Program runs out of memory after resolving many domains under a security manager?

Question

I have a service where domain names to be resolved come from untrusted sources. Recently, it kept crashing from running out of memory. I narrowed down the possible reasons, and came to the conclusion that it must be related to the recent flux of DNS requests. However, the service doesn't store anything after resolving domain names, so this seemed unlikely, but I tried spamming my service with requests that result in it resolving domain names, just in case. It did die from that. I then narrowed down the code to this after concluding that there is no memory being stored on my code's behalf: ``` import java.math.*; import java.net.*; class A { static { try { for (BigInteger i = BigInteger.ZERO; i==i; i = i.add(BigInteger.ONE)) Inet4Address.getByName("a"+i+".dog"); } catch (Exception e) {throw new RuntimeException(e);} } } ``` I setup dnsmasq with this line in `/etc/dnsmasq.conf` to make the resolutions faster: ``` address=/dog/127.0.0.1 ``` At first when I ran this, it survived for days,…

Accepted Answer

" InetAddress class has a cache to store successful as well as unsuccessful host name resolutions. By default, when a security manager is installed, in order to protect against DNS spoofing attacks, the result of positive host name resolutions are cached forever. When a security manager is not installed, the default behavior is to cache entries for a finite (implementation dependent) period of time. The result of unsuccessful host name resolution is cached for a very short period of time (10 seconds) to improve performance."

source: javadoc for InetAddress.java http://docs.oracle.com/javase/6/docs/api/java/net/InetAddress.html

I think it is caching all the hostnames resolved forever and causing outOfMemoryError finally.

You can try setting Java security properties control the TTL( time to live) and see if this helps in solving this problem

Program runs out of memory after resolving many domains under a security manager?

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