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
setup_firstcall(FuncCallContext *funcctx, HStore *hs,
				FunctionCallInfoData *fcinfo)
{
	MemoryContext oldcontext;
	HStore	   *st;

	oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

	st = (HStore *) palloc(VARSIZE(hs));
	memcpy(st, hs, VARSIZE(hs));

	funcctx->user_fctx = (void *) st;

	if (fcinfo)
	{
		TupleDesc	tupdesc;

		/* Build a tuple descriptor for our result type */
		if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
			elog(ERROR, "return type must be a row type");

		funcctx->tuple_desc = BlessTupleDesc(tupdesc);
	}

	MemoryContextSwitchTo(oldcontext);
}

setup_firstcall(FuncCallContext *funcctx, HStore *hs,
				FunctionCallInfoData *fcinfo)
{
	MemoryContext oldcontext;
	HStore	   *st;

	oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

	st = (HStore *) palloc(VARSIZE(hs));
	memcpy(st, hs, VARSIZE(hs));

	funcctx->user_fctx = (void *) st;

	if (fcinfo)
	{
		TupleDesc	tupdesc;

		/* Build a tuple descriptor for our result type */
		if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
			elog(ERROR, "return type must be a row type");

		funcctx->tuple_desc = BlessTupleDesc(tupdesc);
	}

	MemoryContextSwitchTo(oldcontext);
}
