Description:
------------
When a double value stored within the session file, the web server might crash. It was a mystical problem for us. To solve this issue, there need some workaround at the VAR_UNSERIALIZER.RE source code:

"d:" (iv | nv | nvexp) ";"	{
	*p = YYCURSOR;
	INIT_PZVAL(*rval);
	ZVAL_DOUBLE(*rval, atof(start + 2));
	return 1;
}

The problem is the difference in the implementation of the function 'atof'. While general C implementations looks ahead until a non digital character found, microsoft C tries to determine the string's length with a call to 'strlen'. This can couse the crash some times, when the accessible memory doesn't contain '\0'. The report about the memory dump is following in the 'Reproducible code' section. For a quick sight I placed the various implementations of the 'atof' function within the 'Expected result' block.

As we figured out, this issue comes up only when unserializing sessions, not zval represented strings, as those zvals are closed with '\0'.


Reproduce code:
---------------
Here is the report from Microsoft. They thought somthings wrong with PHP... :)

Call stack:
----------------
0c19e228 019240e2 1b0419d8 43e72508 03019af0 msvcrt!atof+0x25 (CONV: cdecl)
[atof.c @ 57]
WARNING: Stack unwind information not available. Following frames may be
wrong.
0c19e2d4 03019b88 1b097000 0c19e3b4 43e72508 php4ts+0x940e2
03019c88 00000000 00010002 00000000 0005006d 0x3019b88

00 0c19e1f8 780167f9 msvcrt!strlen(void)+0x20 [intel\strlen.asm @ 78]
01 0c19e228 019240e2 msvcrt!atof(char * nptr = 0x1b0419d8
"1077611306196.2860107421875;a:5:{s:5:"tabid";s:5:"tab_5";s:3:"ct0";s:13:"1077612213758";s:3:"ct1";a:1:{s:13:"403b0afeae402";s:13:"1077612210164";}}s:9:"post_vars";a:0:...


Expected result:
----------------
-- MICROSOFT C IMPLEMENTATION --

double __cdecl atof(
        REG1 const char *nptr
        )
{

#ifdef _MT
        struct _flt fltstruct;      /* temporary structure */
#endif  /* _MT */

        /* scan past leading space/tab characters */

        while ( isspace((int)(unsigned char)*nptr) )
                nptr++;

        /* let _fltin routine do the rest of the work */

#ifdef _MT
        return( *(double *)&(_fltin2( &fltstruct, nptr, strlen(nptr), 0, 0 )->
        dval) );
#else  /* _MT */
        return( *(double *)&(_fltin( nptr, strlen(nptr), 0, 0 )->dval) );
#endif  /* _MT */
}

-- GENERAL C IMPLEMENTATION (may differ at some point) --

double
atof(p)
register char *p;
{
	register c;
	double fl, flexp, exp5;
	double big = 72057594037927936.;  /*2^56*/
	double ldexp();
	int nd;
	register eexp, exp, neg, negexp, bexp;

	neg = 1;
	while((c = *p++) == ' ')
		;
	if (c == '-')
		neg = -1;
	else if (c=='+')
		;
	else
		--p;

	exp = 0;
	fl = 0;
	nd = 0;
	while ((c = *p++), isdigit(c)) {
		if (fl<big)
			fl = 10*fl + (c-'0');
		else
			exp++;
		nd++;
	}

	if (c == '.') {
		while ((c = *p++), isdigit(c)) {
			if (fl<big) {
				fl = 10*fl + (c-'0');
				exp--;
			}
		nd++;
		}
	}

	negexp = 1;
	eexp = 0;
	if ((c == 'E') || (c == 'e')) {
		if ((c= *p++) == '+')
			;
		else if (c=='-')
			negexp = -1;
		else
			--p;

		while ((c = *p++), isdigit(c)) {
			eexp = 10*eexp+(c-'0');
		}
		if (negexp<0)
			eexp = -eexp;
		exp = exp + eexp;
	}

	negexp = 1;
	if (exp<0) {
		negexp = -1;
		exp = -exp;
	}


	if((nd+exp*negexp) < -LOGHUGE){
		fl = 0;
		exp = 0;
	}
	flexp = 1;
	exp5 = 5;
	bexp = exp;
	for (;;) {
		if (exp&01)
			flexp *= exp5;
		exp >>= 1;
		if (exp==0)
			break;
		exp5 *= exp5;
	}
	if (negexp<0)
		fl /= flexp;
	else
		fl *= flexp;
	fl = ldexp(fl, negexp*bexp);
	if (neg<0)
		fl = -fl;
	return(fl);
}