alt Hacker NewsIt's a upstream targeted fix that was made available significantly faster in packages/images maintained by volunteers, it's not some untested downstream patch. Customers at this point would have likely taken their applications offline over this issue so it would have been difficult to make the situation any worse.
Given the sheer number of PHP applications out there, it's impossible to conclude with certainty that this targeted fix will have no regressive impact without significant testing. How much testing needs to be done is debatable, but I'm pretty sure the answer isn't zero.