[PATCH bpf-next v3 1/2] bpf: add bpf_strcasecmp kfunc

[PATCH bpf-next v3 1/2] bpf: add bpf_strcasecmp kfunc

[Rong Tao]

From: Rong Tao <rongtao@cestc.cn>

bpf_strcasecmp() function performs same like bpf_strcmp() except ignoring
the case of the characters.

Signed-off-by: Rong Tao <rongtao@cestc.cn>
---
 kernel/bpf/helpers.c | 68 +++++++++++++++++++++++++++++++-------------
 1 file changed, 48 insertions(+), 20 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 401b4932cc49..238fd992c786 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3349,45 +3349,72 @@ __bpf_kfunc void __bpf_trap(void)
  * __get_kernel_nofault instead of plain dereference to make them safe.
  */
 
-/**
- * bpf_strcmp - Compare two strings
- * @s1__ign: One string
- * @s2__ign: Another string
- *
- * Return:
- * * %0       - Strings are equal
- * * %-1      - @s1__ign is smaller
- * * %1       - @s2__ign is smaller
- * * %-EFAULT - Cannot read one of the strings
- * * %-E2BIG  - One of strings is too large
- * * %-ERANGE - One of strings is outside of kernel address space
- */
-__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
+int __bpf_strcasecmp(const char *s1, const char *s2, bool ignore_case)
 {
 	char c1, c2;
 	int i;
 
-	if (!copy_from_kernel_nofault_allowed(s1__ign, 1) ||
-	    !copy_from_kernel_nofault_allowed(s2__ign, 1)) {
+	if (!copy_from_kernel_nofault_allowed(s1, 1) ||
+	    !copy_from_kernel_nofault_allowed(s2, 1)) {
 		return -ERANGE;
 	}
 
 	guard(pagefault)();
 	for (i = 0; i < XATTR_SIZE_MAX; i++) {
-		__get_kernel_nofault(&c1, s1__ign, char, err_out);
-		__get_kernel_nofault(&c2, s2__ign, char, err_out);
+		__get_kernel_nofault(&c1, s1, char, err_out);
+		__get_kernel_nofault(&c2, s2, char, err_out);
+		if (ignore_case) {
+			c1 = tolower(c1);
+			c2 = tolower(c2);
+		}
 		if (c1 != c2)
 			return c1 < c2 ? -1 : 1;
 		if (c1 == '\0')
 			return 0;
-		s1__ign++;
-		s2__ign++;
+		s1++;
+		s2++;
 	}
 	return -E2BIG;
 err_out:
 	return -EFAULT;
 }
 
+/**
+ * bpf_strcmp - Compare two strings
+ * @s1__ign: One string
+ * @s2__ign: Another string
+ *
+ * Return:
+ * * %0       - Strings are equal
+ * * %-1      - @s1__ign is smaller
+ * * %1       - @s2__ign is smaller
+ * * %-EFAULT - Cannot read one of the strings
+ * * %-E2BIG  - One of strings is too large
+ * * %-ERANGE - One of strings is outside of kernel address space
+ */
+__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
+{
+	return __bpf_strcasecmp(s1__ign, s2__ign, false);
+}
+
+/**
+ * bpf_strcasecmp - Compare two strings, ignoring the case of the characters
+ * @s1__ign: One string
+ * @s2__ign: Another string
+ *
+ * Return:
+ * * %0       - Strings are equal
+ * * %-1      - @s1__ign is smaller
+ * * %1       - @s2__ign is smaller
+ * * %-EFAULT - Cannot read one of the strings
+ * * %-E2BIG  - One of strings is too large
+ * * %-ERANGE - One of strings is outside of kernel address space
+ */
+__bpf_kfunc int bpf_strcasecmp(const char *s1__ign, const char *s2__ign)
+{
+	return __bpf_strcasecmp(s1__ign, s2__ign, true);
+}
+
 /**
  * bpf_strnchr - Find a character in a length limited string
  * @s__ign: The string to be searched
@@ -3832,6 +3859,7 @@ BTF_ID_FLAGS(func, bpf_iter_dmabuf_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
 #endif
 BTF_ID_FLAGS(func, __bpf_trap)
 BTF_ID_FLAGS(func, bpf_strcmp);
+BTF_ID_FLAGS(func, bpf_strcasecmp);
 BTF_ID_FLAGS(func, bpf_strchr);
 BTF_ID_FLAGS(func, bpf_strchrnul);
 BTF_ID_FLAGS(func, bpf_strnchr);
-- 
2.51.0

