It attaches the LSM BPF program when the system manager starts up.
It populates the hash of maps BPF map when services that have
RestrictFileSystems= set start.
It cleans up the hash of maps when the unit cgroup is pruned.
To pass the file descriptor of the BPF map we add it to the keep_fds
array.
This adds 6 functions to implement RestrictFileSystems=
* lsm_bpf_supported() checks if LSM BPF is supported. It checks that
cgroupv2 is used, that BPF LSM is enabled, and tries to load the BPF
LSM program which makes sure BTF and hash of maps are supported, and
BPF LSM programs can be loaded.
* lsm_bpf_setup() loads and attaches the LSM BPF program.
* lsm_bpf_unit_restrict_filesystems() populates the hash of maps BPF map with the
cgroupID and the set of allowed or denied filesystems.
* lsm_bpf_cleanup() removes a cgroupID entry from the hash of maps.
* lsm_bpf_map_restrict_fs_fd() is a helper function to get the file
descriptor of the BPF map.
* lsm_bpf_destroy() is a wrapper around the destroy function of the BPF
skeleton file.
It hooks into the file_open LSM hook and allows only when the filesystem
where the open will take place is present in a BPF map for a particular
cgroup.
The BPF map used is a hash of maps with the following structure:
cgroupID -> (s_magic -> uint32)
The inner map is effectively a set.
The entry at key 0 in the inner map encodes whether the program behaves
as an allow list or a deny list: if its value is 0 it is a deny list,
otherwise it is an allow list.
When the cgroupID is present in the map, the program checks the inner
map for the magic number of the filesystem associated with the file
that's being opened. When the program behaves as an allow list, if that
magic number is present it allows the open to succeed, when the program
behaves as a deny list, it only allows access if the that magic number
is NOT present. When access is denied the program returns -EPERM.
The BPF program uses CO-RE (Compile-Once Run-Everywhere) to access
internal kernel structures without needing kernel headers present at
runtime.
Only accept DT_REG/DT_LNK/DT_DIR entries, ignore all others.
Only accpet DT_REG/DT_LNK for file names that are valid unit file names.
Only accept DT_DIR for filenames that are valid unit file names which
are suffixed by .d, .wants, .requires
This doesn't really fix any bugs, but tightens what we insert into the
lookup tables.
This verifies that the argv part of any exec_command parameters that
are sent through dbus is not empty at deserialization time.
There is an additional check in service.c service_verify() that again
checks if all exec_commands are correctly populated, after the service
has been loaded, whether through dbus or otherwise.
Fixes#20933.
These functions are used pretty much independently of locale, i.e. the
only info relevant is whether th locale is UTF-8 or not. Hence let's
give this its own pair of .c/.h files.
Let's make our service managers slightly less likely to be killed by the
OOM killer by adjusting our services' OOM score adjustment to 100 above
ours. Do this conservatively, i.e. only for regular user sessions.
Yu Watanabe
Iago López Galeiras
Lennart Poettering
Andrew Soutar
Henri Chain
Luca Boccassi
Egor
Zbigniew Jędrzejewski-Szmek