mkhtemp: harden tmpdir access control

faccessat used this way respects uid/gid,
handles ACLs (where used), and matches whatt
many real security tools might do.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/libreboot-utils/lib/mkhtemp.c

@@ -475,6 +475,12 @@ world_writeable_and_sticky(
 		goto sticky_hell; /* not sticky */
 	}
 
+	/* if anyone even looks at you funny, drop
+	 * everything on the floor and refuse to function
+	 */
+	if (faccessat(dirfd, 	".", X_OK, AT_EACCESS) < 0)
+		goto sticky_hell;
+
 	/* non-world-writeable, so
 	 * stickiness is do-not-care
 	 */