Re: [PATCH bpf-next v3 1/2] bpf: add bpf_strcasecmp kfunc

[Viktor Malik]

On 9/2/25 11:19, Rong Tao wrote:
> From: Rong Tao <rongtao@cestc.cn>
> 
> bpf_strcasecmp() function performs same like bpf_strcmp() except ignoring
> the case of the characters.
> 
> Signed-off-by: Rong Tao <rongtao@cestc.cn>

For the series:

Acked-by: Viktor Malik <vmalik@redhat.com>

> ---
>  kernel/bpf/helpers.c | 68 +++++++++++++++++++++++++++++++-------------
>  1 file changed, 48 insertions(+), 20 deletions(-)
> 
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 401b4932cc49..238fd992c786 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -3349,45 +3349,72 @@ __bpf_kfunc void __bpf_trap(void)
>   * __get_kernel_nofault instead of plain dereference to make them safe.
>   */
>  
> -/**
> - * bpf_strcmp - Compare two strings
> - * @s1__ign: One string
> - * @s2__ign: Another string
> - *
> - * Return:
> - * * %0       - Strings are equal
> - * * %-1      - @s1__ign is smaller
> - * * %1       - @s2__ign is smaller
> - * * %-EFAULT - Cannot read one of the strings
> - * * %-E2BIG  - One of strings is too large
> - * * %-ERANGE - One of strings is outside of kernel address space
> - */
> -__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
> +int __bpf_strcasecmp(const char *s1, const char *s2, bool ignore_case)
>  {
>  	char c1, c2;
>  	int i;
>  
> -	if (!copy_from_kernel_nofault_allowed(s1__ign, 1) ||
> -	    !copy_from_kernel_nofault_allowed(s2__ign, 1)) {
> +	if (!copy_from_kernel_nofault_allowed(s1, 1) ||
> +	    !copy_from_kernel_nofault_allowed(s2, 1)) {
>  		return -ERANGE;
>  	}
>  
>  	guard(pagefault)();
>  	for (i = 0; i < XATTR_SIZE_MAX; i++) {
> -		__get_kernel_nofault(&c1, s1__ign, char, err_out);
> -		__get_kernel_nofault(&c2, s2__ign, char, err_out);
> +		__get_kernel_nofault(&c1, s1, char, err_out);
> +		__get_kernel_nofault(&c2, s2, char, err_out);
> +		if (ignore_case) {
> +			c1 = tolower(c1);
> +			c2 = tolower(c2);
> +		}
>  		if (c1 != c2)
>  			return c1 < c2 ? -1 : 1;
>  		if (c1 == '\0')
>  			return 0;
> -		s1__ign++;
> -		s2__ign++;
> +		s1++;
> +		s2++;
>  	}
>  	return -E2BIG;
>  err_out:
>  	return -EFAULT;
>  }
>  
> +/**
> + * bpf_strcmp - Compare two strings
> + * @s1__ign: One string
> + * @s2__ign: Another string
> + *
> + * Return:
> + * * %0       - Strings are equal
> + * * %-1      - @s1__ign is smaller
> + * * %1       - @s2__ign is smaller
> + * * %-EFAULT - Cannot read one of the strings
> + * * %-E2BIG  - One of strings is too large
> + * * %-ERANGE - One of strings is outside of kernel address space
> + */
> +__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
> +{
> +	return __bpf_strcasecmp(s1__ign, s2__ign, false);
> +}
> +
> +/**
> + * bpf_strcasecmp - Compare two strings, ignoring the case of the characters
> + * @s1__ign: One string
> + * @s2__ign: Another string
> + *
> + * Return:
> + * * %0       - Strings are equal
> + * * %-1      - @s1__ign is smaller
> + * * %1       - @s2__ign is smaller
> + * * %-EFAULT - Cannot read one of the strings
> + * * %-E2BIG  - One of strings is too large
> + * * %-ERANGE - One of strings is outside of kernel address space
> + */
> +__bpf_kfunc int bpf_strcasecmp(const char *s1__ign, const char *s2__ign)
> +{
> +	return __bpf_strcasecmp(s1__ign, s2__ign, true);
> +}
> +
>  /**
>   * bpf_strnchr - Find a character in a length limited string
>   * @s__ign: The string to be searched
> @@ -3832,6 +3859,7 @@ BTF_ID_FLAGS(func, bpf_iter_dmabuf_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
>  #endif
>  BTF_ID_FLAGS(func, __bpf_trap)
>  BTF_ID_FLAGS(func, bpf_strcmp);
> +BTF_ID_FLAGS(func, bpf_strcasecmp);
>  BTF_ID_FLAGS(func, bpf_strchr);
>  BTF_ID_FLAGS(func, bpf_strchrnul);
>  BTF_ID_FLAGS(func, bpf_strnchr);

