[PATCH v2 1/5] lib: string: Fix strlcpy return value

[Sean Anderson <seanga2@gmail.com>]

On 3/11/21 12:15 AM, Sean Anderson wrote:
> strlcpy should always return the number of bytes copied. We were
> accidentally missing the nul-terminator. We also always used to return a

It looks like I was a bit bullish in assuming a mistake. After reviewing
the man page, it looks like the nul-terminator is intentionally
excluded.

> The strlcpy() and strlcat() functions return the total length of the
> string they tried to create. For strlcpy() that means the length of
> src. For strlcat() that means the initial length of dst plus the
> length of src. While this may seem somewhat confusing, it was done to
> make truncation detection simple.

In particular, we should return the length of the string, which may be
different from the amount of bytes copied. However, the non-zero return
value should be fixed.

> non-zero value, even if we did not actually copy anything.
> 
> Fixes: 23cd138503 ("Integrate USB gadget layer and USB CDC driver layer")
> 
> Signed-off-by: Sean Anderson <seanga2@gmail.com>
> ---
> 
> Changes in v2:
> - New
> 
>   lib/string.c | 12 ++++++++----
>   1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/string.c b/lib/string.c
> index 73b984123d..1b867ac09d 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -114,17 +114,21 @@ char * strncpy(char * dest,const char *src,size_t count)
>    * NUL-terminated string that fits in the buffer (unless,
>    * of course, the buffer size is zero). It does not pad
>    * out the result like strncpy() does.
> + *
> + * Return: the number of bytes copied
>    */
>   size_t strlcpy(char *dest, const char *src, size_t size)
>   {
> -	size_t ret = strlen(src);
> -
>   	if (size) {
> -		size_t len = (ret >= size) ? size - 1 : ret;
> +		size_t srclen = strlen(src);
> +		size_t len = (srclen >= size) ? size - 1 : srclen;
> +
>   		memcpy(dest, src, len);
>   		dest[len] = '\0';
> +		return len + 1;
>   	}
> -	return ret;
> +
> +	return 0;
>   }
>   #endif
>   
>