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Introduction

Force programs to bind to different ports.

inet-remap is not meant for regular use. However, sometimes you're faced with a closed source binary that just has bind to some specific port. For whatever reason, you may want to have it bind to a different port. In such cases, inet-remap can help you bend that closed source binary to your will.

Use cases include forcing an application to bind to an unprivileged port and running the same application twice, each instance binding to different ports.

inet-remap uses LD_PRELOAD to intercept bind() calls. When a bind() call is intercepted, the protocol and port number used are looked up in a table parsed from the INET_REMAP environment variable. You can specify a remapping as protocol:old_port:new_port, where protocol can be either tcp or udp. You can specify multiple remappings by separating them with a comma or a space.

For example, to remap TCP port 7331 to 1337:

inet-remap -b tcp:7331:1337 ./program

Which behind the scenes is the same as:

LD_PRELOAD=libinet-remap-preload.so INET_REMAP=tcp:7331:1337 ./program

Or remap multiple ports:

inet-remap -b tcp:503:2503 -b udp:53:2053  ./program

Which comes down to:

LD_PRELOAD=libinet-remap-preload.so INET_REMAP=tcp:503:2503,udp:53:2053 ./program

Note that as a security precaution LD_PRELOAD and thus inet-remap do not work with setuid binaries or binaries with elevated privileges on most UNIX systems.

TODO:

  • Finish setting up build scripts.
  • Support IPv6.
  • Make protocol specification in remaps optional.
  • Support filtering based on IP address as well as protocol and port number.
  • Support for intercepting connect() calls to alter remote endpoints.
  • Get rid of non-POSIX SO_PROTOCOL socket option.
  • Add an executable/script wrapper for easy invocation.