Bug in SVR2V2 stdio, sscanf() function, FIX

[Bruce Robertson]

Description:
	There is a serious bug in the System V Release 2 Version 2 sscanf()
	function.  This function does its work by creating a fake
	FILE structure with the _file field set to _NFILE, and the
	buffer base and count fields delimiting the string that sscanf()
	is supposed to scan.  This works great normally; the getc() macro
	pulls characters out of the string just fine.  When the end of
	the string is reached, getc() calls the _filbuf() function.  The
	_file field value of _NFILE is *supposed* to tell _filbuf()
	that this is a fake FILE structure, and just EOF should be
	returned.  Unfortunately, _filbuf() neglects this little detail,
	and tries to do all sorts of nasty things to the fake FILE
	structure.
	sscanf() stomps on this bug if there are more format descriptors
	in the format string than there are fields in the string that
	it is scanning.
	Come on guys, Berkeley got this right, though in a slightly
	different fashion!


Repeat-By:
	sscanf("a b c d", "%s %s %s %s %s", &a, &b, &c, &d, &e);

Fix:
*** /usr/src/lib/libc/port/stdio/filbuf.c-old	Tue Mar 25 21:23:23 1986
--- /usr/src/lib/libc/port/stdio/filbuf.c	Tue Mar 25 21:23:24 1986
***************
*** 14,19
  {
  	register FILE *diop;
  
  	if (iop->_base == NULL)  /* get buffer if we don't have one */
  		_findbuf(iop);
  

--- 14,22 -----
  {
  	register FILE *diop;
  
+ 	if ((iop->_flag & _IOEOF)  ||  iop->_file == _NFILE)
+ 		return EOF;
+ 
  	if (iop->_base == NULL)  /* get buffer if we don't have one */
  		_findbuf(iop);
  
-- 

	Bruce Robertson
	UUCP: cbosgd!utah-cs!utah-gr!stride!bruce
	ARPA: stride!bruce at utah-gr.arpa