allowing /proc/self without allowing all of /proc (like the default base profile does) can still block /proc/self in child processes

[symphorien]

The default base config allows reading /proc/self:
https://github.com/landlock-lsm/island/blob/main/assets/landlock/island-default-base.toml#L46

however this is not fully effective: (illustrated with the zsh integration)

$ LANG=C bash -c "head -n1 /proc/self/status; head -n1 /proc/self/status"
head: cannot open '/proc/self/status' for reading: Permission denied
Name:	head

my understanding is that:

• the bash process, with PID X, has landlock ruleset allowing /proc/self as a symlink to /proc/X
• first head command is executed with fork(), so has a different pid, so /proc/self points to a directory /proc/Y which is not allowed
• second head command is executed with exec without fork, so proceeds to read /proc/X/status successfully

this is particularly annoying to debug.

Note that this is reproducible with landrun because it looks like a fundamental issue with landlock:

landrun --rw /home --rox /nix --rw /tmp --ro /etc/ --ro /proc/self --ro /run/current-system bash -c "/run/current-system/sw/bin/head /proc/self/status; /run/current-system/sw/bin/head /proc/self/status;"
head: cannot open '/proc/self/status' for reading: Permission denied
Name:	/run/current-sy
Umask:	0022
State:	R (running)
Tgid:	395443
Ngid:	0
Pid:	395443
PPid:	391428
TracerPid:	0
Uid:	1000	1000	1000	1000
Gid:	100	100	100	100

Maybe if island wants to hide other processes a pid namespace is more suitable? Or the whole of /proc should be allowed by default?