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[PATCH v4 01/10] string: provide strends()

Bartosz Golaszewski posted 10 patches 1 month ago
[PATCH v4 01/10] string: provide strends()
Posted by Bartosz Golaszewski 1 month ago 
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.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.
+ */
+static inline bool 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));
+}
+
 #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("", ""));
+}
+
 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
Re: [PATCH v4 01/10] string: provide strends()
Posted by Kees Cook 4 weeks, 1 day ago 
On Wed, Nov 12, 2025 at 02:55:30PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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@linaro.org>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.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@kernel.org>

-- 
Kees Cook
Re: [PATCH v4 01/10] string: provide strends()
Posted by Bartosz Golaszewski 4 weeks, 1 day ago 
On Mon, Nov 17, 2025 at 9:33 PM Kees Cook <kees@kernel.org> wrote:
>
> On Wed, Nov 12, 2025 at 02:55:30PM +0100, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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@linaro.org>
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> > ---

Hi Kees!

Thanks for the review. I already queued this for v6.19, so let me
address the issues in a follow-up.

> >  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"?
>

But they do, please see the test.

> > + */
> > +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)
>

Ok.

> > +{
> > +     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. :)
>

Sure but that's outside of the scope of this.

Bart
Re: [PATCH v4 01/10] string: provide strends()
Posted by Andy Shevchenko 4 weeks, 1 day ago 
On Tue, Nov 18, 2025 at 11:47 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> On Mon, Nov 17, 2025 at 9:33 PM Kees Cook <kees@kernel.org> wrote:
> > On Wed, Nov 12, 2025 at 02:55:30PM +0100, Bartosz Golaszewski wrote:

...

> > > + * True if @str ends with @suffix. False in all other cases.
> >
> > Maybe added "empty strings never match"?
>
> But they do, please see the test.

I also think that "" == "" (on the same page as Bart). Why should we
make it different?

-- 
With Best Regards,
Andy Shevchenko

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