT_ASSERT_EQ(test, strcmp(strprefix("foobar", "foobar"), ""), 0);
	+       KUNIT_ASSERT_NULL(test, strprefix("foobar", "bar"));
	+}
	+
	 static char strcmp_buffer1[STRCMP_LARGE_BUF_LEN];
	 static char strcmp_buffer2[STRCMP_LARGE_BUF_LEN];
	 

BTW, I don't see any existing tests of str_has_prefix() --the API I'm
replacing-- under lib/.

	$ grep -rn str_has_prefix lib/
	$ 


Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es>

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