Can I restrict access to certain files for a certain process?

Question

Is it possible to start a process in Linux, and restrict its access to certain files/directories? For example:

$ start-process --enable-dir=./sandbox --exec="some-script.sh"

some-script.sh won't be able to do anything outside of ./sandbox.

Answer 1

You can use chroot to set the root directory of your process tree. This means however, that all dependencies of that process must be available in it's new root.

There are a number of packages that can help you setup chroot-environments for your needs. Google is your friend ;)

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Some pointers on building a chroot environment

When builing a chroot for some program or daemon you have to have a complete environment for the program you want to chroot. This means you have to provide a minimum system in a directory. That might contain:

• A shell and some shell utilities, or a variant of busybox. (this encompasses the next step too, if you aren't planning on deploying one single static executable that is).
• Libc and other dependent shared libraries.
  • You need to check shared library dependencies using ldd or objdump. Every library that appears has to be in your private root directory. This step might be repeated several times for every executable and library you need. Note that some libraries, which are linked explicitly at runtime using dlopen need to be checked separately.
• Depending on what you plan to chroot a minimal /dev tree.
  • If you plan to chroot a daemon process this may well be needing some minimal files in /dev such as random or zero. You can create those with the mknod command. Please refer to the mknod documentation, as well as the linux documentation on which major/minor numbers which device should have.
• Also depending on what you plan to chroot is a minimal /etc. Files needed therein are:
  • A minimal passwd and shadow (not your system passwd/shadow).
  • A minimal mtab containing /.
  • A minimal group (again, not your system group file).

You have to start somewhere, so it's best to start with the prerequisites for you program. Refer to your documentation for specifics.

Answer 2

Typically you want to chroot the process, so that it can only access a directory and its sub-directories, and only execute some defined commands.

See How to chroot.