Re: [PATCH 2.6]: IPv6: strcpy -> strlcpy

On Fri, 2003-11-28 at 01:40, YOSHIFUJI Hideaki / 吉藤英明 wrote:

In article [ref] (at Fri, 28 Nov 2003 09:26:42 +0900 (JST)), YOSHIFUJI Hideaki / 吉藤英明 [off-list ref] says:

quoted

quoted

 3)   if (len)
         strncpy(dst, src, len - 1);
      dst[len] = 0;

grr, another mistake...:

          if (len) {
             strncpy(dst, src, len - 1);
             dst[len - 1];
          }

----------------
1) use strlcpy0(dst, src, len)

size_t strlcpy0(char *dst, const char *src, size_t maxlen)
{
  size_t len = strlcpy(dst, src, maxlen);
  if (likely(maxlen != 0) && len < maxlen - 1)
    memset(dst + len + 1, 0, maxlen - len - 1);
}

2a) use strncpy0(dst, src, len)

char *strncpy0(char *dst, const char *src, size_t maxlen)
{
  memset(dst, 0, maxlen);
  if (likely(maxlen != 0))
    strncpy(dst, src, maxlen - 1);
}

2b) fix strncpy() to zero-out rest of destination buffer 
    and use strncpy0(dst, src, len)

char *strncpy0(char *dst, const char *src, size_t maxlen)
{
  if (likely(maxlen != 0)) {
    strncpy(dst, src, maxlen - 1);
    dst[maxlen - 1] = 0;
  }
}


I prefer 1 > 2b >> 2a.

What about coding a new function str0cpy()?

/**
 * str0cpy - Copy a length-limited, %NUL-terminated string
 * @dest: Where to copy the string to
 * @src: Where to copy the string from
 * @count: The maximum number of bytes to copy
 */
char * str0cpy(char * dest,const char *src,size_t count)
{
        if (count) {
                char *tmp = dest;

                count--;
                while (count) {
                        if ((*tmp = *src) != 0) src++;
                        tmp++;
                        count--;
                }
                *tmp = 0;
        }
        return dest;
}

It behaves like strncpy() but correctly null-terminates the string in
every case.