Re: [PATCH bpf-next v3 1/2] bpf: add bpf_strcasecmp kfunc

[Yonghong Song]

On 9/2/25 2:19 AM, Rong Tao wrote:
> From: Rong Tao <rongtao@cestc.cn>
>
> bpf_strcasecmp() function performs same like bpf_strcmp() except ignoring
> the case of the characters.
>
> Signed-off-by: Rong Tao <rongtao@cestc.cn>
> ---
>   kernel/bpf/helpers.c | 68 +++++++++++++++++++++++++++++++-------------
>   1 file changed, 48 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 401b4932cc49..238fd992c786 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -3349,45 +3349,72 @@ __bpf_kfunc void __bpf_trap(void)
>    * __get_kernel_nofault instead of plain dereference to make them safe.
>    */
>   
> -/**
> - * bpf_strcmp - Compare two strings
> - * @s1__ign: One string
> - * @s2__ign: Another string
> - *
> - * Return:
> - * * %0       - Strings are equal
> - * * %-1      - @s1__ign is smaller
> - * * %1       - @s2__ign is smaller
> - * * %-EFAULT - Cannot read one of the strings
> - * * %-E2BIG  - One of strings is too large
> - * * %-ERANGE - One of strings is outside of kernel address space
> - */
> -__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
> +int __bpf_strcasecmp(const char *s1, const char *s2, bool ignore_case)

The function __bpf_strcasecmp should be a static function.

>   {
>   	char c1, c2;
>   	int i;
>   
> -	if (!copy_from_kernel_nofault_allowed(s1__ign, 1) ||
> -	    !copy_from_kernel_nofault_allowed(s2__ign, 1)) {
> +	if (!copy_from_kernel_nofault_allowed(s1, 1) ||
> +	    !copy_from_kernel_nofault_allowed(s2, 1)) {
>   		return -ERANGE;
>   	}
>   
>   	guard(pagefault)();
>   	for (i = 0; i < XATTR_SIZE_MAX; i++) {
> -		__get_kernel_nofault(&c1, s1__ign, char, err_out);
> -		__get_kernel_nofault(&c2, s2__ign, char, err_out);
> +		__get_kernel_nofault(&c1, s1, char, err_out);
> +		__get_kernel_nofault(&c2, s2, char, err_out);
> +		if (ignore_case) {
> +			c1 = tolower(c1);
> +			c2 = tolower(c2);
> +		}
>   		if (c1 != c2)
>   			return c1 < c2 ? -1 : 1;
>   		if (c1 == '\0')
>   			return 0;
> -		s1__ign++;
> -		s2__ign++;
> +		s1++;
> +		s2++;
>   	}
>   	return -E2BIG;
>   err_out:
>   	return -EFAULT;
>   }
>   
> +/**
> + * bpf_strcmp - Compare two strings
> + * @s1__ign: One string
> + * @s2__ign: Another string
> + *
> + * Return:
> + * * %0       - Strings are equal
> + * * %-1      - @s1__ign is smaller
> + * * %1       - @s2__ign is smaller
> + * * %-EFAULT - Cannot read one of the strings
> + * * %-E2BIG  - One of strings is too large
> + * * %-ERANGE - One of strings is outside of kernel address space
> + */
> +__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
> +{
> +	return __bpf_strcasecmp(s1__ign, s2__ign, false);
> +}
> +
> +/**
> + * bpf_strcasecmp - Compare two strings, ignoring the case of the characters
> + * @s1__ign: One string
> + * @s2__ign: Another string
> + *
> + * Return:
> + * * %0       - Strings are equal
> + * * %-1      - @s1__ign is smaller
> + * * %1       - @s2__ign is smaller
> + * * %-EFAULT - Cannot read one of the strings
> + * * %-E2BIG  - One of strings is too large
> + * * %-ERANGE - One of strings is outside of kernel address space
> + */
> +__bpf_kfunc int bpf_strcasecmp(const char *s1__ign, const char *s2__ign)
> +{
> +	return __bpf_strcasecmp(s1__ign, s2__ign, true);
> +}
> +
>   /**
>    * bpf_strnchr - Find a character in a length limited string
>    * @s__ign: The string to be searched
> @@ -3832,6 +3859,7 @@ BTF_ID_FLAGS(func, bpf_iter_dmabuf_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
>   #endif
>   BTF_ID_FLAGS(func, __bpf_trap)
>   BTF_ID_FLAGS(func, bpf_strcmp);
> +BTF_ID_FLAGS(func, bpf_strcasecmp);
>   BTF_ID_FLAGS(func, bpf_strchr);
>   BTF_ID_FLAGS(func, bpf_strchrnul);
>   BTF_ID_FLAGS(func, bpf_strnchr);

