This is a tool for playing with Linux 5.13's new Landlock feature.

Landlock lets processes lock themselves into a subset of their file access permissions.

It's a fork of the samples/landlock/sandboxer.c tool by Mickaël Salaün, which ships with the kernel source, changing environment variable parsing to flag parsing, and making it easier to compile standalone and play with the feature. It's not meant as a serious sandboxing tool.

Example:

root(302)@virtual:~# ./lljail -r /usr -r /bin -rw /tmp -r /etc -r /root -- /bin/bash
root(681)@virtual:~# echo lol > cat  # fails (read-only directory)
bash: cat: Permission denied
root(681)@virtual:~# cd /tmp
root(681)@virtual:/tmp# echo lol > cat  # succeeds (read-write directory)
root(681)@virtual:/tmp#

Remark: Landlock's support will keep the proces from opening files for reading and writing, but some syscalls can currently not be restricted yet, such as stat().

You can see this for example when using the file utility: It will still detect that the file is there, using stat(), but it only recognizes its content once it has the read permissions.

root(207)@virtual:~# ./lljail -r /usr -r file /etc/magic -- /bin/file text.txt
text.txt: writable, regular file, no read permission
root(207)@virtual:~# ./lljail -r /usr -r file /etc/magic -r file text.txt -- /bin/file text.txt
text.txt: ASCII text