Commit bec50680a31834619e66cb8b97edd6d5b5f15701
2012-02-15T20:12:32
Stop crashing in evdns when nameserver probes give a weird error When a nameserver is down, we periodically try sending a "probe" message to that nameserver to see if it has come back up. If a nameserver comes up, we cancel any pending probe messages. Cancelling a probe message while handling the probe's response would result in a access-after-free or a double-free, so when we notice that we're about to call a nameserver up because of having received a probe from it, we need to check whether current response is the response from the probe. There was a case where we didn't to that, though: when the resolver gave us an unusual error response to our request that it resolve google.com. This is pretty rare, but apparently it can happen with some weird cacheing nameservers -- the one on the mikrotik router, for example. Without this patch, we would crash with a NULL pointer derefernce. Thanks to Hannes Sowa for finding this issue and helping me track it down.