Predict integer overflow to avoid buffer overruns.

Several functions, mostly type input functions, calculated an allocation
size such that the calculation wrapped to a small positive value when
arguments implied a sufficiently-large requirement.  Writes past the end
of the inadvertent small allocation followed shortly thereafter.
Coverity identified the path_in() vulnerability; code inspection led to
the rest.  In passing, add check_stack_depth() to prevent stack overflow
in related functions.

Back-patch to 8.4 (all supported versions).  The non-comment hstore
changes touch code that did not exist in 8.4, so that part stops at 9.0.

Noah Misch and Heikki Linnakangas, reviewed by Tom Lane.

Security: CVE-2014-0064
bitxor(PG_FUNCTION_ARGS)
{
	VarBit	   *arg1 = PG_GETARG_VARBIT_P(0);
	VarBit	   *arg2 = PG_GETARG_VARBIT_P(1);
	VarBit	   *result;
	int			len,
				bitlen1,
				bitlen2,
				i;
	bits8	   *p1,
			   *p2,
			   *r;
	bits8		mask;

	bitlen1 = VARBITLEN(arg1);
	bitlen2 = VARBITLEN(arg2);
	if (bitlen1 != bitlen2)
		ereport(ERROR,
				(errcode(ERRCODE_STRING_DATA_LENGTH_MISMATCH),
				 errmsg("cannot XOR bit strings of different sizes")));

	len = VARSIZE(arg1);
	result = (VarBit *) palloc(len);
	SET_VARSIZE(result, len);
	VARBITLEN(result) = bitlen1;

	p1 = VARBITS(arg1);
	p2 = VARBITS(arg2);
	r = VARBITS(result);
	for (i = 0; i < VARBITBYTES(arg1); i++)
		*r++ = *p1++ ^ *p2++;

	/* Pad the result */
	mask = BITMASK << VARBITPAD(result);
	if (mask)
	{
		r--;
		*r &= mask;
	}

	PG_RETURN_VARBIT_P(result);
}

bitxor(PG_FUNCTION_ARGS)
{
	VarBit	   *arg1 = PG_GETARG_VARBIT_P(0);
	VarBit	   *arg2 = PG_GETARG_VARBIT_P(1);
	VarBit	   *result;
	int			len,
				bitlen1,
				bitlen2,
				i;
	bits8	   *p1,
			   *p2,
			   *r;
	bits8		mask;

	bitlen1 = VARBITLEN(arg1);
	bitlen2 = VARBITLEN(arg2);
	if (bitlen1 != bitlen2)
		ereport(ERROR,
				(errcode(ERRCODE_STRING_DATA_LENGTH_MISMATCH),
				 errmsg("cannot XOR bit strings of different sizes")));

	len = VARSIZE(arg1);
	result = (VarBit *) palloc(len);
	SET_VARSIZE(result, len);
	VARBITLEN(result) = bitlen1;

	p1 = VARBITS(arg1);
	p2 = VARBITS(arg2);
	r = VARBITS(result);
	for (i = 0; i < VARBITBYTES(arg1); i++)
		*r++ = *p1++ ^ *p2++;

	/* Pad the result */
	mask = BITMASK << VARBITPAD(result);
	if (mask)
	{
		r--;
		*r &= mask;
	}

	PG_RETURN_VARBIT_P(result);
}
