linux-kernel - Re: [PATCH v4 01/10] string: provide strends()

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Message-ID: <202511171230.F83EE85D0@keescook>
Date: Mon, 17 Nov 2025 12:33:18 -0800
From: Kees Cook <kees@...nel.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Mika Westerberg <westeri@...nel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andy Shevchenko <andy@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Srinivas Kandagatla <srini@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	Alexey Klimov <alexey.klimov@...aro.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-gpio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-sound@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v4 01/10] string: provide strends()

On Wed, Nov 12, 2025 at 02:55:30PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> Implement a function for checking if a string ends with a different
> string and add its kunit test cases.
> 
> Acked-by: Linus Walleij <linus.walleij@...aro.org>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> ---
>  include/linux/string.h   | 18 ++++++++++++++++++
>  lib/tests/string_kunit.c | 13 +++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/include/linux/string.h b/include/linux/string.h
> index fdd3442c6bcbd786e177b6e87358e1065a0ffafc..929d05d1247c76eb9011fe34250b487834b2d3c9 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -562,4 +562,22 @@ static inline bool strstarts(const char *str, const char *prefix)
>  	return strncmp(str, prefix, strlen(prefix)) == 0;
>  }
>  
> +/**
> + * strends - Check if a string ends with another string.
> + * @str - NULL-terminated string to check against @suffix
> + * @suffix - NULL-terminated string defining the suffix to look for in @str
> + *
> + * Returns:
> + * True if @str ends with @suffix. False in all other cases.

Maybe added "empty strings never match"?

> + */
> +static inline bool strends(const char *str, const char *suffix)

These are required to be non-NULL, so we might want to consider marking
them as such with the "nonnull" attribute. We don't use it much in Linux
yet, but I do see a few places.

e.g.:

static inline bool __attribute__((nonnull(1,2)))
strends(const char *str, const char *suffix)

> +{
> +	unsigned int str_len = strlen(str), suffix_len = strlen(suffix);
> +
> +	if (str_len < suffix_len)
> +		return false;
> +
> +	return !(strcmp(str + str_len - suffix_len, suffix));
> +}

We should probably add it to strlen and strcmp as well. :)

> +
>  #endif /* _LINUX_STRING_H_ */
> diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
> index 0ed7448a26d3aa0fe9e2a6a894d4c49c2c0b86e0..f9a8e557ba7734c9848d58ff986407d8000f52ee 100644
> --- a/lib/tests/string_kunit.c
> +++ b/lib/tests/string_kunit.c
> @@ -602,6 +602,18 @@ static void string_test_memtostr(struct kunit *test)
>  	KUNIT_EXPECT_EQ(test, dest[7], '\0');
>  }
>  
> +static void string_test_strends(struct kunit *test)
> +{
> +	KUNIT_EXPECT_TRUE(test, strends("foo-bar", "bar"));
> +	KUNIT_EXPECT_TRUE(test, strends("foo-bar", "-bar"));
> +	KUNIT_EXPECT_TRUE(test, strends("foobar", "foobar"));
> +	KUNIT_EXPECT_TRUE(test, strends("foobar", ""));
> +	KUNIT_EXPECT_FALSE(test, strends("bar", "foobar"));
> +	KUNIT_EXPECT_FALSE(test, strends("", "foo"));
> +	KUNIT_EXPECT_FALSE(test, strends("foobar", "ba"));
> +	KUNIT_EXPECT_TRUE(test, strends("", ""));
> +}

Thanks for adding tests! :)

> +
>  static struct kunit_case string_test_cases[] = {
>  	KUNIT_CASE(string_test_memset16),
>  	KUNIT_CASE(string_test_memset32),
> @@ -623,6 +635,7 @@ static struct kunit_case string_test_cases[] = {
>  	KUNIT_CASE(string_test_strlcat),
>  	KUNIT_CASE(string_test_strtomem),
>  	KUNIT_CASE(string_test_memtostr),
> +	KUNIT_CASE(string_test_strends),
>  	{}
>  };
>  
> 
> -- 
> 2.51.0
> 

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook