From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793882797; b=geBgdZK0FyK048J0kPMqpFTPHGFgtV4b1RWuBTXgSg/4jsmHWeFxdZ1cdM20QmgqHgoq 4NX9V6sqQh6CRzqfiXLxUzQUXGlxe1TLL0NlICJcQIE2vcnBXRl0oNTETb9h9l5e6tBGo fVyoN9CXiWHA+9xFcU8BlFtcLcdy43WtrLM+zkGvlz/PlaKc2g3/VY0Zjf5exqtt00xbr AwppEd1Xmw+HpOXeeflqmjvSpyFPRMlt7w2Dc9WZF3OoC+f0boLL7lc/1Vwxl1f77FfI8 +KPaEwqb/WI0zTCgTVhU55Sj1ZmsoCFun2GNjU5KDor4Cdpgto3XKslDuHvySP2HU5A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793882797; h=Received:DKIM-Signature:Date:From:To:List-Id:Cc:Subject:Message-ID: X-Mailer:References:MIME-Version:Content-Type:Content-Disposition: In-Reply-To; bh=qR+ajvSYIWPcrZNdjwbZ50re504SAD6q3ySr9SMHBx8=; b=UZgoF8fM48sTpWnkysXNGb5/T2OHlEGQaTWDHEw42gXye1S5W1HXiRPQ4gZwZ+AJQrJ7 vqaJ+nWSjVd/I0PNEYhEIADQb5lMRBuLy4yCOYai7vZaKjBIqALMNtMRLaZMI7tB9Xc1f htrftL9XV5wuChrMXrgo1reTaWyWl/9spiK0EdmcYLHSjf+BaDWuyD8akw4FoHNBx+RHr 1B84Cu8Ba36YFsHDgD4BcesYN9Jfvp0ESNPvMN2TiRz60oS+vRCTGs3xSZsQuz9MUV8CQ SBpOfY+Nni+uLGM9MT0DLjk66GLUA8sqRR34xMgsVkjtJs2gPOn4NMOEHN8qLKJPEUg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ZZxMliIS; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1BF93606EEA9; Thu, 5 Nov 2026 12:46:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ZZxMliIS Received: by smtp.kernel.org (Postfix) with ESMTPSA id 100191F000C1; Thu, 5 Nov 2026 12:46:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793882796; bh=qR+ajvSYIWPcrZNdjwbZ50re504SAD6q3ySr9SMHBx8=; h=Date:From:To:List-Id:Cc:Subject:References:In-Reply-To; b=ZZxMliISmCl/Tp4L06tvt5/sKFhrPNo2vAlfg9fO9139UMkY6UslmksHQv4Seldj7 vRmYkaERO9yABDNP9h0dWn6OBbdhbBuLJcMQfAIkycmLwfDPT4octgL9d6tOIR/o7F 4e3NtvSNQiWUegIAsN0E3XpzvsYgCewXmh7/a1TLY4W4RkgYxD7NAQ4voNEgNoMB8C +1wh1R3JWMQslLsqkJ8TqWb4ft3F+Z7mdYzMJDMoFM0JTB0rXGtQINavj8/iQVOdxP 3q2s49ytUZaiz2MraBIi+Gy2PfMElAuStZLCHvAjP6/L8zFgyTVd3uyeKp9r96z9Du E3a1IwOnSGFhA== Date: Thu, 5 Nov 2026 13:46:29 +0100 From: Alejandro Colomar To: linux-hardening@vger.kernel.org Cc: Alejandro Colomar , alx+linux-hardening@kernel.org, Andreas Schwab , Andy Shevchenko , Bartosz Golaszewski , Daniel Scally , Danilo Krummrich , Greg Kroah-Hartman , Hans Verkuil , Heikki Krogerus , Joe Perches , Johan Hovold , Kees Cook , Laurent Pinchart , Len Brown , Linus Torvalds , Linus Walleij , Namhyung Kim , "Rafael J. Wysocki" , Rob Herring , Sakari Ailus , Saravana Kannan , Steven Rostedt , Tom Zanussi , linux-acpi@vger.kernel.org, driver-core@lists.linux.dev, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-gpio@vger.kernel.org, Bartosz Golaszewski Subject: [PATCH v2 1/2] string: Add strprefix(), and deprecate str_has_prefix() Message-ID: X-Mailer: git-send-email 2.55.0 References: X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="qn7iw7mespqvynf7" Content-Disposition: inline In-Reply-To: --qn7iw7mespqvynf7 Content-Type: text/plain; protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable From: Alejandro Colomar To: linux-hardening@vger.kernel.org List-Id: Cc: Alejandro Colomar , alx+linux-hardening@kernel.org, Andreas Schwab , Andy Shevchenko , Bartosz Golaszewski , Daniel Scally , Danilo Krummrich , Greg Kroah-Hartman , Hans Verkuil , Heikki Krogerus , Joe Perches , Johan Hovold , Kees Cook , Laurent Pinchart , Len Brown , Linus Torvalds , Linus Walleij , Namhyung Kim , "Rafael J. Wysocki" , Rob Herring , Sakari Ailus , Saravana Kannan , Steven Rostedt , Tom Zanussi , linux-acpi@vger.kernel.org, driver-core@lists.linux.dev, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-gpio@vger.kernel.org, Bartosz Golaszewski Subject: [PATCH v2 1/2] string: Add strprefix(), and deprecate str_has_prefix() Message-ID: References: MIME-Version: 1.0 In-Reply-To: As Bartosz reported, str_has_prefix() has a bug: it can't differentiate between an empty prefix matching an empty string from a non-matching prefix. This is a fundamental design flaw in this