Force program to use /dev/urandom

Question

I'm trying to create a little container that will let me remap /dev/random to /dev/urandom without root for a specific program. What I have so far:

unshare -r bash -c 'chroot . /bin/busybox sh'

For the most part, this seems to act as a full chroot, equivalent to sudo chroot . /bin/busybox sh, but one problem: When I try to mknod somefile c 1 9, I get operation not permitted. This works in a standard chroot. Is it possible to get around this? If not, is there a better way to do what I am attempting?

Please don't drown me in comments about the security of random vs urandom. That's not what this is about.

Answer 1

If the program is dynamically linked, you can override the file opening function by preloading a library. See Redirect a file descriptor before execution for some sample code; replace /dev/null by /dev/urandom and set PATH_TO_OVERRIDE=/dev/random in the build command.