Code: poly_path(PG_FUNCTION_ARGS)
{
	POLYGON    *poly = PG_GETARG_POLYGON_P(0);
	PATH	   *path;
 	int			size;
 	int			i;
 
 	size = offsetof(PATH, p[0]) +sizeof(path->p[0]) * poly->npts;
 	path = (PATH *) palloc(size);
 
	SET_VARSIZE(path, size);
	path->npts = poly->npts;
	path->closed = TRUE;
	/* prevent instability in unused pad bytes */
	path->dummy = 0;

	for (i = 0; i < poly->npts; i++)
	{
		path->p[i].x = poly->p[i].x;
		path->p[i].y = poly->p[i].y;
	}

	PG_RETURN_PATH_P(path);
}

Commit Message: 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
CWE ID: CWE-189
poly_path(PG_FUNCTION_ARGS)
{
	POLYGON    *poly = PG_GETARG_POLYGON_P(0);
	PATH	   *path;
 	int			size;
 	int			i;
 
	/*
	 * Never overflows: the old size fit in MaxAllocSize, and the new size is
	 * smaller by a small constant.
	 */
 	size = offsetof(PATH, p[0]) +sizeof(path->p[0]) * poly->npts;
 	path = (PATH *) palloc(size);
 
	SET_VARSIZE(path, size);
	path->npts = poly->npts;
	path->closed = TRUE;
	/* prevent instability in unused pad bytes */
	path->dummy = 0;

	for (i = 0; i < poly->npts; i++)
	{
		path->p[i].x = poly->p[i].x;
		path->p[i].y = poly->p[i].y;
	}

	PG_RETURN_PATH_P(path);
}
