Remove clever code

[alejandro-colomar]

shadow/src/groupmod.c

Line 619 in 37412f5

(void) snprintf (info_group.action+strlen (info_group.action),

If I I'm not missing something, this is a buffer overrun in the snprintf(3) call. I have plans to address it, which include defining this function for use in the entire project:

char *
shdw_stpeprintf(char *str, char *past_end, const char *restrict fmt, ...)
{
	int      len;
	char     *p;
	va_list  ap;

	if (str == past_end)
		return past_end;

	if (str == NULL)
		return NULL;

	va_start(ap, fmt);
	len = vsnprintf(str, past_end - str, fmt, ap);
	va_end(ap);

	if (len == -1)
		return NULL;

	if (len >= past_end - str)
		return past_end;

	return str + len;
}

This is a wrapper for snprintf(3) which allows easy chaining, and detecting truncation. Its design is very similar to stpecpy(3), which I designed here: https://software.codidact.com/posts/285946/287522#answer-287522

[alejandro-colomar]

Ahh, there's no overrun; there was a clever subtraction. Anyway, I still want to remove the cleverness, to avoid confusions and accidents.

[alejandro-colomar]

Fixed by #636