Is this serious? Does this mean if I have an app, Java, PHP or whatever, which eventually calls glibc's gethostbyname gethostbyaddr, my machine is owned? That somebody could just craft a special hostname or ip address to lookup? So all those websites where you enter hostname o IP address to lookup something like whois info or ping other machines, could be owned?
If it affects gethostbyaddr that'd be really bad - there are a lot of applications that automatically look up reverse DNS on a connection.
Mail servers in particular generally make it pretty easy to trigger both forward and reverse lookups.
The test case seems to have it looking up an ip address as if it were a name, but it's using the reentrant version of the function - maybe only those are affected?