Re: [PATCH bpf-next v3 1/2] bpf: add bpf_strcasecmp kfunc

[Rong Tao]

On 9/3/25 00:54, Yonghong Song wrote:
>
>
> On 9/2/25 2:19 AM, Rong Tao wrote:
>> From: Rong Tao <rongtao@cestc.cn>
>>
>> bpf_strcasecmp() function performs same like bpf_strcmp() except 
>> ignoring
>> the case of the characters.
>>
>> Signed-off-by: Rong Tao <rongtao@cestc.cn>
>> ---
>>   kernel/bpf/helpers.c | 68 +++++++++++++++++++++++++++++++-------------
>>   1 file changed, 48 insertions(+), 20 deletions(-)
>>
>> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
>> index 401b4932cc49..238fd992c786 100644
>> --- a/kernel/bpf/helpers.c
>> +++ b/kernel/bpf/helpers.c
>> @@ -3349,45 +3349,72 @@ __bpf_kfunc void __bpf_trap(void)
>>    * __get_kernel_nofault instead of plain dereference to make them 
>> safe.
>>    */
>>   -/**
>> - * bpf_strcmp - Compare two strings
>> - * @s1__ign: One string
>> - * @s2__ign: Another string
>> - *
>> - * Return:
>> - * * %0       - Strings are equal
>> - * * %-1      - @s1__ign is smaller
>> - * * %1       - @s2__ign is smaller
>> - * * %-EFAULT - Cannot read one of the strings
>> - * * %-E2BIG  - One of strings is too large
>> - * * %-ERANGE - One of strings is outside of kernel address space
>> - */
>> -__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
>> +int __bpf_strcasecmp(const char *s1, const char *s2, bool ignore_case)
>
> The function __bpf_strcasecmp should be a static function.

Thanks a lot, I just add 'static' and tested it, submit V4, please review.

