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DNS Override

Used to override DNS settings for a single process (and its decendants) using the glibc resolv

See my post about it:
http://blog.backslasher.net/dns-override.html

How it works

The library monkeypatches fopen and looks for calls for /etc/resolv.conf, and returns a file pointer to a memory stream containing a customized version of resolv.conf.
The new resolv.conf is built by the script based on the current resolv.conf and passed as the RESOLV_CONF environment variable.
We then use LD_PRELOAD to insert our library (and version of fopen) before the "real" one.
It then execs the wanted binary.
Since both LD_PRELOAD and RESOLV_CONF are environment variables, they'll pass on to subprocesses too.

Common Usgae

  1. Build dns-override.so if needed (make dns-override.so)
  2. determine replacement DNS servers
  3. run desired file like so: ./dns-override.sh -s SERVER BINARY)
    Multiple servers can be specified, see script

Advanced usage

Run LD_PRELOAD=./dns-override.so:$LD_PRELOAD RESOLV_CONF=<new resolv conf contents> <binary>.
Do note that I'm only covering fopen which isn't used by all programs. For instance, python will be fooled but perl will not.

Testing

bats, perl and python are required.

  1. Run make test