Re: [xml] xmlUTF8Strpos()'s use of xmlUTF8Strlen()

["William M. Brack" <wbrack mmm com hk>]

Bill Moseley said:
> I'm wondering why xmlUTF8Strpos() needs to call xmlUTF8Strlen().
>
>     const xmlChar *
>     xmlUTF8Strpos(const xmlChar *utf, int pos) {
>         xmlChar ch;
>
>         if (utf == NULL) return(NULL);
>         if ( (pos < 0) || (pos >= xmlUTF8Strlen(utf)) )
>             return(NULL);
>         while (pos--) {
>             if ((ch=*utf++) == 0) return(NULL);
>
> xmlUTF8Strpos() is already checking for a \0 byte so doesn't seem like it
> does any good to go over the string twice: once in xmlUTF8Strlen() and then
> again in xmlUTF8Strpos().

The problem which this is meant to guard against is a caller passing in a
large value for pos which potentially causes a crash (analogous to the check
for a NULL pointer).  Since the 'while' loop is starting from the end of the
string and working backward, the check within the loop for termination doesn't
help.

> And the problem I'm having is I'm *not* passing in a \0 terminated utf-8
> string, so xmlUTF8Strlen() can end up running off the end of the
> buffer looking for the end of the string.
>
> The reason I'm not passing in a \0 terminated string is that I'm using
> UTF8Toisolat1() to convert the utf-8 string passed to my SAX character
> handler (which is not null-terminated), and then calling
> xmlUTF8Strpos() to skip over any chars that could not be converted to
> 8859-1.
>
> --
> Bill Moseley
> moseley hank org

I understand your point, but I'm reluctant to change the routine (for the
reason given above).  I also understand that xmlUTF8Strlen doesn't completely
guard against the problem (but I think it helps).  Further input / discussion
from the list would be welcome.

Bill