AGWA / ldpreload

Some useful LD_PRELOAD libraries

Andrew's LD_PRELOAD libraries

To compile, run make.

ldpreload-forcerdonly.so

Convert read/write open calls to read-only. Useful for programs that open a file read/write but never write to it.

ldpreload-forceurandom.so

Convert open calls of /dev/random to /dev/urandom, because /dev/urandom on Linux is secure while (on old kernels) /dev/random is stupidly slow.

ldpreload-prebind.so

Intercepts bind calls for particular TCP or UDP port numbers and replaces them with a dup3 call from a file descriptor of your choosing. This is useful for making an off-the-shelf server program listen on a pre-bound file descriptor that you pass to it. For example, a privileged supervisor process could bind to a privileged port like 443, drop privileges, and then launch the server process with the pre-bound socket on file descriptor 3. Although some server programs support listening on a pre-bound file descriptor, most do not, requiring the use of ldpreload-prebind.so.

The following environment variables are used to configure ldpreload-prebind.so (replace 443 with the port number and 3 with the prebound file descriptor number):

• TCPFD_443=3 for a TCP port
• UDPFD_443=3 for a UDP port

ldpreload-unixbind.so

Intercepts bind calls for particular TCP/IP port numbers, and replaces them with a bind to a UNIX domain socket of your choosing. When a connection is accepted on the socket, the local and remote IP addresses are read from the connection using the the PROXY protocol v2, and made available via getpeername, getsockname, and the addr argument to accept.

The following environment variable is used to configure ldpreload-unixbind.so (replace 443 with the port number and /path/to/socket with the path to the UNIX domain socket):

• SOCKET_PATH_443=/path/to/socket