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SubjectRe: [PATCH v5 1/3] lib/ucs2_string: Add UCS-2 strscpy function
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On 8/4/23 10:18, Kees Cook wrote:
> On Sun, Jul 30, 2023 at 06:19:02PM +0200, Maximilian Luz wrote:
>> Add a ucs2_strscpy() function for UCS-2 strings. The behavior is
>> equivalent to the standard strscpy() function, just for 16-bit character
>> UCS-2 strings.
>>
>> Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
>> ---
>>
>> Changes in v5:
>> - Add ucs2_strscpy() instead of ucs2_strlcpy()
>>
>> Patch introduced in v4.
>>
>> ---
>> include/linux/ucs2_string.h | 1 +
>> lib/ucs2_string.c | 35 +++++++++++++++++++++++++++++++++++
>> 2 files changed, 36 insertions(+)
>>
>> diff --git a/include/linux/ucs2_string.h b/include/linux/ucs2_string.h
>> index cf3ada3e820e..c499ae809c7d 100644
>> --- a/include/linux/ucs2_string.h
>> +++ b/include/linux/ucs2_string.h
>> @@ -10,6 +10,7 @@ typedef u16 ucs2_char_t;
>> unsigned long ucs2_strnlen(const ucs2_char_t *s, size_t maxlength);
>> unsigned long ucs2_strlen(const ucs2_char_t *s);
>> unsigned long ucs2_strsize(const ucs2_char_t *data, unsigned long maxlength);
>> +ssize_t ucs2_strscpy(ucs2_char_t *dst, const ucs2_char_t *src, size_t count);
>> int ucs2_strncmp(const ucs2_char_t *a, const ucs2_char_t *b, size_t len);
>>
>> unsigned long ucs2_utf8size(const ucs2_char_t *src);
>> diff --git a/lib/ucs2_string.c b/lib/ucs2_string.c
>> index 0a559a42359b..b608129fcbdc 100644
>> --- a/lib/ucs2_string.c
>> +++ b/lib/ucs2_string.c
>> @@ -32,6 +32,41 @@ ucs2_strsize(const ucs2_char_t *data, unsigned long maxlength)
>> }
>> EXPORT_SYMBOL(ucs2_strsize);
>>
>> +ssize_t ucs2_strscpy(ucs2_char_t *dst, const ucs2_char_t *src, size_t count)
>> +{
>> + long res;
>> +
>> + /*
>> + * Ensure that we have a valid amount of space. We need to store at
>> + * least one NUL-character.
>> + */
>> + if (count == 0 || WARN_ON_ONCE(count > INT_MAX))
>
> Is "count" a measure of bytes or characters? It seems to be characters.
> can you please add some kern-doc for this function to clarify this.
> Also, I wonder if the above check should be "count > INT_MAX / 2" since
> the INT_MAX is, generally, done in byte counts.

Count is a measure of characters. I'll add a doc-comment.

Regarding INT_MAX / 2: I'm fine with either. I'd change it to
INT_MAX / sizeof(*dst) if you say it's generally enforced in bytes.

>> + return -E2BIG;
>> +
>> + /*
>> + * Copy at most 'count' bytes, return early if we find a
>
> If "count" is characters, this comment should not say "bytes". :)

Correct. Will fix this.

>> + * NUL-terminator.
>> + */
>> + for (res = 0; res < count; res++) {
>> + ucs2_char_t c;
>> +
>> + c = src[res];
>> + dst[res] = c;
>> +
>> + if (!c)
>> + return res;
>> + }
>> +
>> + /*
>> + * The loop above terminated without finding a NUL-terminator,
>> + * exceeding the 'count': Enforce proper NUL-termination and return
>> + * error.
>> + */
>> + dst[count - 1] = 0;
>> + return -E2BIG;
>> +}
>> +EXPORT_SYMBOL(ucs2_strscpy);
>> +
>> int
>> ucs2_strncmp(const ucs2_char_t *a, const ucs2_char_t *b, size_t len)
>> {
>> --
>> 2.41.0
>>
>
> Otherwise looks good to me!

Thanks!

Regards
Max

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