Rong Tao

>
>>   {
>>       char c1, c2;
>>       int i;
>>   -    if (!copy_from_kernel_nofault_allowed(s1__ign, 1) ||
>> -        !copy_from_kernel_nofault_allowed(s2__ign, 1)) {
>> +    if (!copy_from_kernel_nofault_allowed(s1, 1) ||
>> +        !copy_from_kernel_nofault_allowed(s2, 1)) {
>>           return -ERANGE;
>>       }
>>         guard(pagefault)();
>>       for (i = 0; i < XATTR_SIZE_MAX; i++) {
>> -        __get_kernel_nofault(&c1, s1__ign, char, err_out);
>> -        __get_kernel_nofault(&c2, s2__ign, char, err_out);
>> +        __get_kernel_nofault(&c1, s1, char, err_out);
>> +        __get_kernel_nofault(&c2, s2, char, err_out);
>> +        if (ignore_case) {
>> +            c1 = tolower(c1);
>> +            c2 = tolower(c2);
>> +        }
>>           if (c1 != c2)
>>               return c1 < c2 ? -1 : 1;
>>           if (c1 == '\0')
>>               return 0;
>> -        s1__ign++;
>> -        s2__ign++;
>> +        s1++;
>> +        s2++;
>>       }
>>       return -E2BIG;
>>   err_out:
>>       return -EFAULT;
>>   }
>>   +/**
>> + * bpf_strcmp - Compare two strings
>> + * @s1__ign: One string
>> + * @s2__ign: Another string
>> + *
>> + * Return:
>> + * * %0       - Strings are equal
>> + * * %-1      - @s1__ign is smaller
>> + * * %1       - @s2__ign is smaller
>> + * * %-EFAULT - Cannot read one of the strings
>> + * * %-E2BIG  - One of strings is too large
>> + * * %-ERANGE - One of strings is outside of kernel address space
>> + */
>> +__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
>> +{
>> +    return __bpf_strcasecmp(s1__ign, s2__ign, false);
>> +}
>> +
>> +/**
>> + * bpf_strcasecmp - Compare two strings, ignoring the case of the 
>> characters
>> + * @s1__ign: One string
>> + * @s2__ign: Another string
>> + *
>> + * Return:
>> + * * %0       - Strings are equal
>> + * * %-1      - @s1__ign is smaller
>> + * * %1       - @s2__ign is smaller
>> + * * %-EFAULT - Cannot read one of the strings
>> + * * %-E2BIG  - One of strings is too large
>> + * * %-ERANGE - One of strings is outside of kernel address space
>> + */
>> +__bpf_kfunc int bpf_strcasecmp(const char *s1__ign, const char 
>> *s2__ign)
>> +{
>> +    return __bpf_strcasecmp(s1__ign, s2__ign, true);
>> +}
>> +
>>   /**
>>    * bpf_strnchr - Find a character in a length limited string
>>    * @s__ign: The string to be searched
>> @@ -3832,6 +3859,7 @@ BTF_ID_FLAGS(func, bpf_iter_dmabuf_destroy, 
>> KF_ITER_DESTROY | KF_SLEEPABLE)
>>   #endif
>>   BTF_ID_FLAGS(func, __bpf_trap)
>>   BTF_ID_FLAGS(func, bpf_strcmp);
>> +BTF_ID_FLAGS(func, bpf_strcasecmp);
>>   BTF_ID_FLAGS(func, bpf_strchr);
>>   BTF_ID_FLAGS(func, bpf_strchrnul);
>>   BTF_ID_FLAGS(func, bpf_strnchr);
>

re: [PATCH bpf-next v3 1/2] bpf: add bpf_strcasecmp kfunc

[Sebastian Ramadan]

Hi,

While reviewing the recent patch ([PATCH bpf-next v3 1/2] bpf: add
bpf_strcasecmp kfunc), I noticed a small but important standards
compliance issue regarding the use of tolower() with char variables:

char c1, c2;
// ...
if (ignore_case) {
    c1 = tolower(c1);
    c2 = tolower(c2);
}

According to the ISO C standard, functions and macros in <ctype.h>
(such as tolower()) are only defined for arguments that are either:
1/ Representable as an unsigned char, or
2/ Equal to the special value EOF.

Passing a plain char that contains a negative value (other than EOF)
results in undefined behavior. This can easily go unnoticed in
environments where char defaults to unsigned (such as GCC on x86), but
will break or behave unpredictably on platforms where char is signed.

To ensure portable and defined behavior, it's typically recommended to
cast to unsigned char before passing to tolower():

c1 = tolower((unsigned char)c1);
c2 = tolower((unsigned char)c2);

This ensures compliance with the standard and avoids silent issues
across different toolchains and architectures.

While this may not cause immediate problems in the GNU-C ecosystem,
implicitly relying on compiler-specific behavior can gradually reduce
the kernel's portability. Keeping these cases in check helps maintain
the kernel's long-standing goal of wide platform support.

Thanks for your time, and for the ongoing work toward clean and
portable kernel code.

Regards, Sebastian Ramadan