API, and not something that can be fixed. As always, this is a consequence of choosing sizes instead of pointers. Sizes are often the wrong choice. In this specific case, pointers are more capable of differentiating these cases, as NULL is a special sentinel value that doesn't need to overload a valid value. Let's implement strprefix(), a function that returns a pointer right after the prefix if found, and a null pointer if not found. We'll slowly migrate existing code from str_has_prefix() to strprefix(). Reported-by: Bartosz Golaszewski Cc: Andy Shevchenko Signed-off-by: Alejandro Colomar --- include/linux/string.h | 19 ++++++++++++++++++- lib/tests/string_kunit.c | 9 +++++++++ 2 files changed, 27 insertions(+), 1 deletion(-) diff --git a/include/linux/string.h b/include/linux/string.h index 6cb5cdd01158..0397e630bdc8 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -545,16 +545,33 @@ void memcpy_and_pad(void *dest, size_t dest_len, cons= t void *src, size_t count, sizeof(*(obj)) - offsetof(typeof(*(obj)), member)); \ }) =20 +/** + * strprefix - string prefix + * @s: The string to be tested + * @prefix: The string to see if @s starts with + * + * Returns: + * * @s+strlen(@prefix) if @s starts with @prefix + * * NULL if @s does not start with @prefix + */ +static __always_inline char *strprefix(const char *s, const char *prefix) +{ + size_t len =3D strlen(prefix); + return strncmp(s, prefix, len) =3D=3D 0 ? (char *) s + len : NULL; +} + /** * str_has_prefix - Test if a string has a given prefix * @str: The string to test * @prefix: The string to see if @str starts with * + * DEPRECATED: Use strprefix() + * * A common way to test a prefix of a string is to do: * strncmp(str, prefix, sizeof(prefix) - 1) * * But this can lead to bugs due to typos, or if prefix is a pointer - * and not a constant. Instead use str_has_prefix(). + * and not a constant. Instead use strprefix(). * * Returns: * * strlen(@prefix) if @str starts with @prefix diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c index 0819ace5b027..73d2614b1474 100644 --- a/lib/tests/string_kunit.c +++ b/lib/tests/string_kunit.c @@ -287,6 +287,14 @@ static void string_test_strspn(struct kunit *test) } } =20 +static void string_test_strprefix(struct kunit *test) +{ + KUNIT_ASSERT_EQ(test, 0, strcmp(strprefix("foobar", "foo"), "bar")); + KUNIT_ASSERT_EQ(test, 0, strcmp(strprefix("foobar", ""), "foobar")); + KUNIT_ASSERT_EQ(test, 0, strcmp(strprefix("foobar", "foobar"), "")); + KUNIT_ASSERT_NULL(test, strprefix("foobar", "bar")); +} + static char strcmp_buffer1[STRCMP_LARGE_BUF_LEN]; static char strcmp_buffer2[STRCMP_LARGE_BUF_LEN]; =20 @@ -891,6 +899,7 @@ static struct kunit_case string_test_cases[] =3D { KUNIT_CASE(string_test_strnchr), KUNIT_CASE(string_test_strrchr), KUNIT_CASE(string_test_strspn), + KUNIT_CASE(string_test_strprefix), KUNIT_CASE(string_test_strcmp), KUNIT_CASE(string_test_strcmp_long_strings), KUNIT_CASE(string_test_strncmp), --=20 2.55.0 --qn7iw7mespqvynf7 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEES7Jt9u9GbmlWADAi64mZXMKQwqkFAmrseqUACgkQ64mZXMKQ wqmE+RAAi//xNeKO6CmsOrB3NIvDBoX24bbY3uNB1l7M0K0l/nlKlGL9O90gBn4W o2PXYR9FBlFtm7UpiE3erJ2CRuDEFMxE4Cpkrkjq1shHK0TNDM610K9wOxkRcPYO 4eWMlqPUHp4GQck96BgTD+D6XSbahqhHGhzwcda9OzTG/utn2mRMiKLfpQ0JKl5z bsYI7V5iY9z1MqIEv1yHA9h9rzFvZrJPsE/IGuYvF9+8iMzAYpy9GK7+VLljmPYQ OO17C8dKQ2rS7HF8C1SEyevg2Xad9ACHzsXqqqVGZ6lBMEMX33jPtMhKtkPNlGZ6 FIHG03WpI7Sf1267kwQQMq3ovtq/lMKdoYpfiqkolAsBjoDO8+8CrU7N4SfqyNJV KtCx4bujHxHrI6Pg3p9Jo65tQKFeE+wuJEvrCBRhFCvOvA3OywWyUsHl5YWAnbHd kKY1k++YN3UiRRX9n701F0DDsZ3VUcdLD+vtyBPZPbWFK0SN+0SptSz1rGzv3u/E kOAdr0/gue4WGhprVoOTFk4J0Di/EtoDX2wA9ztY6lC8ZBUZ5YCZ4sLA1CnJ42FF m/ZCAdAIUHed6nNA5mfYCD/9GvtdeY+fifDvny9O01Rn0C/zNUaN7S1gULW6oXil Jkvh+AwDpRSJJ1yL/XUiqUn6Vf67Eq0TSDGPQWqrpcOX9UcRHU8= =VU/x -----END PGP SIGNATURE----- --qn7iw7mespqvynf7--