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Showing posts from April, 2014

C++ After a Long Time

We were facing a weird issue on our almost stable dns infrastructure. We use PDNS servers and our custom backend to serve DNS requests. So the PDNS server pipes the request to custom backend, the backend reads from the pipe and puts the result back in the pipe which is served back to the client by the server. This intro is not at all useful to the post. So please ignore it.
The problem started since Monday where randomly our PDNS backend started using 100% CPU and the PDNS server started crashing. The backend was written in C++ and the debugging started. The backend had no debug mode to start with (!). So we attached all backend processes to strace. Strace showed a particularly crafted DNS request put the backend in infinite loop. We couldn't get the whole request in the strace as it was bigger than default 32 bytes. We started strace with -s 5000 to capture 5000 bytes. Now the dns request is found. The domain name is 312 bytes long. A full domain should not exceed 253 characters…